From 2f7e1bbab3492528840ad372b948f9e599e7fb3f Mon Sep 17 00:00:00 2001
From: Alexei Anoshenko <anoshenko@gmail.com>
Date: Mon, 5 Sep 2022 14:00:07 +0300
Subject: [PATCH] Added SizeFunc interface, changed SizeUnit struct

---
 CHANGELOG.md               |   2 +
 README-ru.md               |  62 ++++++-
 README.md                  |  56 +++++-
 background.go              |   4 +-
 backgroundConicGradient.go |   4 +-
 backgroundGradient.go      |  31 ++--
 border.go                  |   9 +-
 bounds.go                  |  15 +-
 canvas.go                  |   6 +-
 checkbox.go                |   2 +-
 columnSeparator.go         |   5 +-
 gridLayout.go              |   6 +-
 listView.go                |  10 +-
 outline.go                 |   8 +-
 propertyGet.go             |   3 +
 propertySet.go             |   9 +-
 radius.go                  |  24 +--
 resizable.go               |   4 +-
 shadow.go                  |  14 +-
 sizeFunc.go                | 359 +++++++++++++++++++++++++++++++++++++
 sizeFunc_test.go           |  50 ++++++
 sizeUnit.go                |  72 +++++---
 tableView.go               |  16 +-
 view.go                    |  10 +-
 viewClip.go                |  22 +--
 viewStyle.go               |  10 +-
 viewTransform.go           |  24 +--
 27 files changed, 691 insertions(+), 146 deletions(-)
 create mode 100644 sizeFunc.go
 create mode 100644 sizeFunc_test.go

diff --git a/CHANGELOG.md b/CHANGELOG.md
index cccadc9..c87de36 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 * Requires go 1.18 or higher
 * The "interface{}" type replaced by "any"
+* Added SizeFunc interface and Function field to SizeUnit struct
+* Added MaxSize, MinSize, SumSize, SubSize, MulSize, DivSize, ClampSize functions
 * Added "list-row-gap", "list-column-gap", "accent-color", "tab-size", "overflow", 
 "arrow", "arrow-align", "arrow-size", "arrow-width", and "arrow-offset" properties 
 * Added "@ruiArrowSize" and "@ruiArrowWidth" constants to the default theme
diff --git a/README-ru.md b/README-ru.md
index 2f00c07..9058210 100644
--- a/README-ru.md
+++ b/README-ru.md
@@ -57,12 +57,12 @@
 SizeUnit объявлена как
 
 	type SizeUnit struct {
-		Type  SizeUnitType
-		Value float64
+		Type     SizeUnitType
+		Value    float64
+		Function SizeFunc
 	}
 
-где Type - тип размера;
-Value - размер
+где Type - тип размера; Value - размер; Function - функция (используется только если Type == SizeFunction, в остальных случаях игнорируется).
 
 Тип может принимать следующие значения:
 
@@ -79,12 +79,13 @@ Value - размер
 | 8        | SizeInMM       | поле Value определяет размер в миллиметрах.                                 |
 | 9        | SizeInCM       | поле Value определяет размер в сантиметрах.                                 |
 | 10       | SizeInFraction | поле Value определяет размер в частях. Используется только для задания размеров ячеек в GridLayout. |
+| 11       | SizeFunction   | поле Function задает функцию для вычисления размера. Значение поля Value игнорируется |
 
 Для более наглядного и простого задания переменных типа SizeUnit могут использоваться функции приведенные ниже
 
 | Функция        | Эквивалентное определение                          |
 |----------------|----------------------------------------------------|
-| rui.AutoSize() | rui.SizeUnit{ Type: rui.Auto, Value: 0 }           |
+| rui.AutoSize() | rui.SizeUnit{ Type: rui.Auto }                     |
 | rui.Px(n)      | rui.SizeUnit{ Type: rui.SizeInPixel, Value: n }    |
 | rui.Em(n)      | rui.SizeUnit{ Type: rui.SizeInEM, Value: n }       |
 | rui.Ex(n)      | rui.SizeUnit{ Type: rui.SizeInEX, Value: n }       |
@@ -96,7 +97,10 @@ Value - размер
 | rui.Cm(n)      | rui.SizeUnit{ Type: rui.SizeInCM, Value: n }       |
 | rui.Fr(n)      | rui.SizeUnit{ Type: rui.SizeInFraction, Value: n } |
 
-Переменные типа SizeUnit имеют текстовое представление (зачем оно нужно будет описано ниже). Текстовое представление состоит из числа (равному значению поля Value) и следующим за ним суффиксом определяющим тип. Исключением является значение типа Auto, которое имеет представление “auto”. Суффиксы перечислены в следующей таблице:
+Переменные типа SizeUnit имеют текстовое представление (зачем оно нужно будет описано ниже). 
+Текстовое представление состоит из числа (равному значению поля Value) и следующим за ним суффиксом определяющим тип. 
+Исключением является значение типа Auto, которое имеет представление “auto” и 
+значение типа SizeFunction, которое имеет особое представление. Суффиксы перечислены в следующей таблице:
 
 | Суффикс | Тип            |
 |:-------:|----------------|
@@ -119,6 +123,52 @@ Value - размер
 
 Получить текстовое представление структуры можно свойством String()
 
+#### SizeFunc
+
+Интерфейс SizeFunc используется для задания функции вычисляющей SizeUnit. Рассмотрим функции на примере функции min.
+
+Функция min находит минимальное значение среди заданных аргументов. Данная функция задается с помощью функции MinSize, объявленной как:
+
+	func MinSize(arg0, arg1 any, args ...any) SizeFunc
+
+Функция имеет 2 и более аргументов, каждый из которых может быть или SizeUnit или SizeFunc или string являющееся константой или
+текстовым представлением SizeUnit или SizeFunc.
+
+Примеры
+
+	rui.MizSize(rui.Percent(50), rui.Px(250))
+	rui.MizSize("50%", rui.Px(250), "40em")
+	rui.MizSize(rui.Percent(50), "@a1")
+
+Функция min имеет следующее текстовое представление
+
+	"min(<arg1>, <arg2>, ...)"
+
+где arg1, arg2, ... должны быть текстовым представлением SizeUnit или SizeFunc или константой. Например
+
+	"min(50%, 250px)"
+	"min(75%, @a1)"
+
+Интерфейс SizeFunc реализует интерфейс fmt.Stringer. 
+Функция String() этого интерфейса возвращает текстовое представление SizeFunc.
+
+Помимо min имеются следующие функции
+
+| Текстовое представление      | Функция для создания                 | Описание
+|------------------------------|--------------------------------------|-------------------------------------------------|
+| "min(<arg1>, <arg2>, ...)"   | MaxSize(arg0, arg1 any, args ...any) | находит минимальное значение среди аргументов   |
+| "sum(<arg1>, <arg2>, ...)"   | SumSize(arg0, arg1 any, args ...any) | находит сумму значений аргументов               |
+| "sub(<arg1>, <arg2>)"        | SubSize(arg0, arg1 any)              | находит разность значений аргументов            |
+| "mul(<arg1>, <arg2>)"        | MulSize(arg0, arg1 any)              | находит результат умножения значений аргументов |
+| "div(<arg1>, <arg2>)"        | DivSize(arg0, arg1 any)              | находит результат деления значений аргументов   |
+| "clamp(<min>, <val>, <max>)" | ClampSize(min, val, max any)         | ограничивает значение заданным диапазоном       |
+
+Дополнительные пояснения к функции "clamp(<min>, <val>, <max>)": результат вычисляется следующим образом:
+
+* if min ≤ val ≤ max then val;
+* if val < min then min;
+* if max < val then max;
+
 ### Color
 
 Тип Color описывает 32-битный цвет в формате ARGB:
diff --git a/README.md b/README.md
index 5fadc61..3803ee2 100644
--- a/README.md
+++ b/README.md
@@ -62,9 +62,10 @@ SizeUnit is declared as
 	type SizeUnit struct {
 		Type  SizeUnitType
 		Value float64
+		Function SizeFunc
 	}
 
-where Type is the type of size; Value is the size.
+where Type is the type of size; Value is the size; Function is function (used only if Type == SizeFunction, ignored otherwise)
 
 The Type can take the following values:
 
@@ -81,12 +82,13 @@ The Type can take the following values:
 | 8        | SizeInMM       | the Value field specifies the size in millimeters.                             |
 | 9        | SizeInCM       | the Value field defines the size in centimeters.                               |
 | 10       | SizeInFraction | the Value field specifies the size in parts. Used only for sizing cells of the GridLayout. |
+| 11       | SizeFunction   | the Function field specifies a function for calculating the size. The Value field is ignored |
 
 For a more visual and simple setting of variables of the SizeUnit type, the functions below can be used.
 
 | Function       | Equivalent definition                              |
 |----------------|----------------------------------------------------|
-| rui.AutoSize() | rui.SizeUnit{ Type: rui.Auto, Value: 0 }           |
+| rui.AutoSize() | rui.SizeUnit{ Type: rui.Auto }                     |
 | rui.Px(n)      | rui.SizeUnit{ Type: rui.SizeInPixel, Value: n }    |
 | rui.Em(n)      | rui.SizeUnit{ Type: rui.SizeInEM, Value: n }       |
 | rui.Ex(n)      | rui.SizeUnit{ Type: rui.SizeInEX, Value: n }       |
@@ -100,8 +102,8 @@ For a more visual and simple setting of variables of the SizeUnit type, the func
 
 Variables of the SizeUnit type have a textual representation (why you need it will be described below).
 The textual representation consists of a number (equal to the value of the Value field) followed by
-a suffix defining the type. An exception is a value of type Auto, which has the representation “auto”.
-The suffixes are listed in the following table:
+a suffix defining the type. 
+The exceptions are a value of type Auto, which has the representation "auto", and a value of type SizeFunction, which has a special representation. The suffixes are listed in the following table:
 
 | Suffix | Type           |
 |:------:|----------------|
@@ -124,6 +126,52 @@ To convert the textual representation to the SizeUnit structure, is used the fun
 
 You can get a textual representation of the structure using the String() function of SizeUnit structure
 
+#### SizeFunc
+
+The SizeFunc interface is used to define a function that calculates SizeUnit. Let's consider functions using the min function as an example.
+
+The min function finds the minimum value among the given arguments. This function is specified using the MinSize function, declared as:
+
+	func MinSize(arg0, arg1 any, args ...any) SizeFunc
+
+The function has 2 or more arguments, each of which can be either SizeUnit or SizeFunc or string which is a constant or
+text representation of SizeUnit or SizeFunc.
+
+Examples
+
+	rui.MizSize(rui.Percent(50), rui.Px(250))
+	rui.MizSize("50%", rui.Px(250), "40em")
+	rui.MizSize(rui.Percent(50), "@a1")
+
+The min function has the following text representation
+
+	"min(<arg1>, <arg2>, ...)"
+
+where arg1, arg2, ... must be a text representation of SizeUnit, or SizeFunc, or a constant. For example
+
+	"min(50%, 250px)"
+	"min(75%, @a1)"
+
+The SizeFunc interface implements the fmt.Stringer interface.
+The String() function of this interface returns the textual representation of SizeFunc.
+
+In addition to "min", there are the following functions
+
+| Text representation          | Function to create                   | Description                                              |
+|------------------------------|--------------------------------------|----------------------------------------------------------|
+| "min(<arg1>, <arg2>, ...)"   | MaxSize(arg0, arg1 any, args ...any) | finds the minimum value among the arguments              |
+| "sum(<arg1>, <arg2>, ...)"   | SumSize(arg0, arg1 any, args ...any) | calculates the sum of the argument values                |
+| "sub(<arg1>, <arg2>)"        | SubSize(arg0, arg1 any)              | calculates the subtraction of argument values            |
+| "mul(<arg1>, <arg2>)"        | MulSize(arg0, arg1 any)              | calculates the result of multiplying the argument values |
+| "div(<arg1>, <arg2>)"        | DivSize(arg0, arg1 any)              | calculates the result of dividing the argument values    |
+| "clamp(<min>, <val>, <max>)" | ClampSize(min, val, max any)         | limits value to specified range                          |
+
+Additional explanations for the function "clamp(<min>, <val>, <max>)": the result is calculated as follows:
+
+* if min ≤ val ≤ max then val;
+* if val < min then min;
+* if max < val then max;
+
 ### Color
 
 The Color type describes a 32-bit ARGB color:
diff --git a/background.go b/background.go
index f1ff1f9..692c73d 100644
--- a/background.go
+++ b/background.go
@@ -219,9 +219,9 @@ func (image *backgroundImage) cssStyle(session Session) string {
 
 			if width.Type != Auto || height.Type != Auto {
 				buffer.WriteString(` / `)
-				buffer.WriteString(width.cssString("auto"))
+				buffer.WriteString(width.cssString("auto", session))
 				buffer.WriteRune(' ')
-				buffer.WriteString(height.cssString("auto"))
+				buffer.WriteString(height.cssString("auto", session))
 			}
 		}
 
diff --git a/backgroundConicGradient.go b/backgroundConicGradient.go
index b52d30b..00ef8a1 100644
--- a/backgroundConicGradient.go
+++ b/backgroundConicGradient.go
@@ -316,9 +316,9 @@ func (gradient *backgroundConicGradient) cssStyle(session Session) string {
 			buffer.WriteRune(' ')
 		}
 		buffer.WriteString("at ")
-		buffer.WriteString(x.cssString("50%"))
+		buffer.WriteString(x.cssString("50%", session))
 		buffer.WriteString(" ")
-		buffer.WriteString(y.cssString("50%"))
+		buffer.WriteString(y.cssString("50%", session))
 		comma = true
 	}
 
diff --git a/backgroundGradient.go b/backgroundGradient.go
index d7b5eee..fcb0e61 100644
--- a/backgroundGradient.go
+++ b/backgroundGradient.go
@@ -261,19 +261,18 @@ func (gradient *backgroundGradient) writeGradient(session Session, buffer *strin
 				switch value := point.Pos.(type) {
 				case string:
 					if value != "" {
-						if value[0] == '@' {
-							value, _ = session.Constant(value[1:])
-						}
-						if pos, ok := StringToSizeUnit(value); ok && pos.Type != Auto {
-							buffer.WriteRune(' ')
-							buffer.WriteString(pos.cssString(""))
+						if value, ok := session.resolveConstants(value); ok {
+							if pos, ok := StringToSizeUnit(value); ok && pos.Type != Auto {
+								buffer.WriteRune(' ')
+								buffer.WriteString(pos.cssString("", session))
+							}
 						}
 					}
 
 				case SizeUnit:
 					if value.Type != Auto {
 						buffer.WriteRune(' ')
-						buffer.WriteString(value.cssString(""))
+						buffer.WriteString(value.cssString("", session))
 					}
 				}
 			}
@@ -512,9 +511,9 @@ func (gradient *backgroundRadialGradient) cssStyle(session Session) string {
 					if r, ok := StringToSizeUnit(text); ok && r.Type != Auto {
 						buffer.WriteString("ellipse ")
 						shapeText = ""
-						buffer.WriteString(r.cssString(""))
+						buffer.WriteString(r.cssString("", session))
 						buffer.WriteString(" ")
-						buffer.WriteString(r.cssString(""))
+						buffer.WriteString(r.cssString("", session))
 						buffer.WriteString(" ")
 					} else {
 						ErrorLog(`Invalid radial gradient radius: ` + text)
@@ -539,9 +538,9 @@ func (gradient *backgroundRadialGradient) cssStyle(session Session) string {
 			if value.Type != Auto {
 				buffer.WriteString("ellipse ")
 				shapeText = ""
-				buffer.WriteString(value.cssString(""))
+				buffer.WriteString(value.cssString("", session))
 				buffer.WriteString(" ")
-				buffer.WriteString(value.cssString(""))
+				buffer.WriteString(value.cssString("", session))
 				buffer.WriteString(" ")
 			}
 
@@ -553,7 +552,7 @@ func (gradient *backgroundRadialGradient) cssStyle(session Session) string {
 			buffer.WriteString("ellipse ")
 			shapeText = ""
 			for i := 0; i < count; i++ {
-				buffer.WriteString(value[i].cssString("50%"))
+				buffer.WriteString(value[i].cssString("50%", session))
 				buffer.WriteString(" ")
 			}
 
@@ -568,13 +567,13 @@ func (gradient *backgroundRadialGradient) cssStyle(session Session) string {
 				if value[i] != nil {
 					switch value := value[i].(type) {
 					case SizeUnit:
-						buffer.WriteString(value.cssString("50%"))
+						buffer.WriteString(value.cssString("50%", session))
 						buffer.WriteString(" ")
 
 					case string:
 						if text, ok := session.resolveConstants(value); ok {
 							if size, err := stringToSizeUnit(text); err == nil {
-								buffer.WriteString(size.cssString("50%"))
+								buffer.WriteString(size.cssString("50%", session))
 								buffer.WriteString(" ")
 							} else {
 								buffer.WriteString("50% ")
@@ -597,9 +596,9 @@ func (gradient *backgroundRadialGradient) cssStyle(session Session) string {
 			buffer.WriteString(shapeText)
 		}
 		buffer.WriteString("at ")
-		buffer.WriteString(x.cssString("50%"))
+		buffer.WriteString(x.cssString("50%", session))
 		buffer.WriteString(" ")
-		buffer.WriteString(y.cssString("50%"))
+		buffer.WriteString(y.cssString("50%", session))
 	}
 
 	buffer.WriteString(", ")
diff --git a/border.go b/border.go
index 29b317d..97a62f9 100644
--- a/border.go
+++ b/border.go
@@ -658,11 +658,14 @@ func (border *borderProperty) cssWidth(builder cssBuilder, session Session) {
 		borders.Top.Width == borders.Left.Width &&
 		borders.Top.Width == borders.Bottom.Width {
 		if borders.Top.Width.Type != Auto {
-			builder.add("border-width", borders.Top.Width.cssString("0"))
+			builder.add("border-width", borders.Top.Width.cssString("0", session))
 		}
 	} else {
-		builder.addValues("border-width", " ", borders.Top.Width.cssString("0"),
-			borders.Right.Width.cssString("0"), borders.Bottom.Width.cssString("0"), borders.Left.Width.cssString("0"))
+		builder.addValues("border-width", " ",
+			borders.Top.Width.cssString("0", session),
+			borders.Right.Width.cssString("0", session),
+			borders.Bottom.Width.cssString("0", session),
+			borders.Left.Width.cssString("0", session))
 	}
 }
 
diff --git a/bounds.go b/bounds.go
index 3a742bb..5de35bb 100644
--- a/bounds.go
+++ b/bounds.go
@@ -213,18 +213,21 @@ func (bounds *Bounds) String() string {
 		bounds.Bottom.String() + "," + bounds.Left.String()
 }
 
-func (bounds *Bounds) cssValue(tag string, builder cssBuilder) {
+func (bounds *Bounds) cssValue(tag string, builder cssBuilder, session Session) {
 	if bounds.allFieldsEqual() {
-		builder.add(tag, bounds.Top.cssString("0"))
+		builder.add(tag, bounds.Top.cssString("0", session))
 	} else {
-		builder.addValues(tag, " ", bounds.Top.cssString("0"), bounds.Right.cssString("0"),
-			bounds.Bottom.cssString("0"), bounds.Left.cssString("0"))
+		builder.addValues(tag, " ",
+			bounds.Top.cssString("0", session),
+			bounds.Right.cssString("0", session),
+			bounds.Bottom.cssString("0", session),
+			bounds.Left.cssString("0", session))
 	}
 }
 
-func (bounds *Bounds) cssString() string {
+func (bounds *Bounds) cssString(session Session) string {
 	var builder cssValueBuilder
-	bounds.cssValue("", &builder)
+	bounds.cssValue("", &builder, session)
 	return builder.finish()
 }
 
diff --git a/canvas.go b/canvas.go
index ff92252..d1c4df8 100644
--- a/canvas.go
+++ b/canvas.go
@@ -592,7 +592,7 @@ func (canvas *canvasData) writeFont(name string, script *strings.Builder) {
 
 func (canvas *canvasData) SetFont(name string, size SizeUnit) {
 	canvas.script.WriteString("\nctx.font = '")
-	canvas.script.WriteString(size.cssString("1em"))
+	canvas.script.WriteString(size.cssString("1rem", canvas.View().Session()))
 	canvas.writeFont(name, &canvas.script)
 }
 
@@ -616,7 +616,7 @@ func (canvas *canvasData) setFontWithParams(name string, size SizeUnit, params F
 		}
 	}
 
-	script.WriteString(size.cssString("1em"))
+	script.WriteString(size.cssString("1rem", canvas.View().Session()))
 	switch params.LineHeight.Type {
 	case Auto:
 
@@ -634,7 +634,7 @@ func (canvas *canvasData) setFontWithParams(name string, size SizeUnit, params F
 
 	default:
 		script.WriteString("/")
-		script.WriteString(params.LineHeight.cssString(""))
+		script.WriteString(params.LineHeight.cssString("", canvas.View().Session()))
 	}
 
 	canvas.writeFont(name, script)
diff --git a/checkbox.go b/checkbox.go
index b366066..83bd860 100644
--- a/checkbox.go
+++ b/checkbox.go
@@ -236,7 +236,7 @@ func (button *checkboxData) cssStyle(self View, builder cssBuilder) {
 	}
 
 	if gap, ok := sizeConstant(session, "ruiCheckboxGap"); ok && gap.Type != Auto && gap.Value > 0 {
-		builder.add("gap", gap.cssString("0"))
+		builder.add("gap", gap.cssString("0", session))
 	}
 
 	builder.add("align-items", "stretch")
diff --git a/columnSeparator.go b/columnSeparator.go
index 804269b..8e3a1d4 100644
--- a/columnSeparator.go
+++ b/columnSeparator.go
@@ -167,8 +167,9 @@ func (separator *columnSeparatorProperty) cssValue(session Session) string {
 	buffer := allocStringBuilder()
 	defer freeStringBuilder(buffer)
 
-	if value.Width.Type != Auto && value.Width.Type != SizeInFraction && value.Width.Value > 0 {
-		buffer.WriteString(value.Width.cssString(""))
+	if value.Width.Type != Auto && value.Width.Type != SizeInFraction &&
+		(value.Width.Value > 0 || value.Width.Type == SizeFunction) {
+		buffer.WriteString(value.Width.cssString("", session))
 	}
 
 	styles := enumProperties[BorderStyle].cssValues
diff --git a/gridLayout.go b/gridLayout.go
index 0db165f..384e72b 100644
--- a/gridLayout.go
+++ b/gridLayout.go
@@ -145,7 +145,7 @@ func (style *viewStyle) gridCellSizesCSS(tag string, session Session) string {
 
 	case 1:
 		if cellSize[0].Type != Auto {
-			return `repeat(auto-fill, ` + cellSize[0].cssString(`auto`) + `)`
+			return `repeat(auto-fill, ` + cellSize[0].cssString(`auto`, session) + `)`
 		}
 
 	default:
@@ -161,14 +161,14 @@ func (style *viewStyle) gridCellSizesCSS(tag string, session Session) string {
 		}
 		if !allAuto {
 			if allEqual {
-				return fmt.Sprintf(`repeat(%d, %s)`, len(cellSize), cellSize[0].cssString(`auto`))
+				return fmt.Sprintf(`repeat(%d, %s)`, len(cellSize), cellSize[0].cssString(`auto`, session))
 			}
 
 			buffer := allocStringBuilder()
 			defer freeStringBuilder(buffer)
 			for _, size := range cellSize {
 				buffer.WriteRune(' ')
-				buffer.WriteString(size.cssString(`auto`))
+				buffer.WriteString(size.cssString(`auto`, session))
 			}
 			return buffer.String()
 		}
diff --git a/listView.go b/listView.go
index d7ef071..e949c14 100644
--- a/listView.go
+++ b/listView.go
@@ -563,13 +563,13 @@ func (listView *listViewData) itemAlign(self View, buffer *strings.Builder) {
 func (listView *listViewData) itemSize(self View, buffer *strings.Builder) {
 	if itemWidth := GetListItemWidth(listView); itemWidth.Type != Auto {
 		buffer.WriteString(` min-width: `)
-		buffer.WriteString(itemWidth.cssString(""))
+		buffer.WriteString(itemWidth.cssString("", listView.Session()))
 		buffer.WriteRune(';')
 	}
 
 	if itemHeight := GetListItemHeight(listView); itemHeight.Type != Auto {
 		buffer.WriteString(` min-height: `)
-		buffer.WriteString(itemHeight.cssString(""))
+		buffer.WriteString(itemHeight.cssString("", listView.Session()))
 		buffer.WriteRune(';')
 	}
 }
@@ -659,7 +659,7 @@ func (listView *listViewData) checkboxItemDiv(self View, checkbox, hCheckboxAlig
 
 	if gap, ok := sizeConstant(listView.session, "ruiCheckboxGap"); ok && gap.Type != Auto {
 		itemStyleBuilder.WriteString(` grid-gap: `)
-		itemStyleBuilder.WriteString(gap.cssString("auto"))
+		itemStyleBuilder.WriteString(gap.cssString("auto", listView.Session()))
 		itemStyleBuilder.WriteRune(';')
 	}
 
@@ -896,13 +896,13 @@ func (listView *listViewData) htmlSubviews(self View, buffer *strings.Builder) {
 
 	if gap := GetListRowGap(listView); gap.Type != Auto {
 		buffer.WriteString(` row-gap: `)
-		buffer.WriteString(gap.cssString("0"))
+		buffer.WriteString(gap.cssString("0", listView.Session()))
 		buffer.WriteRune(';')
 	}
 
 	if gap := GetListColumnGap(listView); gap.Type != Auto {
 		buffer.WriteString(` column-gap: `)
-		buffer.WriteString(gap.cssString("0"))
+		buffer.WriteString(gap.cssString("0", listView.Session()))
 		buffer.WriteRune(';')
 	}
 
diff --git a/outline.go b/outline.go
index ea2ac95..342fa26 100644
--- a/outline.go
+++ b/outline.go
@@ -103,18 +103,18 @@ type ViewOutline struct {
 	Width SizeUnit
 }
 
-func (outline ViewOutline) cssValue(builder cssBuilder) {
+func (outline ViewOutline) cssValue(builder cssBuilder, session Session) {
 	values := enumProperties[BorderStyle].cssValues
 	if outline.Style > 0 && outline.Style < len(values) && outline.Color.Alpha() > 0 &&
 		outline.Width.Type != Auto && outline.Width.Type != SizeInFraction &&
 		outline.Width.Type != SizeInPercent && outline.Width.Value > 0 {
-		builder.addValues("outline", " ", outline.Width.cssString("0"), values[outline.Style], outline.Color.cssString())
+		builder.addValues("outline", " ", outline.Width.cssString("0", session), values[outline.Style], outline.Color.cssString())
 	}
 }
 
-func (outline ViewOutline) cssString() string {
+func (outline ViewOutline) cssString(session Session) string {
 	var builder cssValueBuilder
-	outline.cssValue(&builder)
+	outline.cssValue(&builder, session)
 	return builder.finish()
 }
 
diff --git a/propertyGet.go b/propertyGet.go
index e0ef75a..cc74a54 100644
--- a/propertyGet.go
+++ b/propertyGet.go
@@ -38,6 +38,9 @@ func valueToSizeUnit(value any, session Session) (SizeUnit, bool) {
 		case SizeUnit:
 			return value, true
 
+		case SizeFunc:
+			return SizeUnit{Type: SizeFunction, Function: value}, true
+
 		case string:
 			if text, ok := session.resolveConstants(value); ok {
 				return StringToSizeUnit(text)
diff --git a/propertySet.go b/propertySet.go
index e9ce7ee..34ead12 100644
--- a/propertySet.go
+++ b/propertySet.go
@@ -539,13 +539,20 @@ func (properties *propertyList) setSizeProperty(tag string, value any) bool {
 		switch value := value.(type) {
 		case string:
 			var ok bool
-			if size, ok = StringToSizeUnit(value); !ok {
+			if fn := parseSizeFunc(value); fn != nil {
+				size.Type = SizeFunction
+				size.Function = fn
+			} else if size, ok = StringToSizeUnit(value); !ok {
 				invalidPropertyValue(tag, value)
 				return false
 			}
 		case SizeUnit:
 			size = value
 
+		case SizeFunc:
+			size.Type = SizeFunction
+			size.Function = value
+
 		case float32:
 			size.Type = SizeInPixel
 			size.Value = float64(value)
diff --git a/radius.go b/radius.go
index 44cf6e9..fee7f1f 100644
--- a/radius.go
+++ b/radius.go
@@ -455,7 +455,7 @@ func (radius BoxRadius) String() string {
 	return buffer.String()
 }
 
-func (radius BoxRadius) cssValue(builder cssBuilder) {
+func (radius BoxRadius) cssValue(builder cssBuilder, session Session) {
 
 	if (radius.TopLeftX.Type == Auto || radius.TopLeftX.Value == 0) &&
 		(radius.TopLeftY.Type == Auto || radius.TopLeftY.Value == 0) &&
@@ -471,23 +471,23 @@ func (radius BoxRadius) cssValue(builder cssBuilder) {
 	buffer := allocStringBuilder()
 	defer freeStringBuilder(buffer)
 
-	buffer.WriteString(radius.TopLeftX.cssString("0"))
+	buffer.WriteString(radius.TopLeftX.cssString("0", session))
 
 	if radius.AllAnglesIsEqual() {
 
 		if !radius.TopLeftX.Equal(radius.TopLeftY) {
 			buffer.WriteString(" / ")
-			buffer.WriteString(radius.TopLeftY.cssString("0"))
+			buffer.WriteString(radius.TopLeftY.cssString("0", session))
 		}
 
 	} else {
 
 		buffer.WriteRune(' ')
-		buffer.WriteString(radius.TopRightX.cssString("0"))
+		buffer.WriteString(radius.TopRightX.cssString("0", session))
 		buffer.WriteRune(' ')
-		buffer.WriteString(radius.BottomRightX.cssString("0"))
+		buffer.WriteString(radius.BottomRightX.cssString("0", session))
 		buffer.WriteRune(' ')
-		buffer.WriteString(radius.BottomLeftX.cssString("0"))
+		buffer.WriteString(radius.BottomLeftX.cssString("0", session))
 
 		if !radius.TopLeftX.Equal(radius.TopLeftY) ||
 			!radius.TopRightX.Equal(radius.TopRightY) ||
@@ -495,22 +495,22 @@ func (radius BoxRadius) cssValue(builder cssBuilder) {
 			!radius.BottomRightX.Equal(radius.BottomRightY) {
 
 			buffer.WriteString(" / ")
-			buffer.WriteString(radius.TopLeftY.cssString("0"))
+			buffer.WriteString(radius.TopLeftY.cssString("0", session))
 			buffer.WriteRune(' ')
-			buffer.WriteString(radius.TopRightY.cssString("0"))
+			buffer.WriteString(radius.TopRightY.cssString("0", session))
 			buffer.WriteRune(' ')
-			buffer.WriteString(radius.BottomRightY.cssString("0"))
+			buffer.WriteString(radius.BottomRightY.cssString("0", session))
 			buffer.WriteRune(' ')
-			buffer.WriteString(radius.BottomLeftY.cssString("0"))
+			buffer.WriteString(radius.BottomLeftY.cssString("0", session))
 		}
 	}
 
 	builder.add("border-radius", buffer.String())
 }
 
-func (radius BoxRadius) cssString() string {
+func (radius BoxRadius) cssString(session Session) string {
 	var builder cssValueBuilder
-	radius.cssValue(&builder)
+	radius.cssValue(&builder, session)
 	return builder.finish()
 }
 
diff --git a/resizable.go b/resizable.go
index f6da563..4a65741 100644
--- a/resizable.go
+++ b/resizable.go
@@ -340,7 +340,7 @@ func (resizable *resizableData) updateResizeBorderWidth() {
 }
 
 func (resizable *resizableData) cellSizeCSS() (string, string) {
-	w := resizable.resizeBorderWidth().cssString("4px")
+	w := resizable.resizeBorderWidth().cssString("4px", resizable.Session())
 	side := resizable.getSide()
 	column := "1fr"
 	row := "1fr"
@@ -384,7 +384,7 @@ func (resizable *resizableData) htmlSubviews(self View, buffer *strings.Builder)
 	top := 1
 	leftSide := (side & LeftSide) != 0
 	rightSide := (side & RightSide) != 0
-	w := resizable.resizeBorderWidth().cssString("4px")
+	w := resizable.resizeBorderWidth().cssString("4px", resizable.Session())
 
 	if leftSide {
 		left = 2
diff --git a/shadow.go b/shadow.go
index 5d2825e..3d0541a 100644
--- a/shadow.go
+++ b/shadow.go
@@ -151,13 +151,13 @@ func (shadow *viewShadowData) cssStyle(buffer *strings.Builder, session Session,
 		buffer.WriteString("inset ")
 	}
 
-	buffer.WriteString(offsetX.cssString("0"))
+	buffer.WriteString(offsetX.cssString("0", session))
 	buffer.WriteByte(' ')
-	buffer.WriteString(offsetY.cssString("0"))
+	buffer.WriteString(offsetY.cssString("0", session))
 	buffer.WriteByte(' ')
-	buffer.WriteString(blurRadius.cssString("0"))
+	buffer.WriteString(blurRadius.cssString("0", session))
 	buffer.WriteByte(' ')
-	buffer.WriteString(spreadRadius.cssString("0"))
+	buffer.WriteString(spreadRadius.cssString("0", session))
 	buffer.WriteByte(' ')
 	buffer.WriteString(color.cssString())
 	return true
@@ -177,11 +177,11 @@ func (shadow *viewShadowData) cssTextStyle(buffer *strings.Builder, session Sess
 	}
 
 	buffer.WriteString(lead)
-	buffer.WriteString(offsetX.cssString("0"))
+	buffer.WriteString(offsetX.cssString("0", session))
 	buffer.WriteByte(' ')
-	buffer.WriteString(offsetY.cssString("0"))
+	buffer.WriteString(offsetY.cssString("0", session))
 	buffer.WriteByte(' ')
-	buffer.WriteString(blurRadius.cssString("0"))
+	buffer.WriteString(blurRadius.cssString("0", session))
 	buffer.WriteByte(' ')
 	buffer.WriteString(color.cssString())
 	return true
diff --git a/sizeFunc.go b/sizeFunc.go
new file mode 100644
index 0000000..cd76fd5
--- /dev/null
+++ b/sizeFunc.go
@@ -0,0 +1,359 @@
+package rui
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// SizeFunc describes a function that calculates the SizeUnit size.
+// Used as the value of the SizeUnit properties.
+// "min", "max", "clamp", "sum", "sub", "mul", and "div" functions are available.
+type SizeFunc interface {
+	fmt.Stringer
+	cssString(session Session) string
+	writeCSS(topFunc string, buffer *strings.Builder, session Session)
+	writeString(topFunc string, buffer *strings.Builder)
+}
+
+type sizeFuncData struct {
+	tag  string
+	args []any
+}
+
+func parseSizeFunc(text string) SizeFunc {
+	text = strings.Trim(text, " ")
+
+	for _, tag := range []string{"min", "max", "sum", "sub", "mul", "div", "clamp"} {
+		if strings.HasPrefix(text, tag) {
+			text = strings.Trim(strings.TrimPrefix(text, tag), " ")
+			last := len(text) - 1
+			if text[0] == '(' && text[last] == ')' {
+				text = text[1:last]
+				bracket := 0
+				start := 0
+				args := []any{}
+				for i, ch := range text {
+					switch ch {
+					case ',':
+						if bracket == 0 {
+							args = append(args, text[start:i])
+							start = i + 1
+						}
+
+					case '(':
+						bracket++
+
+					case ')':
+						bracket--
+					}
+				}
+				if bracket != 0 {
+					ErrorLogF(`Invalid "%s" function`, tag)
+					return nil
+				}
+
+				args = append(args, text[start:])
+				switch tag {
+				case "sub", "mul", "div":
+					if len(args) != 2 {
+						ErrorLogF(`"%s" function needs 2 arguments`, tag)
+						return nil
+					}
+				case "clamp":
+					if len(args) != 3 {
+						ErrorLog(`"clamp" function needs 3 arguments`)
+						return nil
+					}
+				}
+
+				data := new(sizeFuncData)
+				data.tag = tag
+				if data.parseArgs(args, tag == "mul" || tag == "div") {
+					return data
+				}
+			}
+
+			ErrorLogF(`Invalid "%s" function`, tag)
+			return nil
+		}
+	}
+
+	return nil
+}
+
+func (data *sizeFuncData) parseArgs(args []any, allowNumber bool) bool {
+	data.args = []any{}
+
+	numberArg := func(index int, value float64) bool {
+		if allowNumber {
+			if index == 1 {
+				if value == 0 && data.tag == "div" {
+					ErrorLog(`Division by 0 in div function`)
+					return false
+				}
+				data.args = append(data.args, value)
+				return true
+			} else {
+				ErrorLogF(`Only the second %s function argument can be a number`, data.tag)
+				return false
+			}
+		}
+
+		ErrorLogF(`The %s function argument cann't be a number`, data.tag)
+		return false
+	}
+
+	for i, arg := range args {
+		switch arg := arg.(type) {
+		case string:
+			if arg = strings.Trim(arg, " \t\n"); arg == "" {
+				ErrorLogF(`Unsupported %s function argument #%d: ""`, data.tag, i)
+				return false
+			}
+
+			if arg[0] == '@' {
+				data.args = append(data.args, arg)
+			} else if val, err := strconv.ParseFloat(arg, 64); err == nil {
+				return numberArg(i, val)
+			} else if fn := parseSizeFunc(arg); fn != nil {
+				data.args = append(data.args, fn)
+			} else if size, err := stringToSizeUnit(arg); err == nil {
+				data.args = append(data.args, size)
+			} else {
+				ErrorLogF(`Unsupported %s function argument #%d: "%s"`, data.tag, i, arg)
+				return false
+			}
+
+		case SizeFunc:
+			data.args = append(data.args, arg)
+
+		case SizeUnit:
+			if arg.Type == Auto {
+				ErrorLogF(`Unsupported %s function argument #%d: "auto"`, data.tag, i)
+			}
+			data.args = append(data.args, arg)
+
+		case float64:
+			return numberArg(i, arg)
+
+		case float32:
+			return numberArg(i, float64(arg))
+
+		default:
+			if n, ok := isInt(arg); ok {
+				return numberArg(i, float64(n))
+			}
+			ErrorLogF(`Unsupported %s function argument #%d: %v`, data.tag, i, arg)
+			return false
+		}
+	}
+	return true
+}
+
+func (data *sizeFuncData) String() string {
+	buffer := allocStringBuilder()
+	defer freeStringBuilder(buffer)
+
+	data.writeString("", buffer)
+	return buffer.String()
+}
+
+func (data *sizeFuncData) writeString(topFunc string, buffer *strings.Builder) {
+	buffer.WriteString(data.tag)
+	buffer.WriteRune('(')
+	for i, arg := range data.args {
+		if i > 0 {
+			buffer.WriteString(", ")
+		}
+		switch arg := arg.(type) {
+		case string:
+			buffer.WriteString(arg)
+
+		case SizeFunc:
+			arg.writeString(data.tag, buffer)
+
+		case SizeUnit:
+			buffer.WriteString(arg.String())
+
+		case fmt.Stringer:
+			buffer.WriteString(arg.String())
+
+		case float64:
+			buffer.WriteString(fmt.Sprintf("%g", arg))
+		}
+
+	}
+	buffer.WriteRune(')')
+}
+
+func (data *sizeFuncData) cssString(session Session) string {
+	buffer := allocStringBuilder()
+	defer freeStringBuilder(buffer)
+
+	data.writeCSS("", buffer, session)
+	return buffer.String()
+}
+
+func (data *sizeFuncData) writeCSS(topFunc string, buffer *strings.Builder, session Session) {
+	bracket := true
+	sep := ", "
+
+	mathFunc := func(s string) {
+		sep = s
+		switch topFunc {
+		case "":
+			buffer.WriteString("calc(")
+
+		case "min", "max", "clamp":
+			bracket = false
+
+		default:
+			buffer.WriteRune('(')
+		}
+	}
+
+	switch data.tag {
+	case "min", "max", "clamp":
+		buffer.WriteString(data.tag)
+		buffer.WriteRune('(')
+
+	case "sum":
+		mathFunc(" + ")
+
+	case "sub":
+		mathFunc(" - ")
+
+	case "mul":
+		mathFunc(" * ")
+
+	case "div":
+		mathFunc(" / ")
+
+	default:
+		return
+	}
+
+	for i, arg := range data.args {
+		if i > 0 {
+			buffer.WriteString(sep)
+		}
+		switch arg := arg.(type) {
+		case string:
+			if arg, ok := session.resolveConstants(arg); ok {
+				if fn := parseSizeFunc(arg); fn != nil {
+					fn.writeCSS(data.tag, buffer, session)
+				} else if size, err := stringToSizeUnit(arg); err == nil {
+					buffer.WriteString(size.cssString("0", session))
+				} else {
+					buffer.WriteString("0")
+				}
+			} else {
+				buffer.WriteString("0")
+			}
+
+		case SizeFunc:
+			arg.writeCSS(data.tag, buffer, session)
+
+		case SizeUnit:
+			buffer.WriteString(arg.cssString("0", session))
+
+		case fmt.Stringer:
+			buffer.WriteString(arg.String())
+
+		case float64:
+			buffer.WriteString(fmt.Sprintf("%g", arg))
+		}
+
+	}
+
+	if bracket {
+		buffer.WriteRune(')')
+	}
+}
+
+// MaxSize creates a SizeUnit function that calculates the maximum argument.
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc
+func MaxSize(arg0, arg1 any, args ...any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "max"
+	if !data.parseArgs(append([]any{arg0, arg1}, args...), false) {
+		return nil
+	}
+	return data
+}
+
+// MinSize creates a SizeUnit function that calculates the minimum argument.
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc.
+func MinSize(arg0, arg1 any, args ...any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "min"
+	if !data.parseArgs(append([]any{arg0, arg1}, args...), false) {
+		return nil
+	}
+	return data
+}
+
+// SumSize creates a SizeUnit function that calculates the sum of arguments.
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc.
+func SumSize(arg0, arg1 any, args ...any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "sum"
+	if !data.parseArgs(append([]any{arg0, arg1}, args...), false) {
+		return nil
+	}
+	return data
+}
+
+// SumSize creates a SizeUnit function that calculates the result of subtracting the arguments (arg1 - arg2).
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc.
+func SubSize(arg0, arg1 any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "sub"
+	if !data.parseArgs([]any{arg0, arg1}, false) {
+		return nil
+	}
+	return data
+}
+
+// MulSize creates a SizeUnit function that calculates the result of multiplying the arguments (arg1 * arg2).
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc.
+// The second argument can also be a number (float32, float32, int, int8...int64, uint, uint8...unit64)
+// or a string which is a text representation of a number.
+func MulSize(arg0, arg1 any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "mul"
+	if !data.parseArgs([]any{arg0, arg1}, true) {
+		return nil
+	}
+	return data
+}
+
+// DivSize creates a SizeUnit function that calculates the result of dividing the arguments (arg1 / arg2).
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc.
+// The second argument can also be a number (float32, float32, int, int8...int64, uint, uint8...unit64)
+// or a string which is a text representation of a number.
+func DivSize(arg0, arg1 any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "div"
+	if !data.parseArgs([]any{arg0, arg1}, true) {
+		return nil
+	}
+	return data
+}
+
+// ClampSize creates a SizeUnit function whose the result is calculated as follows:
+//
+//	min ≤ value ≤ max -> value;
+//	value < min -> min;
+//	max < value -> max;
+//
+// Valid argument types are SizeUnit, SizeFunc and a string which is a text description of SizeUnit or SizeFunc.
+func ClampSize(min, value, max any) SizeFunc {
+	data := new(sizeFuncData)
+	data.tag = "clamp"
+	if !data.parseArgs([]any{min, value, max}, false) {
+		return nil
+	}
+	return data
+}
diff --git a/sizeFunc_test.go b/sizeFunc_test.go
new file mode 100644
index 0000000..3b508a6
--- /dev/null
+++ b/sizeFunc_test.go
@@ -0,0 +1,50 @@
+package rui
+
+import (
+	"testing"
+)
+
+func TestSizeFunc(t *testing.T) {
+	session := new(sessionData)
+	session.getCurrentTheme().SetConstant("a1", "120px", "120px")
+
+	SetErrorLog(func(text string) {
+		t.Error(text)
+	})
+	SetDebugLog(func(text string) {
+		t.Log(text)
+	})
+
+	testFunc := func(fn SizeFunc, str, css string) {
+		if fn != nil {
+			if text := fn.String(); str != text {
+				t.Error("String() error.\nResult:   \"" + text + "\"\nExpected: \"" + str + `"`)
+			}
+			if text := fn.cssString(session); css != text {
+				t.Error("cssString() error.\nResult:   \"" + text + "\"\nExpected: \"" + css + `"`)
+			}
+		}
+	}
+
+	testFunc(MinSize("100%", Px(10)), `min(100%, 10px)`, `min(100%, 10px)`)
+	testFunc(MaxSize(Percent(100), "@a1"), `max(100%, @a1)`, `max(100%, 120px)`)
+	testFunc(SumSize(Percent(100), "@a1"), `sum(100%, @a1)`, `calc(100% + 120px)`)
+	testFunc(SubSize(Percent(100), "@a1"), `sub(100%, @a1)`, `calc(100% - 120px)`)
+	testFunc(MulSize(Percent(100), "@a1"), `mul(100%, @a1)`, `calc(100% * 120px)`)
+	testFunc(DivSize(Percent(100), "@a1"), `div(100%, @a1)`, `calc(100% / 120px)`)
+	testFunc(ClampSize(Percent(20), "@a1", Percent(40)), `clamp(20%, @a1, 40%)`, `clamp(20%, 120px, 40%)`)
+
+	testFunc(MaxSize(SubSize(Percent(100), "@a1"), "@a1"), `max(sub(100%, @a1), @a1)`, `max(100% - 120px, 120px)`)
+
+	testParse := func(str, css string) {
+		if fn := parseSizeFunc(str); fn != nil {
+			testFunc(fn, str, css)
+		}
+	}
+
+	testParse(`min(100%, 10px)`, `min(100%, 10px)`)
+	testParse(`max(100%, @a1)`, `max(100%, 120px)`)
+	testParse(`max(sub(100%, @a1), @a1)`, `max(100% - 120px, 120px)`)
+	testParse(`mul(sub(100%, @a1), @a1)`, `calc((100% - 120px) * 120px)`)
+	testParse(`mul(sub(100%, @a1), div(mul(@a1, 3), 2))`, `calc((100% - 120px) * ((120px * 3) / 2))`)
+}
diff --git a/sizeUnit.go b/sizeUnit.go
index 7e322ce..3106b63 100644
--- a/sizeUnit.go
+++ b/sizeUnit.go
@@ -14,89 +14,94 @@ import (
 type SizeUnitType uint8
 
 const (
-	// Auto - default value.
+	// Auto is the SizeUnit type: default value.
 	Auto SizeUnitType = 0
-	// SizeInPixel - size in pixels.
+	// SizeInPixel is the SizeUnit type: the Value field specifies the size in pixels.
 	SizeInPixel SizeUnitType = 1
-	// SizeInEM - size in em.
+	// SizeInEM is the SizeUnit type: the Value field specifies the size in em.
 	SizeInEM SizeUnitType = 2
-	// SizeInEX - size in em.
+	// SizeInEX is the SizeUnit type: the Value field specifies the size in em.
 	SizeInEX SizeUnitType = 3
-	// SizeInPercent - size in percents of a parant size.
+	// SizeInPercent is the SizeUnit type: the Value field specifies the size in percents of the parent size.
 	SizeInPercent SizeUnitType = 4
-	// SizeInPt - size in pt (1/72 inch).
+	// SizeInPt is the SizeUnit type: the Value field specifies the size in pt (1/72 inch).
 	SizeInPt SizeUnitType = 5
-	// SizeInPc - size in pc (1pc = 12pt).
+	// SizeInPc is the SizeUnit type: the Value field specifies the size in pc (1pc = 12pt).
 	SizeInPc SizeUnitType = 6
-	// SizeInInch - size in inches.
+	// SizeInInch is the SizeUnit type: the Value field specifies the size in inches.
 	SizeInInch SizeUnitType = 7
-	// SizeInMM - size in millimeters.
+	// SizeInMM is the SizeUnit type: the Value field specifies the size in millimeters.
 	SizeInMM SizeUnitType = 8
-	// SizeInCM - size in centimeters.
+	// SizeInCM is the SizeUnit type: the Value field specifies the size in centimeters.
 	SizeInCM SizeUnitType = 9
-	// SizeInFraction - size in fraction. Used only for "cell-width" and "cell-height" property
+	// SizeInFraction is the SizeUnit type: the Value field specifies the size in fraction.
+	// Used only for "cell-width" and "cell-height" property.
 	SizeInFraction SizeUnitType = 10
+	// SizeFunction is the SizeUnit type: the Function field specifies the size function.
+	// "min", "max", "clamp", "sum", "sub", "mul", and "div" functions are available.
+	SizeFunction = 11
 )
 
 // SizeUnit describe a size (Value field) and size unit (Type field).
 type SizeUnit struct {
-	Type  SizeUnitType
-	Value float64
+	Type     SizeUnitType
+	Value    float64
+	Function SizeFunc
 }
 
 // AutoSize creates SizeUnit with Auto type
 func AutoSize() SizeUnit {
-	return SizeUnit{Auto, 0}
+	return SizeUnit{Auto, 0, nil}
 }
 
 // Px creates SizeUnit with SizeInPixel type
 func Px(value float64) SizeUnit {
-	return SizeUnit{SizeInPixel, value}
+	return SizeUnit{SizeInPixel, value, nil}
 }
 
 // Em creates SizeUnit with SizeInEM type
 func Em(value float64) SizeUnit {
-	return SizeUnit{SizeInEM, value}
+	return SizeUnit{SizeInEM, value, nil}
 }
 
 // Ex creates SizeUnit with SizeInEX type
 func Ex(value float64) SizeUnit {
-	return SizeUnit{SizeInEX, value}
+	return SizeUnit{SizeInEX, value, nil}
 }
 
 // Percent creates SizeUnit with SizeInDIP type
 func Percent(value float64) SizeUnit {
-	return SizeUnit{SizeInPercent, value}
+	return SizeUnit{SizeInPercent, value, nil}
 }
 
 // Pt creates SizeUnit with SizeInPt type
 func Pt(value float64) SizeUnit {
-	return SizeUnit{SizeInPt, value}
+	return SizeUnit{SizeInPt, value, nil}
 }
 
 // Pc creates SizeUnit with SizeInPc type
 func Pc(value float64) SizeUnit {
-	return SizeUnit{SizeInPc, value}
+	return SizeUnit{SizeInPc, value, nil}
 }
 
 // Mm creates SizeUnit with SizeInMM type
 func Mm(value float64) SizeUnit {
-	return SizeUnit{SizeInMM, value}
+	return SizeUnit{SizeInMM, value, nil}
 }
 
 // Cm creates SizeUnit with SizeInCM type
 func Cm(value float64) SizeUnit {
-	return SizeUnit{SizeInCM, value}
+	return SizeUnit{SizeInCM, value, nil}
 }
 
 // Inch creates SizeUnit with SizeInInch type
 func Inch(value float64) SizeUnit {
-	return SizeUnit{SizeInInch, value}
+	return SizeUnit{SizeInInch, value, nil}
 }
 
 // Fr creates SizeUnit with SizeInFraction type
 func Fr(value float64) SizeUnit {
-	return SizeUnit{SizeInFraction, value}
+	return SizeUnit{SizeInFraction, value, nil}
 }
 
 // Equal compare two SizeUnit. Return true if SizeUnit are equal
@@ -152,7 +157,7 @@ func stringToSizeUnit(value string) (SizeUnit, error) {
 		}
 	}
 
-	if val, err := strconv.ParseFloat(value, 64); err != nil {
+	if val, err := strconv.ParseFloat(value, 64); err == nil {
 		return SizeUnit{Type: SizeInPixel, Value: val}, nil
 	}
 
@@ -161,8 +166,15 @@ func stringToSizeUnit(value string) (SizeUnit, error) {
 
 // String - convert SizeUnit to string
 func (size SizeUnit) String() string {
-	if size.Type == Auto {
+	switch size.Type {
+	case Auto:
 		return "auto"
+
+	case SizeFunction:
+		if size.Function == nil {
+			return "auto"
+		}
+		return size.Function.String()
 	}
 	if suffix, ok := sizeUnitSuffixes()[size.Type]; ok {
 		return fmt.Sprintf("%g%s", size.Value, suffix)
@@ -171,13 +183,19 @@ func (size SizeUnit) String() string {
 }
 
 // cssString - convert SizeUnit to string
-func (size SizeUnit) cssString(textForAuto string) string {
+func (size SizeUnit) cssString(textForAuto string, session Session) string {
 	switch size.Type {
 	case Auto:
 		return textForAuto
 
 	case SizeInEM:
 		return fmt.Sprintf("%grem", size.Value)
+
+	case SizeFunction:
+		if size.Function == nil {
+			return textForAuto
+		}
+		return size.Function.cssString(session)
 	}
 
 	if size.Value == 0 {
diff --git a/tableView.go b/tableView.go
index bd979ff..49151d2 100644
--- a/tableView.go
+++ b/tableView.go
@@ -594,7 +594,7 @@ func (table *tableViewData) propertyChanged(tag string) {
 				updateCSSProperty(htmlID, "border-spacing", "0", session)
 				updateCSSProperty(htmlID, "border-collapse", "collapse", session)
 			} else {
-				updateCSSProperty(htmlID, "border-spacing", gap.cssString("0"), session)
+				updateCSSProperty(htmlID, "border-spacing", gap.cssString("0", session), session)
 				updateCSSProperty(htmlID, "border-collapse", "separate", session)
 			}
 
@@ -1319,24 +1319,26 @@ func (table *tableViewData) getCurrent() CellIndex {
 }
 
 func (table *tableViewData) cssStyle(self View, builder cssBuilder) {
-	table.viewData.cssViewStyle(builder, table.Session())
+	session := table.Session()
+	table.viewData.cssViewStyle(builder, session)
 
-	gap, ok := sizeProperty(table, Gap, table.Session())
+	gap, ok := sizeProperty(table, Gap, session)
 	if !ok || gap.Type == Auto || gap.Value <= 0 {
 		builder.add("border-spacing", "0")
 		builder.add("border-collapse", "collapse")
 	} else {
-		builder.add("border-spacing", gap.cssString("0"))
+		builder.add("border-spacing", gap.cssString("0", session))
 		builder.add("border-collapse", "separate")
 	}
 }
 
 func (table *tableViewData) ReloadTableData() {
+	session := table.Session()
 	if content := table.content(); content != nil {
-		updateProperty(table.htmlID(), "data-rows", strconv.Itoa(content.RowCount()), table.Session())
-		updateProperty(table.htmlID(), "data-columns", strconv.Itoa(content.ColumnCount()), table.Session())
+		updateProperty(table.htmlID(), "data-rows", strconv.Itoa(content.RowCount()), session)
+		updateProperty(table.htmlID(), "data-columns", strconv.Itoa(content.ColumnCount()), session)
 	}
-	updateInnerHTML(table.htmlID(), table.Session())
+	updateInnerHTML(table.htmlID(), session)
 }
 
 func (table *tableViewData) onItemResize(self View, index string, x, y, width, height float64) {
diff --git a/view.go b/view.go
index 9df58ab..c29a8cb 100644
--- a/view.go
+++ b/view.go
@@ -446,7 +446,7 @@ func viewPropertyChanged(view *viewData, tag string) {
 		return
 
 	case Outline, OutlineColor, OutlineStyle, OutlineWidth:
-		updateCSSProperty(htmlID, Outline, GetOutline(view).cssString(), session)
+		updateCSSProperty(htmlID, Outline, GetOutline(view).cssString(session), session)
 		return
 
 	case Shadow:
@@ -462,19 +462,19 @@ func viewPropertyChanged(view *viewData, tag string) {
 		RadiusBottomLeft, RadiusBottomLeftX, RadiusBottomLeftY,
 		RadiusBottomRight, RadiusBottomRightX, RadiusBottomRightY:
 		radius := GetRadius(view)
-		updateCSSProperty(htmlID, "border-radius", radius.cssString(), session)
+		updateCSSProperty(htmlID, "border-radius", radius.cssString(session), session)
 		return
 
 	case Margin, MarginTop, MarginRight, MarginBottom, MarginLeft,
 		"top-margin", "right-margin", "bottom-margin", "left-margin":
 		margin := GetMargin(view)
-		updateCSSProperty(htmlID, Margin, margin.cssString(), session)
+		updateCSSProperty(htmlID, Margin, margin.cssString(session), session)
 		return
 
 	case Padding, PaddingTop, PaddingRight, PaddingBottom, PaddingLeft,
 		"top-padding", "right-padding", "bottom-padding", "left-padding":
 		padding := GetPadding(view)
-		updateCSSProperty(htmlID, Padding, padding.cssString(), session)
+		updateCSSProperty(htmlID, Padding, padding.cssString(session), session)
 		return
 
 	case AvoidBreak:
@@ -626,7 +626,7 @@ func viewPropertyChanged(view *viewData, tag string) {
 
 	if cssTag, ok := sizeProperties[tag]; ok {
 		size, _ := sizeProperty(view, tag, session)
-		updateCSSProperty(htmlID, cssTag, size.cssString(""), session)
+		updateCSSProperty(htmlID, cssTag, size.cssString("", session), session)
 		return
 	}
 
diff --git a/viewClip.go b/viewClip.go
index 2f61010..d8074ea 100644
--- a/viewClip.go
+++ b/viewClip.go
@@ -146,13 +146,13 @@ func (clip *insetClip) cssStyle(session Session) string {
 	for _, tag := range []string{Top, Right, Bottom, Left} {
 		value, _ := sizeProperty(clip, tag, session)
 		buffer.WriteString(leadText)
-		buffer.WriteString(value.cssString("0px"))
+		buffer.WriteString(value.cssString("0px", session))
 		leadText = " "
 	}
 
 	if radius := getRadiusProperty(clip); radius != nil {
 		buffer.WriteString(" round ")
-		buffer.WriteString(radius.BoxRadius(session).cssString())
+		buffer.WriteString(radius.BoxRadius(session).cssString(session))
 	}
 
 	buffer.WriteRune(')')
@@ -211,15 +211,15 @@ func (clip *circleClip) cssStyle(session Session) string {
 
 	buffer.WriteString("circle(")
 	r, _ := sizeProperty(clip, Radius, session)
-	buffer.WriteString(r.cssString("50%"))
+	buffer.WriteString(r.cssString("50%", session))
 
 	buffer.WriteString(" at ")
 	x, _ := sizeProperty(clip, X, session)
-	buffer.WriteString(x.cssString("50%"))
+	buffer.WriteString(x.cssString("50%", session))
 	buffer.WriteRune(' ')
 
 	y, _ := sizeProperty(clip, Y, session)
-	buffer.WriteString(y.cssString("50%"))
+	buffer.WriteString(y.cssString("50%", session))
 	buffer.WriteRune(')')
 
 	return buffer.String()
@@ -280,17 +280,17 @@ func (clip *ellipseClip) cssStyle(session Session) string {
 	rx, _ := sizeProperty(clip, RadiusX, session)
 	ry, _ := sizeProperty(clip, RadiusX, session)
 	buffer.WriteString("ellipse(")
-	buffer.WriteString(rx.cssString("50%"))
+	buffer.WriteString(rx.cssString("50%", session))
 	buffer.WriteRune(' ')
-	buffer.WriteString(ry.cssString("50%"))
+	buffer.WriteString(ry.cssString("50%", session))
 
 	buffer.WriteString(" at ")
 	x, _ := sizeProperty(clip, X, session)
-	buffer.WriteString(x.cssString("50%"))
+	buffer.WriteString(x.cssString("50%", session))
 	buffer.WriteRune(' ')
 
 	y, _ := sizeProperty(clip, Y, session)
-	buffer.WriteString(y.cssString("50%"))
+	buffer.WriteString(y.cssString("50%", session))
 	buffer.WriteRune(')')
 
 	return buffer.String()
@@ -427,13 +427,13 @@ func (clip *polygonClip) cssStyle(session Session) string {
 		case string:
 			if val, ok := session.resolveConstants(value); ok {
 				if size, ok := StringToSizeUnit(val); ok {
-					buffer.WriteString(size.cssString("0px"))
+					buffer.WriteString(size.cssString("0px", session))
 					return
 				}
 			}
 
 		case SizeUnit:
-			buffer.WriteString(value.cssString("0px"))
+			buffer.WriteString(value.cssString("0px", session))
 			return
 		}
 
diff --git a/viewStyle.go b/viewStyle.go
index f09aa54..4adecdc 100644
--- a/viewStyle.go
+++ b/viewStyle.go
@@ -173,11 +173,11 @@ func (style *viewStyle) backgroundCSS(session Session) string {
 func (style *viewStyle) cssViewStyle(builder cssBuilder, session Session) {
 
 	if margin, ok := boundsProperty(style, Margin, session); ok {
-		margin.cssValue(Margin, builder)
+		margin.cssValue(Margin, builder, session)
 	}
 
 	if padding, ok := boundsProperty(style, Padding, session); ok {
-		padding.cssValue(Padding, builder)
+		padding.cssValue(Padding, builder, session)
 	}
 
 	if border := getBorder(style, Border); border != nil {
@@ -187,10 +187,10 @@ func (style *viewStyle) cssViewStyle(builder cssBuilder, session Session) {
 	}
 
 	radius := getRadius(style, session)
-	radius.cssValue(builder)
+	radius.cssValue(builder, session)
 
 	if outline := getOutline(style); outline != nil {
-		outline.ViewOutline(session).cssValue(builder)
+		outline.ViewOutline(session).cssValue(builder, session)
 	}
 
 	if z, ok := intProperty(style, ZIndex, session, 0); ok {
@@ -215,7 +215,7 @@ func (style *viewStyle) cssViewStyle(builder cssBuilder, session Session) {
 			if !ok {
 				cssTag = tag
 			}
-			builder.add(cssTag, size.cssString(""))
+			builder.add(cssTag, size.cssString("", session))
 		}
 	}
 
diff --git a/viewTransform.go b/viewTransform.go
index 6625c19..d13f03a 100644
--- a/viewTransform.go
+++ b/viewTransform.go
@@ -125,11 +125,11 @@ func (style *viewStyle) transform(session Session) string {
 				buffer.WriteRune(' ')
 			}
 			buffer.WriteString(`translate3d(`)
-			buffer.WriteString(x.cssString("0"))
+			buffer.WriteString(x.cssString("0", session))
 			buffer.WriteRune(',')
-			buffer.WriteString(y.cssString("0"))
+			buffer.WriteString(y.cssString("0", session))
 			buffer.WriteRune(',')
-			buffer.WriteString(z.cssString("0"))
+			buffer.WriteString(z.cssString("0", session))
 			buffer.WriteRune(')')
 		}
 
@@ -172,9 +172,9 @@ func (style *viewStyle) transform(session Session) string {
 				buffer.WriteRune(' ')
 			}
 			buffer.WriteString(`translate(`)
-			buffer.WriteString(x.cssString("0"))
+			buffer.WriteString(x.cssString("0", session))
 			buffer.WriteRune(',')
-			buffer.WriteString(y.cssString("0"))
+			buffer.WriteString(y.cssString("0", session))
 			buffer.WriteRune(')')
 		}
 
@@ -205,12 +205,12 @@ func (style *viewStyle) transform(session Session) string {
 func (style *viewStyle) writeViewTransformCSS(builder cssBuilder, session Session) {
 	if getTransform3D(style, session) {
 		if perspective, ok := sizeProperty(style, Perspective, session); ok && perspective.Type != Auto && perspective.Value != 0 {
-			builder.add(`perspective`, perspective.cssString("0"))
+			builder.add(`perspective`, perspective.cssString("0", session))
 		}
 
 		x, y := getPerspectiveOrigin(style, session)
 		if x.Type != Auto || y.Type != Auto {
-			builder.addValues(`perspective-origin`, ` `, x.cssString("50%"), y.cssString("50%"))
+			builder.addValues(`perspective-origin`, ` `, x.cssString("50%", session), y.cssString("50%", session))
 		}
 
 		if backfaceVisible, ok := boolProperty(style, BackfaceVisible, session); ok {
@@ -223,12 +223,12 @@ func (style *viewStyle) writeViewTransformCSS(builder cssBuilder, session Sessio
 
 		x, y, z := getOrigin(style, session)
 		if x.Type != Auto || y.Type != Auto || z.Type != Auto {
-			builder.addValues(`transform-origin`, ` `, x.cssString("50%"), y.cssString("50%"), z.cssString("0"))
+			builder.addValues(`transform-origin`, ` `, x.cssString("50%", session), y.cssString("50%", session), z.cssString("0", session))
 		}
 	} else {
 		x, y, _ := getOrigin(style, session)
 		if x.Type != Auto || y.Type != Auto {
-			builder.addValues(`transform-origin`, ` `, x.cssString("50%"), y.cssString("50%"))
+			builder.addValues(`transform-origin`, ` `, x.cssString("50%", session), y.cssString("50%", session))
 		}
 	}
 
@@ -248,7 +248,7 @@ func (view *viewData) updateTransformProperty(tag string) bool {
 			x, y := GetPerspectiveOrigin(view)
 			value := ""
 			if x.Type != Auto || y.Type != Auto {
-				value = x.cssString("50%") + " " + y.cssString("50%")
+				value = x.cssString("50%", session) + " " + y.cssString("50%", session)
 			}
 			updateCSSProperty(htmlID, "perspective-origin", value, session)
 		}
@@ -267,11 +267,11 @@ func (view *viewData) updateTransformProperty(tag string) bool {
 		value := ""
 		if getTransform3D(view, session) {
 			if x.Type != Auto || y.Type != Auto || z.Type != Auto {
-				value = x.cssString("50%") + " " + y.cssString("50%") + " " + z.cssString("50%")
+				value = x.cssString("50%", session) + " " + y.cssString("50%", session) + " " + z.cssString("50%", session)
 			}
 		} else {
 			if x.Type != Auto || y.Type != Auto {
-				value = x.cssString("50%") + " " + y.cssString("50%")
+				value = x.cssString("50%", session) + " " + y.cssString("50%", session)
 			}
 		}
 		updateCSSProperty(htmlID, "transform-origin", value, session)