when drawing a transformed bitmap in opengl backend, scale it better

The plain scaling is rather rough, and in fact drawing a scaled bitmap
the normal way gives much better results (because OutputDevice pre-scales
the bitmap before it's drawn). This one may be a bit slow perhaps,
but hopefully nobody there's no code that'd extensively use bitmap
drawing with custom transformations (wishful thinking).

Change-Id: I83e05307adfaeac0ed0757f1a0b2603f64caf8f8

1 files changed, 13 insertions, 0 deletions

diff --git a/vcl/opengl/areaScaleFragmentShader.glsl b/vcl/opengl/areaScaleFragmentShader.glsl
index 498b0b53ec4b..d72184cc2911 100644
--- a/vcl/opengl/areaScaleFragmentShader.glsl
+++ b/vcl/opengl/areaScaleFragmentShader.glsl
@@ -27,6 +27,12 @@ uniform float ydestconvert;
 
 varying vec2 tex_coord;
 
+// This mode makes the scaling work like maskedTextureFragmentShader.glsl
+// (instead of like plain textureVertexShader.glsl).
+#ifdef MASKED
+uniform sampler2D mask;
+#endif
+
 void main(void)
 {
     // Convert to pixel coordinates again.
@@ -126,7 +132,14 @@ void main(void)
         for( int x = xstart; x <= xend; ++x, ++xpos )
         {
             vec2 offset = vec2( x * xsrcconvert, y * ysrcconvert );
+#ifndef MASKED
             tmp += texture2D( sampler, offset ) * xratio[ xpos ];
+#else
+            vec4 texel;
+            texel = texture2D( sampler, offset );
+            texel.a = 1.0 - texture2D( mask, offset ).r;
+            tmp += texel * xratio[ xpos ];
+#endif
         }
         sum += tmp * yratio[ ypos ];
     }