Merge pull request #270 from UnityTech/antialias

Fix transparent color issue.

Runtime/Resources/UIWidgets_canvas.cginc

 }
 
 fixed4 frag_stroke_alpha(v2f i) : SV_Target {
-    return shader_color(i) * strokeMask(i.ftcoord.x, i.ftcoord.y);
+    return prealpha(shader_color(i)) * strokeMask(i.ftcoord.x, i.ftcoord.y);
 }