Emulate gamma fix by making glyphs thicker or thinner

src/gpu/GrDistanceFieldTextContext.cpp

Index: src/gpu/GrDistanceFieldTextContext.cpp
diff --git a/src/gpu/GrDistanceFieldTextContext.cpp b/src/gpu/GrDistanceFieldTextContext.cpp
index acab0cf7681cfcc094144e34802262c451396bd0..f2660d33f439b16953a0d38c24da9f0ddd1b9662 100755
--- a/src/gpu/GrDistanceFieldTextContext.cpp
+++ b/src/gpu/GrDistanceFieldTextContext.cpp
@@ -42,6 +42,11 @@ static const int kLargeDFFontSize = 162;
 static const int kVerticesPerGlyph = 4;
 static const int kIndicesPerGlyph = 6;
 
+#ifdef SK_DEBUG
+static const int kExpectedWidthAdjustTableSize = 8;
+#endif
+static const int kWidthAdjustLumShift = 5;
+
 GrDistanceFieldTextContext::GrDistanceFieldTextContext(GrContext* context,
                                                        SkGpuDevice* gpuDevice,
                                                        const SkDeviceProperties& properties,
@@ -53,7 +58,7 @@ GrDistanceFieldTextContext::GrDistanceFieldTextContext(GrContext* context,
     fEnableDFRendering = enable;
 #endif
     fStrike = NULL;
-    fGammaTexture = NULL;
+    fWidthAdjustTable = NULL;
 
     fEffectTextureUniqueID = SK_InvalidUniqueID;
     fEffectColor = GrColor_ILLEGAL;
@@ -74,6 +79,7 @@ GrDistanceFieldTextContext* GrDistanceFieldTextContext::Create(GrContext* contex
                                                                bool enable) {
     GrDistanceFieldTextContext* textContext = SkNEW_ARGS(GrDistanceFieldTextContext, 
                                                          (context, gpuDevice, props, enable));
+    textContext->buildWidthAdjustTable();
 #ifdef USE_BITMAP_TEXTBLOBS
     textContext->fFallbackTextContext = GrBitmapTextContextB::Create(context, gpuDevice, props);
 #else
@@ -83,8 +89,56 @@ GrDistanceFieldTextContext* GrDistanceFieldTextContext::Create(GrContext* contex
     return textContext;
 }
 
+
+void GrDistanceFieldTextContext::buildWidthAdjustTable() {
+    int width, height;
+    size_t size;
+
+#ifdef SK_GAMMA_CONTRAST
+    SkScalar contrast = SK_GAMMA_CONTRAST;
+#else
+    SkScalar contrast = 0.5f;
+#endif
+    SkScalar paintGamma = fDeviceProperties.gamma();
+    SkScalar deviceGamma = fDeviceProperties.gamma();
+
+    size = SkScalerContext::GetGammaLUTSize(contrast, paintGamma, deviceGamma,
+        &width, &height);
+   
+    SkASSERT(kExpectedWidthAdjustTableSize == height);
+    fWidthAdjustTable = SkNEW_ARRAY(SkScalar, height);
+
+    SkAutoTArray<uint8_t> data((int)size);
+    SkScalerContext::GetGammaLUTData(contrast, paintGamma, deviceGamma, data.get());
+
+    // find the inverse points where we cross 0.5
+    // binsearch might be better, but we only need to do this once on creation
+    for (int row = 0; row < height; ++row) {
+        uint8_t* rowPtr = data.get() + row*width;
+        for (int col = 0; col < width - 1; ++col) {
+            if (rowPtr[col] <= 127 && rowPtr[col + 1] >= 128) {
+                // compute point where a mask value will give us a result of 0.5
+                float interp = (127.5f - rowPtr[col]) / (rowPtr[col + 1] - rowPtr[col]);
+                float borderAlpha = (col + interp) / 255.f;
+
+                // compute t value for that alpha
+                // this is an approximate inverse for smoothstep()
+                float t = borderAlpha*(borderAlpha*(4.0f*borderAlpha - 6.0f) + 5.0f) / 3.0f;
+
+                // compute distance which gives us that t value
+                float d = 2.0f*0.7071f*t - 0.7071f;
+
+                fWidthAdjustTable[row] = d;
+                break;
+            }
+        }
+    }
+}
+
+
 GrDistanceFieldTextContext::~GrDistanceFieldTextContext() {
-    SkSafeSetNull(fGammaTexture);
+    SkDELETE_ARRAY(fWidthAdjustTable);
+    fWidthAdjustTable = NULL;
 }
 
 bool GrDistanceFieldTextContext::canDraw(const GrRenderTarget* rt,
@@ -182,45 +236,6 @@ inline void GrDistanceFieldTextContext::init(GrRenderTarget* rt, const GrClip& c
     fSkPaint.setSubpixelText(true);
 }
 
-static void setup_gamma_texture(GrContext* context, const SkGlyphCache* cache,
-                                const SkDeviceProperties& deviceProperties,
-                                GrTexture** gammaTexture) {
-    if (NULL == *gammaTexture) {
-        int width, height;
-        size_t size;
-
-#ifdef SK_GAMMA_CONTRAST
-        SkScalar contrast = SK_GAMMA_CONTRAST;
-#else
-        SkScalar contrast = 0.5f;
-#endif
-        SkScalar paintGamma = deviceProperties.gamma();
-        SkScalar deviceGamma = deviceProperties.gamma();
-
-        size = SkScalerContext::GetGammaLUTSize(contrast, paintGamma, deviceGamma,
-                                                &width, &height);
-
-        SkAutoTArray<uint8_t> data((int)size);
-        SkScalerContext::GetGammaLUTData(contrast, paintGamma, deviceGamma, data.get());
-
-        // TODO: Update this to use the cache rather than directly creating a texture.
-        GrSurfaceDesc desc;
-        desc.fFlags = kNone_GrSurfaceFlags;
-        desc.fWidth = width;
-        desc.fHeight = height;
-        desc.fConfig = kAlpha_8_GrPixelConfig;
-
-        *gammaTexture = context->getGpu()->createTexture(desc, true, NULL, 0);
-        if (NULL == *gammaTexture) {
-            return;
-        }
-
-        (*gammaTexture)->writePixels(0, 0, width, height,
-                                     (*gammaTexture)->config(), data.get(), 0,
-                                     GrContext::kDontFlush_PixelOpsFlag);
-    }
-}
-
 void GrDistanceFieldTextContext::onDrawText(GrRenderTarget* rt, const GrClip& clip,
                                             const GrPaint& paint,
                                             const SkPaint& skPaint, const SkMatrix& viewMatrix,
@@ -313,8 +328,6 @@ void GrDistanceFieldTextContext::onDrawPosText(GrRenderTarget* rt, const GrClip&
     SkGlyphCache*              cache = autoCache.getCache();
     GrFontScaler*              fontScaler = GetGrFontScaler(cache);
 
-    setup_gamma_texture(fContext, cache, fDeviceProperties, &fGammaTexture);
-
     int numGlyphs = fSkPaint.textToGlyphs(text, byteLength, NULL);
     fTotalVertexCount = kVerticesPerGlyph*numGlyphs;
 
@@ -442,13 +455,22 @@ void GrDistanceFieldTextContext::setupCoverageEffect(const SkColor& filteredColo
         GrColor color = fPaint.getColor();
         if (fUseLCDText) {
             GrColor colorNoPreMul = skcolor_to_grcolor_nopremultiply(filteredColor);
+
+            float redCorrection = 
+                fWidthAdjustTable[GrColorUnpackR(colorNoPreMul) >> kWidthAdjustLumShift];
+            float greenCorrection = 
+                fWidthAdjustTable[GrColorUnpackG(colorNoPreMul) >> kWidthAdjustLumShift];
+            float blueCorrection = 
+                fWidthAdjustTable[GrColorUnpackB(colorNoPreMul) >> kWidthAdjustLumShift];
+            GrDistanceFieldLCDTextureEffect::WidthAdjust widthAdjust =
+                GrDistanceFieldLCDTextureEffect::WidthAdjust::Make(redCorrection,
+                                                                   greenCorrection,
+                                                                   blueCorrection);
             fCachedGeometryProcessor.reset(GrDistanceFieldLCDTextureEffect::Create(color,
                                                                                    fViewMatrix,
                                                                                    fCurrTexture,
                                                                                    params,
-                                                                                   fGammaTexture,
-                                                                                   gammaParams,
-                                                                                   colorNoPreMul,
+                                                                                   widthAdjust,
                                                                                    flags));
         } else {
             flags |= kColorAttr_DistanceFieldEffectFlag;
@@ -456,13 +478,12 @@ void GrDistanceFieldTextContext::setupCoverageEffect(const SkColor& filteredColo
 #ifdef SK_GAMMA_APPLY_TO_A8
             U8CPU lum = SkColorSpaceLuminance::computeLuminance(fDeviceProperties.gamma(),
                                                                 filteredColor);
+            float correction = fWidthAdjustTable[lum >> kWidthAdjustLumShift];
             fCachedGeometryProcessor.reset(GrDistanceFieldTextureEffect::Create(color,
                                                                                 fViewMatrix,
                                                                                 fCurrTexture,
                                                                                 params,
-                                                                                fGammaTexture,
-                                                                                gammaParams,
-                                                                                lum/255.f,
+                                                                                correction,
                                                                                 flags,
                                                                                 opaque));
 #else