Fix for issue 1728: raster vs. gpu text draws with the wrong color

src/gpu/GrBitmapTextContext.cpp

Index: src/gpu/GrBitmapTextContext.cpp
diff --git a/src/gpu/GrBitmapTextContext.cpp b/src/gpu/GrBitmapTextContext.cpp
index 7a99f093e5149108163a402a2aa9ee7788dc1f47..aebc53794d81606683529eebc447b7163f46881c 100755
--- a/src/gpu/GrBitmapTextContext.cpp
+++ b/src/gpu/GrBitmapTextContext.cpp
@@ -12,6 +12,7 @@
 #include "GrIndexBuffer.h"
 #include "GrTextStrike.h"
 #include "GrTextStrike_impl.h"
+#include "SkColorPriv.h"
 #include "SkPath.h"
 #include "SkRTConf.h"
 #include "SkStrokeRec.h"
@@ -22,10 +23,13 @@ static const int kGlyphCoordsAttributeIndex = 1;
 SK_CONF_DECLARE(bool, c_DumpFontCache, "gpu.dumpFontCache", false,
                 "Dump the contents of the font cache before every purge.");
 
-GrBitmapTextContext::GrBitmapTextContext(GrContext* context, const GrPaint& paint) :
+GrBitmapTextContext::GrBitmapTextContext(GrContext* context, const GrPaint& paint,
+                                         GrColor color) :
                                          GrTextContext(context, paint) {
     fAutoMatrix.setIdentity(fContext, &fPaint);
 
+    fPaintColorNoPreMultAlpha = color;
+
     fStrike = NULL;
 
     fCurrTexture = NULL;
@@ -59,18 +63,21 @@ void GrBitmapTextContext::flushGlyphs() {
                                 GrCustomCoordsTextureEffect::Create(fCurrTexture, params),
                                 kGlyphCoordsAttributeIndex)->unref();
 
+        bool lcdAlpha = false;

[bsalomon, 2013/10/28 13:12:21]

this and the below code guarded by this var don't appear to be used anymore.

[jvanverth1, 2013/10/28 14:00:52]

Done.

         if (!GrPixelConfigIsAlphaOnly(fCurrTexture->config())) {
             if (kOne_GrBlendCoeff != fPaint.getSrcBlendCoeff() ||
                 kISA_GrBlendCoeff != fPaint.getDstBlendCoeff() ||
                 fPaint.numColorStages()) {
                 GrPrintf("LCD Text will not draw correctly.\n");
             }
-            // setup blend so that we get mask * paintColor + (1-mask)*dstColor
-            drawState->setBlendConstant(fPaint.getColor());
+            // We don't use the GrPaint's color in this case because it's been premultiplied by
+            // alpha. Instead we feed in a non-premultiplied color, and multiply its alpha by
+            // the mask texture color. The end result is that we get 
+            //            mask*paintAlpha*paintColor + (1-mask*paintAlpha)*dstColor
+            int a = SkGetPackedA32(fPaintColorNoPreMultAlpha);
+            drawState->setBlendConstant(fPaintColorNoPreMultAlpha);
             drawState->setBlendFunc(kConstC_GrBlendCoeff, kISC_GrBlendCoeff);
-            // don't modulate by the paint's color in the frag since we're
-            // already doing it via the blend const.
-            drawState->setColor(0xffffffff);
+            drawState->setColor(SkColorSetARGB(a, a, a, a));
         } else {
             // set back to normal in case we took LCD path previously.
             drawState->setBlendFunc(fPaint.getSrcBlendCoeff(), fPaint.getDstBlendCoeff());
@@ -82,6 +89,16 @@ void GrBitmapTextContext::flushGlyphs() {
         fDrawTarget->drawIndexedInstances(kTriangles_GrPrimitiveType,
                                           nGlyphs,
                                           4, 6);
+
+        if (lcdAlpha) {
+            // in second pass add mask*paintColor to dst
+            drawState->setBlendFunc(kOne_GrBlendCoeff, kOne_GrBlendCoeff);
+            drawState->setColor(fPaint.getColor());
+            fDrawTarget->drawIndexedInstances(kTriangles_GrPrimitiveType,
+                                          nGlyphs,
+                                          4, 6);
+        }
+
         fDrawTarget->resetVertexSource();
         fVertices = NULL;
         fMaxVertices = 0;