Fix #261: Show next-up sort icon when hovering over sortable list header

ui/theme/themedrectangle.go

@@ -1,17 +1,22 @@
 package theme
 
 import (
+	"image/color"
+
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/canvas"
 	"fyne.io/fyne/v2/widget"
 )
 
+const translucentAlpha = 155
+
 type ThemedRectangle struct {
 	widget.BaseWidget
 
 	rect *canvas.Rectangle
 
 	ColorName       fyne.ThemeColorName
+	Translucent     bool
 	BorderWidth     float32
 	BorderColorName fyne.ThemeColorName
 }
@@ -29,7 +34,12 @@ func NewThemedRectangle(colorName fyne.ThemeColorName) *ThemedRectangle {
 func (t *ThemedRectangle) Refresh() {
 	settings := fyne.CurrentApp().Settings()
 	theme := settings.Theme()
-	t.rect.FillColor = theme.Color(t.ColorName, settings.ThemeVariant())
+	fc := theme.Color(t.ColorName, settings.ThemeVariant())
+	if t.Translucent {
+		r, g, b, _ := fc.RGBA()
+		fc = color.NRGBA{R: uint8(r), G: uint8(g), B: uint8(b), A: translucentAlpha}
+	}
+	t.rect.FillColor = fc
 	t.rect.StrokeWidth = t.BorderWidth
 	t.rect.StrokeColor = theme.Color(t.BorderColorName, settings.ThemeVariant())
 	t.BaseWidget.Refresh()