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

src/gpu/GrBitmapTextContext.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrBitmapTextContext.h"
 #include "GrAtlas.h"
 #include "GrDrawTarget.h"
 #include "GrFontScaler.h"
 #include "GrIndexBuffer.h"
 #include "GrTextStrike.h"
 #include "GrTextStrike_impl.h"
+#include "SkColorPriv.h"
 #include "SkPath.h"
 #include "SkRTConf.h"
 #include "SkStrokeRec.h"
 #include "effects/GrCustomCoordsTextureEffect.h"
 
 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,
+                                         SkColor color) :
                                          GrTextContext(context, paint) {
     fAutoMatrix.setIdentity(fContext, &fPaint);
 
+    fSkPaintColor = color;
+
     fStrike = NULL;
 
     fCurrTexture = NULL;
     fCurrVertex = 0;
 
     fVertices = NULL;
     fMaxVertices = 0;
 }
 
 GrBitmapTextContext::~GrBitmapTextContext() {
     this->flushGlyphs();
 }
 
+static inline GrColor skcolor_to_grcolor_nopremultiply(SkColor c) {
+    unsigned r = SkColorGetR(c);
+    unsigned g = SkColorGetG(c);
+    unsigned b = SkColorGetB(c);
+    return GrColorPackRGBA(r, g, b, 0xff);
+}
+
 void GrBitmapTextContext::flushGlyphs() {
     if (NULL == fDrawTarget) {
         return;
     }
 
     GrDrawState* drawState = fDrawTarget->drawState();
     GrDrawState::AutoRestoreEffects are(drawState);
     drawState->setFromPaint(fPaint, SkMatrix::I(), fContext->getRenderTarget());
 
     if (fCurrVertex > 0) {
         // setup our sampler state for our text texture/atlas
         SkASSERT(GrIsALIGN4(fCurrVertex));
         SkASSERT(fCurrTexture);
         GrTextureParams params(SkShader::kRepeat_TileMode, GrTextureParams::kNone_FilterMode);
 
         // This effect could be stored with one of the cache objects (atlas?)
         drawState->addCoverageEffect(
                                 GrCustomCoordsTextureEffect::Create(fCurrTexture, params),
                                 kGlyphCoordsAttributeIndex)->unref();
 
         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 = SkColorGetA(fSkPaintColor);
+            // paintAlpha
+            drawState->setColor(SkColorSetARGB(a, a, a, a));
+            // paintColor
+            drawState->setBlendConstant(skcolor_to_grcolor_nopremultiply(fSkPaintColor));
             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);
         } else {
             // set back to normal in case we took LCD path previously.
             drawState->setBlendFunc(fPaint.getSrcBlendCoeff(), fPaint.getDstBlendCoeff());
             drawState->setColor(fPaint.getColor());
         }
 
         int nGlyphs = fCurrVertex / 4;
         fDrawTarget->setIndexSourceToBuffer(fContext->getQuadIndexBuffer());
         fDrawTarget->drawIndexedInstances(kTriangles_GrPrimitiveType,
                                           nGlyphs,
                                           4, 6);
+
         fDrawTarget->resetVertexSource();
         fVertices = NULL;
         fMaxVertices = 0;
         fCurrVertex = 0;
         SkSafeSetNull(fCurrTexture);
     }
 }
 
 namespace {
 
@@ skipping 144 matching lines @@
                                         SkFixedToFloat(vx + width),
                                         SkFixedToFloat(vy + height),
                                         2 * sizeof(SkPoint));
     fVertices[2*fCurrVertex+1].setRectFan(SkFixedToFloat(texture->normalizeFixedX(tx)),
                                           SkFixedToFloat(texture->normalizeFixedY(ty)),
                                           SkFixedToFloat(texture->normalizeFixedX(tx + width)),
                                           SkFixedToFloat(texture->normalizeFixedY(ty + height)),
                                           2 * sizeof(SkPoint));
     fCurrVertex += 4;
 }