refine fastShadow (to best match non-fastShadow effects)

Author: zhuxingwei

Runtime/Resources/shaders/UIWidgets_canvas_shadowBox.shader

@@ -3,15 +3,13 @@ Shader "UIWidgets/ShadowBox"
     //originally from http://madebyevan.com/shaders/fast-rounded-rectangle-shadows/
     Properties
     {
-        _SrcBlend("_SrcBlend", Int) = 1 // One
-        _DstBlend("_DstBlend", Int) = 10 // OneMinusSrcAlpha
         _StencilComp("_StencilComp", Float) = 8 // - Equal, 8 - Always 
     }
     SubShader
     {
         ZTest Always
         ZWrite Off
-        Blend [_SrcBlend] [_DstBlend]
+        Blend SrcAlpha OneMinusSrcAlpha
 
         Stencil {
             Ref 128

Runtime/Resources/shaders/UIWidgets_canvas_shadowRBox.shader

@@ -3,15 +3,13 @@ Shader "UIWidgets/ShadowRBox"
     //originally from http://madebyevan.com/shaders/fast-rounded-rectangle-shadows/
     Properties
     {
-        _SrcBlend("_SrcBlend", Int) = 1 // One
-        _DstBlend("_DstBlend", Int) = 10 // OneMinusSrcAlpha
         _StencilComp("_StencilComp", Float) = 8 // - Equal, 8 - Always 
     }
     SubShader
     {
         ZTest Always
         ZWrite Off
-        Blend [_SrcBlend] [_DstBlend]
+        Blend SrcAlpha OneMinusSrcAlpha
 
         Stencil {
             Ref 128

Runtime/Resources/shaders/computebuffer/UIWidgets_canvas_shadowBox_cb.shader

@@ -3,15 +3,13 @@ Shader "UIWidgets/ShadowBox_cb"
     //originally from http://madebyevan.com/shaders/fast-rounded-rectangle-shadows/
     Properties
     {
-        _SrcBlend("_SrcBlend", Int) = 1 // One
-        _DstBlend("_DstBlend", Int) = 10 // OneMinusSrcAlpha
         _StencilComp("_StencilComp", Float) = 8 // - Equal, 8 - Always 
     }
     SubShader
     {
         ZTest Always
         ZWrite Off
-        Blend [_SrcBlend] [_DstBlend]
+        Blend SrcAlpha OneMinusSrcAlpha
 
         Stencil {
             Ref 128

Runtime/Resources/shaders/computebuffer/UIWidgets_canvas_shadowRBox_cb.shader

@@ -3,15 +3,13 @@ Shader "UIWidgets/ShadowRBox_cb"
     //originally from http://madebyevan.com/shaders/fast-rounded-rectangle-shadows/
     Properties
     {
-        _SrcBlend("_SrcBlend", Int) = 1 // One
-        _DstBlend("_DstBlend", Int) = 10 // OneMinusSrcAlpha
         _StencilComp("_StencilComp", Float) = 8 // - Equal, 8 - Always 
     }
     SubShader
     {
         ZTest Always
         ZWrite Off
-        Blend [_SrcBlend] [_DstBlend]
+        Blend SrcAlpha OneMinusSrcAlpha
 
         Stencil {
             Ref 128

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

@@ -46,7 +46,7 @@ void _drawRRectShadow(uiPath path, uiPaint paint) {
             }
 
             var bound =  path.getBounds();
-            var sigma = state.scale * paint.maskFilter.Value.sigma;
+            var sigma = state.scale * paint.maskFilter.Value.sigma / 3f;
 
             var vertices = ObjectPool<uiList<Vector3>>.alloc();
             vertices.SetCapacity(4);
@@ -67,7 +67,8 @@ void _drawRRectShadow(uiPath path, uiPaint paint) {
             ObjectPool<uiMeshMesh>.release(meshBounds);
             ObjectPool<uiMeshMesh>.release(blurMesh);
             var mesh = uiMeshMesh.create(state.matrix, vertices, _triangles);
-            layer.draws.Add(CanvasShader.fastShadow(layer, mesh, sigma, path.isRect, path.isCircle, path.rRectCorner, new Vector4(bound.left, bound.top, bound.right, bound.bottom), paint.color));
+            var shadowColor = paint.color.withAlpha(128);
+            layer.draws.Add(CanvasShader.fastShadow(layer, mesh, sigma, path.isRect, path.isCircle, path.rRectCorner, new Vector4(bound.left, bound.top, bound.right, bound.bottom), shadowColor));
         }
 
     }