Correct sub-pixel font rendering with OpenGL

Uses the GL_ARB_blend_func_extended to get single-pass, per-channel
alpha blending. gl_generator is now used instead of gl to enable the
extension.

The background color is removed since that presumably needs to run in a
separate pass.

1 files changed, 5 insertions, 21 deletions

diff --git a/res/text.f.glsl b/res/text.f.glsl
index 7e80a11c..3389fd7e 100644
--- a/res/text.f.glsl
+++ b/res/text.f.glsl
@@ -1,30 +1,14 @@
 #version 330 core
 in vec2 TexCoords;
 
+layout(location = 0, index = 0) out vec4 color;
+layout(location = 0, index = 1) out vec4 alphaMask;
+
 uniform sampler2D mask;
 uniform vec3 textColor;
-uniform vec3 bgColor;
-
-// SRC = SRC_ALPHA; DST = 1 - SRC_ALPHA
-void MyBlend(in vec3 srcValue,
-             in vec3 dstValue,
-             in vec3 srcAlpha,
-             out vec3 blended)
-{
-    vec3 dstAlpha = vec3(1.0, 1.0, 1.0) - srcAlpha;
-    vec3 preBlended = (srcValue * srcAlpha + dstValue * dstAlpha);
-
-    blended = vec3(min(1.0, preBlended.x),
-                   min(1.0, preBlended.y),
-                   min(1.0, preBlended.z));
-}
 
 void main()
 {
-    // vec4 red = vec4(sampled.rgb, sampled.r * sampled.g * sampled.b);
-    // vec4 sampled = vec4(1.0, 1.0, 1.0, texture(mask, TexCoords));
-    vec3 blended = vec3(1.0, 1.0, 1.0);
-    MyBlend(textColor, bgColor, texture(mask, TexCoords).rgb, blended);
-
-    gl_FragColor = vec4(blended, 1.0);
+    alphaMask = vec4(texture(mask, TexCoords).rgb, 1.);
+    color = vec4(textColor, 1.);
 }