Added "image constants"

background.go

@@ -239,7 +239,7 @@ func (image *backgroundImage) Get(tag string) interface{} {
 }
 
 func (image *backgroundImage) cssStyle(session Session) string {
-	if src, ok := stringProperty(image, Source, session); ok && src != "" {
+	if src, ok := imageProperty(image, Source, session); ok && src != "" {
 		buffer := allocStringBuilder()
 		defer freeStringBuilder(buffer)
 

image.go

@@ -128,5 +128,10 @@ func (manager *imageManager) imageLoadError(obj DataObject, session Session) {
 
 // LoadImage starts the async image loading by url
 func LoadImage(url string, onLoaded func(Image), session Session) Image {
+	if url != "" && url[0] == '@' {
+		if image, ok := session.ImageConstant(url[1:]); ok {
+			url = image
+		}
+	}
 	return session.imageManager().loadImage(url, onLoaded, session)
 }

imageView.go

@@ -109,8 +109,12 @@ func (imageView *imageViewData) set(tag string, value interface{}) bool {
 		if text, ok := value.(string); ok {
 			imageView.properties[Source] = text
 			if imageView.created {
-				updateProperty(imageView.htmlID(), "src", text, imageView.session)
+				src := text
-				if srcset := imageView.srcSet(text); srcset != "" {
+				if src != "" && src[0] == '@' {
+					src, _ = imageProperty(imageView, Source, imageView.session)
+				}
+				updateProperty(imageView.htmlID(), "src", src, imageView.session)
+				if srcset := imageView.srcSet(src); srcset != "" {
 					updateProperty(imageView.htmlID(), "srcset", srcset, imageView.session)
 				} else {
 					removeProperty(imageView.htmlID(), "srcset", imageView.session)
@@ -179,15 +183,25 @@ func (imageView *imageViewData) closeHTMLTag() bool {
 
 func (imageView *imageViewData) htmlProperties(self View, buffer *strings.Builder) {
 	imageView.viewData.htmlProperties(self, buffer)
-	imageResource := GetImageViewSource(imageView, "")
+
-	if imageResource != "" {
+	if imageResource, ok := imageProperty(imageView, Source, imageView.Session()); ok && imageResource != "" {
-		buffer.WriteString(` src="`)
+		if imageResource[0] == '@' {
-		buffer.WriteString(imageResource)
+			if image, ok := imageView.Session().ImageConstant(imageResource[1:]); ok {
-		buffer.WriteString(`"`)
+				imageResource = image
-		if srcset := imageView.srcSet(imageResource); srcset != "" {
+			} else {
-			buffer.WriteString(` srcset="`)
+				imageResource = ""
-			buffer.WriteString(srcset)
+			}
+		}
+
+		if imageResource != "" {
+			buffer.WriteString(` src="`)
+			buffer.WriteString(imageResource)
 			buffer.WriteString(`"`)
+			if srcset := imageView.srcSet(imageResource); srcset != "" {
+				buffer.WriteString(` srcset="`)
+				buffer.WriteString(srcset)
+				buffer.WriteString(`"`)
+			}
 		}
 	}
 
@@ -236,9 +250,16 @@ func (imageView *imageViewData) cssStyle(self View, builder cssBuilder) {
 // GetImageViewSource returns the image URL of an ImageView subview.
 // If the second argument (subviewID) is "" then a left position of the first argument (view) is returned
 func GetImageViewSource(view View, subviewID string) string {
-	if image, ok := stringProperty(view, Source, view.Session()); ok {
+	if subviewID != "" {
-		return image
+		view = ViewByID(view, subviewID)
 	}
+
+	if view != nil {
+		if image, ok := imageProperty(view, Source, view.Session()); ok {
+			return image
+		}
+	}
+
 	return ""
 }
 

propertyGet.go

@@ -14,6 +14,23 @@ func stringProperty(properties Properties, tag string, session Session) (string,
 	return "", false
 }
 
+func imageProperty(properties Properties, tag string, session Session) (string, bool) {
+	if value := properties.getRaw(tag); value != nil {
+		if text, ok := value.(string); ok {
+			if text != "" && text[0] == '@' {
+				if image, ok := session.ImageConstant(text[1:]); ok {
+					return image, true
+				} else {
+					return "", false
+				}
+			}
+
+			return text, true
+		}
+	}
+	return "", false
+}
+
 func valueToSizeUnit(value interface{}, session Session) (SizeUnit, bool) {
 	if value != nil {
 		switch value := value.(type) {

resources.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -422,5 +423,6 @@ func AllImageResources() []string {
 	for image := range resources.images {
 		result = append(result, image)
 	}
+	sort.Strings(result)
 	return result
 }

session.go

@@ -35,6 +35,10 @@ type Session interface {
 	Color(tag string) (Color, bool)
 	// ColorTags returns the list of all available color constants
 	ColorTags() []string
+	// ImageConstant returns the image constant with "tag" name or "" if it is not exists
+	ImageConstant(tag string) (string, bool)
+	// ImageConstantTags returns the list of all available image constants
+	ImageConstantTags() []string
 	// SetCustomTheme set the custom theme
 	SetCustomTheme(name string) bool
 	// UserAgent returns the "user-agent" text of the client browser

sessionTheme.go

@@ -186,6 +186,45 @@ func (session *sessionData) Color(tag string) (Color, bool) {
 	}
 }
 
+func (session *sessionData) ImageConstant(tag string) (string, bool) {
+	tags := []string{tag}
+	result := ""
+	theme := session.getCurrentTheme()
+	for {
+		ok := false
+		if session.darkTheme {
+			if theme.darkImages != nil {
+				result, ok = theme.darkImages[tag]
+			}
+		}
+
+		if !ok {
+			if theme.images != nil {
+				result, ok = theme.images[tag]
+			}
+		}
+
+		if !ok {
+			ErrorLogF(`"%v" image not found`, tag)
+			return "", false
+		}
+
+		if result == "" || result[0] != '@' {
+			return result, true
+		}
+
+		tag = result[1:]
+		for _, t := range tags {
+			if t == tag {
+				ErrorLogF(`"%v" image is cyclic`, tag)
+				return "", false
+			}
+		}
+
+		tags = append(tags, tag)
+	}
+}
+
 func (session *sessionData) SetCustomTheme(name string) bool {
 	if name == "" {
 		if session.customTheme == nil {
@@ -374,3 +413,21 @@ func (session *sessionData) ColorTags() []string {
 	sort.Strings(keys)
 	return keys
 }
+
+func (session *sessionData) ImageConstantTags() []string {
+	theme := session.getCurrentTheme()
+
+	keys := make([]string, 0, len(theme.colors))
+	for k := range theme.images {
+		keys = append(keys, k)
+	}
+
+	for tag := range theme.darkImages {
+		if _, ok := theme.images[tag]; !ok {
+			keys = append(keys, tag)
+		}
+	}
+
+	sort.Strings(keys)
+	return keys
+}

theme.go

@@ -111,6 +111,8 @@ type theme struct {
 	touchConstants map[string]string
 	colors         map[string]string
 	darkColors     map[string]string
+	images         map[string]string
+	darkImages     map[string]string
 	styles         map[string]Params
 	mediaStyles    []mediaStyle
 }
@@ -129,6 +131,8 @@ func (theme *theme) init() {
 	theme.touchConstants = map[string]string{}
 	theme.colors = map[string]string{}
 	theme.darkColors = map[string]string{}
+	theme.images = map[string]string{}
+	theme.darkImages = map[string]string{}
 	theme.styles = map[string]Params{}
 	theme.mediaStyles = []mediaStyle{}
 }
@@ -154,6 +158,14 @@ func (theme *theme) concat(anotherTheme *theme) {
 		theme.darkColors[tag] = color
 	}
 
+	for tag, image := range anotherTheme.images {
+		theme.images[tag] = image
+	}
+
+	for tag, image := range anotherTheme.darkImages {
+		theme.darkImages[tag] = image
+	}
+
 	for tag, style := range anotherTheme.styles {
 		theme.styles[tag] = style
 	}
@@ -308,6 +320,30 @@ func (theme *theme) parseThemeData(data DataObject) {
 					}
 				}
 
+			case "images":
+				if d.Type() == ObjectNode {
+					if obj := d.Object(); obj != nil {
+						objCount := obj.PropertyCount()
+						for k := 0; k < objCount; k++ {
+							if prop := obj.Property(k); prop != nil && prop.Type() == TextNode {
+								theme.images[prop.Tag()] = prop.Text()
+							}
+						}
+					}
+				}
+
+			case "images:dark":
+				if d.Type() == ObjectNode {
+					if obj := d.Object(); obj != nil {
+						objCount := obj.PropertyCount()
+						for k := 0; k < objCount; k++ {
+							if prop := obj.Property(k); prop != nil && prop.Type() == TextNode {
+								theme.darkImages[prop.Tag()] = prop.Text()
+							}
+						}
+					}
+				}
+
 			case "styles":
 				if d.Type() == ArrayNode {
 					arraySize := d.ArraySize()