[[ Graphics ]] Paint Opacity

runrevmark · runrevmark · commit d0da592cb901 · 2017-11-24T08:33:30.000Z
This patch implements the currently unimplemented fill and
stroke opacity properties.

The fill and stroke opacity differ from opacity in that they
are applied as attenuations on the pixels generated by the
paint, rather than acting as a mask for composition to the
target surface.

In Skia, paints which use shaders take the opacity from the
alpha of the color which is set on the SkPaint. For colors,
the alpha value must be multipled by the opacity.
diff --git a/libgraphics/src/context.cpp b/libgraphics/src/context.cpp
@@ -120,14 +120,14 @@ static bool MCGContextStateCreate(MCGContextStateRef& r_state)
 		t_state -> should_antialias = false;
 		
 		t_state -> fill_color = MCGColorMakeRGBA(0.0f, 0.0f, 0.0f, 1.0f);
-		t_state -> fill_opacity = 0.0f;
+		t_state -> fill_opacity = 1.0f;
 		t_state -> fill_rule = kMCGFillRuleNonZero;
 		t_state -> fill_pattern = NULL;
 		t_state -> fill_gradient= NULL;
 		t_state -> fill_style = kMCGPaintStyleOpaque;
 		
 		t_state -> stroke_color = MCGColorMakeRGBA(0.0f, 0.0f, 0.0f, 1.0f);
-		t_state -> stroke_opacity = 0.0f;
+		t_state -> stroke_opacity = 1.0f;
 		t_state -> stroke_pattern = NULL;
 		t_state -> stroke_gradient= NULL;
 		t_state -> stroke_attr . width = 0.0f;
@@ -2029,7 +2029,7 @@ void MCGContextAddPath(MCGContextRef self, MCGPathRef p_path)
 ////////////////////////////////////////////////////////////////////////////////
 // Paint setup
 
-static bool MCGContextApplyPaintSettingsToSkPaint(MCGContextRef self, MCGColor p_color, MCGPatternRef p_pattern, MCGGradientRef p_gradient, MCGPaintStyle p_paint_style, SkPaint &r_paint)
+static bool MCGContextApplyPaintSettingsToSkPaint(MCGContextRef self, MCGFloat p_opacity, MCGColor p_color, MCGPatternRef p_pattern, MCGGradientRef p_gradient, MCGPaintStyle p_paint_style, SkPaint &r_paint)
 {
 	// TODO: Refactor color, pattern and gradients into ref counted (copy on write?) paint type.
 	bool t_success;
@@ -2076,11 +2076,20 @@ static bool MCGContextApplyPaintSettingsToSkPaint(MCGContextRef self, MCGColor p
 	
 	if (t_success)
 	{
-		// Don't set the paint color if using a shader, as the color's alpha value will be applied to the paint (which we don't want to happen!).
+		// Set the shader or solid color here - the opacity for a shader is taken
+        // from the Alpha channel of the solid color; but for solid colors we
+        // must multiply the solid color's alpha by the provided alpha.
 		if (t_shader != nil)
+        {
 			r_paint . setShader(t_shader);
+			r_paint . setAlpha((U8CPU)(p_opacity * 255));
+        }
 		else
+        {
 			r_paint . setColor(MCGColorToSkColor(p_color));
+            r_paint . setAlpha((U8CPU)(r_paint.getAlpha() * p_opacity));
+        }
+        
 		r_paint . setMaskFilter(t_stipple);
 		
         // MM-2014-01-09: [[ LibSkiaUpdate ]] Updated filters to use Skia's new filter levels.
@@ -2110,7 +2119,7 @@ static bool MCGContextSetupFillPaint(MCGContextRef self, SkPaint &r_paint)
 	t_success = true;
 	
 	if (t_success)
-		t_success = MCGContextApplyPaintSettingsToSkPaint(self, self -> state -> fill_color, self -> state -> fill_pattern, self -> state -> fill_gradient, self -> state -> fill_style, r_paint);
+		t_success = MCGContextApplyPaintSettingsToSkPaint(self, self -> state -> fill_opacity, self -> state -> fill_color, self -> state -> fill_pattern, self -> state -> fill_gradient, self -> state -> fill_style, r_paint);
 	
 	if (t_success)
 	{		
@@ -2128,7 +2137,7 @@ static bool MCGContextSetupStrokePaint(MCGContextRef self, SkPaint &r_paint)
 	t_success = true;
 	
 	if (t_success)
-		t_success = MCGContextApplyPaintSettingsToSkPaint(self, self -> state -> stroke_color, self -> state -> stroke_pattern, self -> state -> stroke_gradient, self -> state -> stroke_style, r_paint);
+		t_success = MCGContextApplyPaintSettingsToSkPaint(self, self -> state -> stroke_opacity, self -> state -> stroke_color, self -> state -> stroke_pattern, self -> state -> stroke_gradient, self -> state -> stroke_style, r_paint);
 	
 	sk_sp<SkPathEffect> t_dash_effect;
 	if (t_success)
