Fix issue in stroke alpha shader.

Author: Yuncong Zhang

Runtime/Resources/UIWidgets_canvas.cginc

@@ -184,5 +184,5 @@ float strokeMask(float u, float v) {
 }
 
 fixed4 frag_stroke_alpha(v2f i) : SV_Target {
-    return _color * strokeMask(i.ftcoord.x, i.ftcoord.y);
+    return shader_color(i) * strokeMask(i.ftcoord.x, i.ftcoord.y);
 }

Runtime/Resources/UIWidgets_canvas_strokeAlpha.shader

@@ -25,5 +25,41 @@ Shader "UIWidgets/canvas_strokeAlpha"
             #pragma fragment frag_stroke_alpha
             ENDCG
         }
+        
+        Pass { // 1, linear
+            CGPROGRAM
+            #define UIWIDGETS_LINEAR
+            #include "UIWidgets_canvas.cginc"
+            #pragma vertex vert
+            #pragma fragment frag_stroke_alpha
+            ENDCG
+        }
+
+        Pass { // 2, radial
+            CGPROGRAM
+            #define UIWIDGETS_RADIAL
+            #include "UIWidgets_canvas.cginc"
+            #pragma vertex vert
+            #pragma fragment frag_stroke_alpha
+            ENDCG
+        }
+
+        Pass { // 3, sweep
+            CGPROGRAM
+            #define UIWIDGETS_SWEEP
+            #include "UIWidgets_canvas.cginc"
+            #pragma vertex vert
+            #pragma fragment frag_stroke_alpha
+            ENDCG
+        }
+        
+        Pass { // 4, image
+            CGPROGRAM
+            #define UIWIDGETS_IMAGE
+            #include "UIWidgets_canvas.cginc"
+            #pragma vertex vert
+            #pragma fragment frag_stroke_alpha
+            ENDCG
+        }
     }
 }

Runtime/ui/renderer/cmdbufferCanvas/rendering/canvas_shader.cs

@@ -392,7 +392,7 @@ public static PictureFlusher.CmdDraw strokeAlpha(PictureFlusher.RenderLayer laye
 
             return PictureFlusher.CmdDraw.create(
                 mesh: mesh,
-                pass: 0,
+                pass: pass,
                 material: mat,
                 properties: props
             );