AlphaShader for mapping alpha in pre-render

ImageShader.cpp

@@ -8,7 +8,7 @@
 #include "ImageShader.h"
 
 ShadingProgram imageShadingProgram("shaders/image.vs", "shaders/image.fs");
-ShadingProgram inverseAlphaProgram("shaders/image.vs", "shaders/imageblending.fs");
+ShadingProgram imageAlphaProgram  ("shaders/image.vs", "shaders/imageblending.fs");
 
 const char* MaskShader::mask_names[3]  = { ICON_FA_EXPAND, ICON_FA_EDIT, ICON_FA_SHAPES };
 const char* MaskShader::mask_shapes[5] = { "Elipse", "Oblong", "Rectangle", "Horizontal", "Vertical" };
@@ -62,10 +62,10 @@ void ImageShader::accept(Visitor& v) {
 }
 
 
-DivideAlphaShader::DivideAlphaShader(): ImageShader()
+AlphaShader::AlphaShader(): ImageShader()
 {
     // to inverse alpha mode, use dedicated shading program
-    program_ = &inverseAlphaProgram;
+    program_ = &imageAlphaProgram;
     // reset instance
     reset();
 

ImageShader.h

@@ -27,11 +27,11 @@ public:
     float stipple;
 };
 
-class DivideAlphaShader : public ImageShader
+class AlphaShader : public ImageShader
 {
 
 public:
-    DivideAlphaShader();
+    AlphaShader();
 
 };
 

rsc/shaders/imageblending.fs

@@ -22,15 +22,7 @@ void main()
 
     // color texture
     vec4 textureColor = texture(iChannel0, texcoord.xy);
-    vec3 RGB = textureColor.rgb * vertexColor.rgb * color.rgb;
-
-    // alpha is a mix of texture, vertex, uniform and mask alpha
-    float A = textureColor.a * vertexColor.a * color.a;
-
-    // post-reversing premultiplication of alpha
-    float invA = 1.0 / clamp( A , 0.000001, 10.0);
-//    float invA = 1.0 / (A*A);
 
     // output
-    FragColor = vec4( RGB * invA, A);
+    FragColor = vec4( textureColor.a);
 }