From 27112a2b573fa9f836e036aed888de77a7db4f56 Mon Sep 17 00:00:00 2001
From: brunoherbelin <bruno.herbelin@gmail.com>
Date: Mon, 22 Feb 2021 18:26:00 +0100
Subject: [PATCH] AlphaShader for mapping alpha in pre-render

---
 ImageShader.cpp              |  6 +++---
 ImageShader.h                |  4 ++--
 rsc/shaders/imageblending.fs | 10 +---------
 3 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/ImageShader.cpp b/ImageShader.cpp
index 5d140ea..0e4bd33 100644
--- a/ImageShader.cpp
+++ b/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();
 
diff --git a/ImageShader.h b/ImageShader.h
index f2d3f7c..8d0c89d 100644
--- a/ImageShader.h
+++ b/ImageShader.h
@@ -27,11 +27,11 @@ public:
     float stipple;
 };
 
-class DivideAlphaShader : public ImageShader
+class AlphaShader : public ImageShader
 {
 
 public:
-    DivideAlphaShader();
+    AlphaShader();
 
 };
 
diff --git a/rsc/shaders/imageblending.fs b/rsc/shaders/imageblending.fs
index c5534d2..6116b7b 100644
--- a/rsc/shaders/imageblending.fs
+++ b/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);
 }