[[ Bug 19675 ]] Disable LCD text rendering when backing layer is not opaque

livecodeian · livecodeian · commit 6c069dae5aa0 · 2017-05-22T11:38:04.000+01:00
diff --git a/libgraphics/include/graphics.h b/libgraphics/include/graphics.h
@@ -885,6 +885,9 @@ uint32_t MCGContextGetHeight(MCGContextRef context);
 // invalid and all further operations will be no-ops.
 bool MCGContextIsValid(MCGContextRef context);
 
+// Returns whether the current context layer is fully opaque or contains a transparency channel.
+bool MCGContextIsLayerOpaque(MCGContextRef context);
+
 // Graphics state operations
 void MCGContextSave(MCGContextRef context);
 void MCGContextRestore(MCGContextRef context);
diff --git a/libgraphics/src/context.cpp b/libgraphics/src/context.cpp
@@ -572,6 +572,11 @@ bool MCGContextIsValid(MCGContextRef self)
 	return self != NULL && self -> is_valid;
 }
 
+bool MCGContextIsLayerOpaque(MCGContextRef self)
+{
+	return SkAlphaTypeIsOpaque(self->layer->canvas->imageInfo().alphaType());
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Graphics state operations
 
diff --git a/libgraphics/src/directwrite-skia.cpp b/libgraphics/src/directwrite-skia.cpp
@@ -379,6 +379,10 @@ void MCGContextDrawPlatformText(MCGContextRef self, const unichar_t *p_text, uin
 			t_paint.setColor(MCGColorToSkColor(self->state->fill_color));
 			t_paint.setBlendMode(MCGBlendModeToSkBlendMode(self->state->blend_mode));
 
+			// disable LCD rendering when backing layer may be transparent
+			if (!MCGContextIsLayerOpaque(self))
+				t_paint.setLCDRenderText(false);
+
 			// Force anti-aliasing on so that we get nicely-rendered text
 			t_paint.setAntiAlias(true);
 
