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

The blend mode for LCD text was not set up correctly when using colors with alpha. This takes the color's alpha value
into account when setting up the blending function.

BUG=Skia:1728
R=bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/45363002

git-svn-id: http://skia.googlecode.com/svn/trunk@11980 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 22 insertions, 6 deletions

diff --git a/src/gpu/GrBitmapTextContext.cpp b/src/gpu/GrBitmapTextContext.cpp
index 7a99f093e5..737e24baa1 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,
+                                         SkColor color) :
                                          GrTextContext(context, paint) {
     fAutoMatrix.setIdentity(fContext, &fPaint);
 
+    fSkPaintColor = color;
+
     fStrike = NULL;
 
     fCurrTexture = NULL;
@@ -39,6 +43,13 @@ 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;
@@ -65,12 +76,16 @@ void GrBitmapTextContext::flushGlyphs() {
                 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());
@@ -82,6 +97,7 @@ void GrBitmapTextContext::flushGlyphs() {
         fDrawTarget->drawIndexedInstances(kTriangles_GrPrimitiveType,
                                           nGlyphs,
                                           4, 6);
+
         fDrawTarget->resetVertexSource();
         fVertices = NULL;
         fMaxVertices = 0;