Canvas: add #restoreContextAfterPaintAlpha:with:

src/Alexandrie-Canvas/AeCanvas.class.st

@@ -609,6 +609,20 @@ AeCanvas >> restoreContextAfter: aBlock [
 	cairoContext restoreStateAfter: aBlock
 ]
 
+{ #category : #'API - state' }
+AeCanvas >> restoreContextAfterPaintAlpha: opacity with: aBlock [
+	"Evaluate a block to paint with certain opacity (a value in 0.0 to 1.0 interval).
+	* When opacity is translucent (less than 1.0), then the paint operation in the block
+	closure will be performed into a 'Cairo group' (a kind of temporary surface) that
+	will be finally painted with such opacity.
+	* When opacity is 1.0, then do it more efficiently: paint directly on the target surface,
+	using Cairo save and restore to keep the Cairo context state untouched on return."
+
+	opacity < 1.0
+		ifTrue: [ self paintGroupWith: aBlock alpha: opacity ]
+		ifFalse: [ self restoreContextAfter: aBlock ]
+]
+
 { #category : #private }
 AeCanvas >> restoreContextOnlyIfClipAfterwards: aBlock [