From a5fdc07fcace0ad95e83c67dc363b2e5facdba84 Mon Sep 17 00:00:00 2001
From: James Chen <jianhua.chen@cocos2d-x.org>
Date: Wed, 19 Oct 2016 10:19:14 +0800
Subject: [PATCH] Fixes label wrong blending and improves performance while
 enabling outline. (#16717)

---
 cocos/renderer/ccShader_Label_outline.frag | 27 +++++++++++++++++-----
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/cocos/renderer/ccShader_Label_outline.frag b/cocos/renderer/ccShader_Label_outline.frag
index 3b01c0a365..c4d8311225 100644
--- a/cocos/renderer/ccShader_Label_outline.frag
+++ b/cocos/renderer/ccShader_Label_outline.frag
@@ -15,13 +15,28 @@ uniform vec4 u_textColor;
 void main()
 {
     vec4 sample = texture2D(CC_Texture0, v_texCoord);
-    float fontAlpha = sample.a; 
-    float outlineAlpha = sample.r; 
-    if ((fontAlpha + outlineAlpha) > 0.0){
-        vec4 color = u_textColor * fontAlpha + u_effectColor * (1.0 - fontAlpha);
-        gl_FragColor = v_fragmentColor * vec4( color.rgb,max(fontAlpha,outlineAlpha)*color.a);
+    float fontAlpha = sample.a; // sample.a == 1 indicates text, a == 0 indicates outline 
+    float outlineAlpha = sample.r; // sample.r always > 0
+
+    if (u_effectColor.a > 0.0) // draw outline
+    {
+        if (fontAlpha < 1.0)
+        {
+            gl_FragColor = v_fragmentColor * vec4(u_effectColor.rgb, u_effectColor.a * outlineAlpha);
+        }
+        else
+        {
+            discard; // While drawing outline, text should not be drawn since it will be drawn in next step.
+                     // discard this pixel could improve a little and fix wrong alpha blending if text contains
+                     // alpha channel.
+        }
     }
-    else {
+    else if (fontAlpha > 0.0) // draw text
+    {
+        gl_FragColor = v_fragmentColor * vec4(u_textColor.rgb, u_textColor.a * fontAlpha);
+    }
+    else // discard the pixel in texture rectangle which is transparent
+    {
         discard;
     }
 }