Add LCD support for distance field text

Add LCD support for distance field text.

LCD support is handled by shifting the uv coordinate by 1/3 of a pixel (transformed by the inverse CTM) to the left and right of the original texture coordinate, and using left, center, and right lookups to set the RGB values. This supports both RGB and BGR subpixel order. 

BUG=skia:2173
Committed: http://code.google.com/p/skia/source/detail?r=14049

[jvanverth1, 2014-04-03 15:26:59]

There isn't much of a performance loss with this despite the three texture
lookups, probably because the texture cache has already been loaded after the
first lookup.

[jvanverth1, 2014-04-03 15:44:19]

I've also added an additional comment about the single anti-aliasing factor,
since the length of the gradient might be slightly different when using
perspective matrices.

[robertphillips, 2014-04-03 15:48:02]

lgtm

[bungeman-skia, 2014-04-03 15:54:13]

Note that using lcd smoothing without gamma correction or a filter usually
doesn't look very good. What does this look like?

[bungeman-skia, 2014-04-03 16:07:18]

On 2014/04/03 15:54:13, bungeman1 wrote:
> Note that using lcd smoothing without gamma correction or a filter usually
> doesn't look very good. What does this look like?

Ah, now that I understand what's going on, you are doing a filter... ish thing.
So long as it looks good.

[jvanverth1, 2014-04-03 16:49:31]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2014-04-03 16:49:31]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/jvanverth@google.com/219243012/60001

[commit-bot: I haz the power, 2014-04-03 16:49:34]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-03 16:49:34]

Failed to apply patch for src/gpu/GrDistanceFieldTextContext.cpp:
While running patch -p1 --forward --force --no-backup-if-mismatch;
  patching file src/gpu/GrDistanceFieldTextContext.cpp
  Hunk #1 succeeded at 84 (offset 4 lines).
  Hunk #2 succeeded at 112 (offset 4 lines).
  Hunk #3 FAILED at 314.
  1 out of 3 hunks FAILED -- saving rejects to file
src/gpu/GrDistanceFieldTextContext.cpp.rej

Patch:       src/gpu/GrDistanceFieldTextContext.cpp
Index: src/gpu/GrDistanceFieldTextContext.cpp
diff --git a/src/gpu/GrDistanceFieldTextContext.cpp
b/src/gpu/GrDistanceFieldTextContext.cpp
index
638ec597074bbef9010c3faaea188000af41c4e1..d0834b1da5d5736fcdf704e227e17ed9869262ac
100755
--- a/src/gpu/GrDistanceFieldTextContext.cpp
+++ b/src/gpu/GrDistanceFieldTextContext.cpp
@@ -80,13 +80,18 @@ void GrDistanceFieldTextContext::flushGlyphs() {
         SkASSERT(fCurrTexture);
         GrTextureParams params(SkShader::kRepeat_TileMode,
GrTextureParams::kBilerp_FilterMode);
 
-        // This effect could be stored with one of the cache objects (atlas?)
-        drawState->addCoverageEffect(
-                         GrDistanceFieldTextureEffect::Create(fCurrTexture,
params,
-                                                             
fContext->getMatrix().isSimilarity()),
-                         kGlyphCoordsAttributeIndex)->unref();
+        // Effects could be stored with one of the cache objects (atlas?)
+        if (fUseLCDText) {
+            bool useBGR = SkDeviceProperties::Geometry::kBGR_Layout ==
+                                                           
fDeviceProperties.fGeometry.getLayout();
+           
drawState->addCoverageEffect(GrDistanceFieldLCDTextureEffect::Create(
+                                                            fCurrTexture,
+                                                            params,
+                                                           
fContext->getMatrix().rectStaysRect() &&
+                                                           
fContext->getMatrix().isSimilarity(),
+                                                            useBGR),
+                                         kGlyphCoordsAttributeIndex)->unref();
 
-        if (!GrPixelConfigIsAlphaOnly(fCurrTexture->config())) {
             if (kOne_GrBlendCoeff != fPaint.getSrcBlendCoeff() ||
                 kISA_GrBlendCoeff != fPaint.getDstBlendCoeff() ||
                 fPaint.numColorStages()) {
@@ -103,6 +108,10 @@ void GrDistanceFieldTextContext::flushGlyphs() {
            
drawState->setBlendConstant(skcolor_to_grcolor_nopremultiply(fSkPaint.getColor()));
             drawState->setBlendFunc(kConstC_GrBlendCoeff, kISC_GrBlendCoeff);
         } else {
+           
drawState->addCoverageEffect(GrDistanceFieldTextureEffect::Create(fCurrTexture,
params,
+                                                             
fContext->getMatrix().isSimilarity()),
+                                         kGlyphCoordsAttributeIndex)->unref();
+
             // set back to normal in case we took LCD path previously.
             drawState->setBlendFunc(fPaint.getSrcBlendCoeff(),
fPaint.getDstBlendCoeff());
             drawState->setColor(fPaint.getColor());
@@ -305,8 +314,10 @@ inline void GrDistanceFieldTextContext::init(const GrPaint&
paint, const SkPaint
 
     fTextRatio = fSkPaint.getTextSize()/kBaseDFFontSize;
 
-    fSkPaint.setTextSize(SkIntToScalar(kBaseDFFontSize));
+    fUseLCDText = fSkPaint.isLCDRenderText();
+    
     fSkPaint.setLCDRenderText(false);
+    fSkPaint.setTextSize(SkIntToScalar(kBaseDFFontSize));
     fSkPaint.setAutohinted(false);
     fSkPaint.setSubpixelText(true);
 }

[jvanverth1, 2014-04-03 17:08:02]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2014-04-03 17:08:11]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/jvanverth@google.com/219243012/80001

[commit-bot: I haz the power, 2014-04-03 18:26:03]

Change committed as 14049