Resubmit support for subpixel antialiasing on text in the GL2 engine.

The antialiasing is currently not gamma corrected and is disabled on
OpenGL ES 2.0.

Reviewed-by: Samuel

1 files changed, 33 insertions, 0 deletions

diff --git a/src/opengl/gl2paintengineex/qglengineshadersource_p.h b/src/opengl/gl2paintengineex/qglengineshadersource_p.h
index 6bcf010..8ae86d3 100644
--- a/src/opengl/gl2paintengineex/qglengineshadersource_p.h
+++ b/src/opengl/gl2paintengineex/qglengineshadersource_p.h
@@ -401,6 +401,39 @@ static const char* const qglslMaskFragmentShader = "\
         return src * mask.a; \
     }";
 
+// For source over with subpixel antialiasing, the final color is calculated per component as follows
+// (.a is alpha component, .c is red, green or blue component):
+// alpha = src.a * mask.c * opacity
+// dest.c = dest.c * (1 - alpha) + src.c * alpha
+//
+// In the first pass, calculate: dest.c = dest.c * (1 - alpha) with blend funcs: zero, 1 - source color
+// In the second pass, calculate: dest.c = dest.c + src.c * alpha with blend funcs: one, one
+//
+// If source is a solid color (src is constant), only the first pass is needed, with blend funcs: constant, 1 - source color
+
+// For source composition with subpixel antialiasing, the final color is calculated per component as follows:
+// alpha = src.a * mask.c * opacity
+// dest.c = dest.c * (1 - mask.c) + src.c * alpha
+//
+
+static const char* const qglslRgbMaskFragmentShaderPass1 = "\
+    varying highp   vec2      textureCoords;\
+    uniform lowp    sampler2D maskTexture;\
+    lowp vec4 applyMask(lowp vec4 src) \
+    {\
+        lowp vec4 mask = texture2D(maskTexture, textureCoords); \
+        return src.a * mask; \
+    }";
+
+static const char* const qglslRgbMaskFragmentShaderPass2 = "\
+    varying highp   vec2      textureCoords;\
+    uniform lowp    sampler2D maskTexture;\
+    lowp vec4 applyMask(lowp vec4 src) \
+    {\
+        lowp vec4 mask = texture2D(maskTexture, textureCoords); \
+        return src * mask; \
+    }";
+
 /*
     Left to implement:
         RgbMaskFragmentShader,