Gamma correction for distance field text.

src/gpu/GrDistanceFieldTextContext.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 "GrDistanceFieldTextContext.h"
 #include "GrAtlas.h"
+#include "SkColorFilter.h"
 #include "GrDrawTarget.h"
 #include "GrDrawTargetCaps.h"
 #include "GrFontScaler.h"
 #include "SkGlyphCache.h"
+#include "GrGpu.h"
 #include "GrIndexBuffer.h"
 #include "GrTextStrike.h"
 #include "GrTextStrike_impl.h"
 #include "SkDistanceFieldGen.h"
 #include "SkDraw.h"
 #include "SkGpuDevice.h"
 #include "SkPath.h"
 #include "SkRTConf.h"
 #include "SkStrokeRec.h"
 #include "effects/GrDistanceFieldTextureEffect.h"
@@ skipping 12 matching lines @@
 GrDistanceFieldTextContext::GrDistanceFieldTextContext(GrContext* context,
                                                        const SkDeviceProperties& properties,
                                                        bool enable)
                                                     : GrTextContext(context, properties) {
 #if SK_FORCE_DISTANCEFIELD_FONTS
     fEnableDFRendering = true;
 #else
     fEnableDFRendering = enable;
 #endif
     fStrike = NULL;
+    fGammaTexture = NULL;
 
     fCurrTexture = NULL;
     fCurrVertex = 0;
 
     fVertices = NULL;
     fMaxVertices = 0;
 }
 
 GrDistanceFieldTextContext::~GrDistanceFieldTextContext() {
     this->flushGlyphs();
+    SkSafeSetNull(fGammaTexture);
 }
 
 bool GrDistanceFieldTextContext::canDraw(const SkPaint& paint) {
     if (!fEnableDFRendering && !paint.isDistanceFieldTextTEMP()) {
         return false;
     }
 
     // rasterizers and mask filters modify alpha, which doesn't
     // translate well to distance
     if (paint.getRasterizer() || paint.getMaskFilter() ||
@@ skipping 34 matching lines @@
     GrDrawState::AutoRestoreEffects are(drawState);
     drawState->setFromPaint(fPaint, fContext->getMatrix(), fContext->getRenderTarget());
 
     if (fCurrVertex > 0) {
         fContext->getFontCache()->updateTextures();
 
         // setup our sampler state for our text texture/atlas
         SkASSERT(SkIsAlign4(fCurrVertex));
         SkASSERT(fCurrTexture);
         GrTextureParams params(SkShader::kRepeat_TileMode, GrTextureParams::kBilerp_FilterMode);
+        GrTextureParams gammaParams(SkShader::kClamp_TileMode, GrTextureParams::kNone_FilterMode);
 
         // Effects could be stored with one of the cache objects (atlas?)
+        SkColor filteredColor;
+        SkColorFilter* colorFilter = fSkPaint.getColorFilter();
+        if (NULL != colorFilter) {
+            filteredColor = colorFilter->filterColor(fSkPaint.getColor());
+        } else {
+            filteredColor = fSkPaint.getColor();
+        }
         if (fUseLCDText) {
+            GrColor colorNoPreMul = skcolor_to_grcolor_nopremultiply(filteredColor);
             bool useBGR = SkDeviceProperties::Geometry::kBGR_Layout ==
                                                             fDeviceProperties.fGeometry.getLayout();
             drawState->addCoverageEffect(GrDistanceFieldLCDTextureEffect::Create(
                                                             fCurrTexture,
                                                             params,
+                                                            fGammaTexture,
+                                                            gammaParams,
+                                                            colorNoPreMul,
                                                             fContext->getMatrix().rectStaysRect() &&
                                                             fContext->getMatrix().isSimilarity(),
                                                             useBGR),
                                          kGlyphCoordsAttributeIndex)->unref();
 
             if (kOne_GrBlendCoeff != fPaint.getSrcBlendCoeff() ||
                 kISA_GrBlendCoeff != fPaint.getDstBlendCoeff() ||
                 fPaint.numColorStages()) {
                 GrPrintf("LCD Text will not draw correctly.\n");
             }
             // 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(fSkPaint.getColor());
             // paintAlpha
             drawState->setColor(SkColorSetARGB(a, a, a, a));
             // paintColor
-            drawState->setBlendConstant(skcolor_to_grcolor_nopremultiply(fSkPaint.getColor()));
+            drawState->setBlendConstant(colorNoPreMul);
             drawState->setBlendFunc(kConstC_GrBlendCoeff, kISC_GrBlendCoeff);
         } else {
-            drawState->addCoverageEffect(GrDistanceFieldTextureEffect::Create(fCurrTexture, params,
+#ifdef SK_GAMMA_APPLY_TO_A8
+            U8CPU lum = SkColorSpaceLuminance::computeLuminance(fDeviceProperties.fGamma,
+                                                                filteredColor);
+            drawState->addCoverageEffect(GrDistanceFieldTextureEffect::Create(
+                                                              fCurrTexture, params,
+                                                              fGammaTexture, gammaParams,
+                                                              lum/255.f,
                                                               fContext->getMatrix().isSimilarity()),
                                          kGlyphCoordsAttributeIndex)->unref();
-
+#else
+            drawState->addCoverageEffect(GrDistanceFieldTextureEffect::Create(
+                                                              fCurrTexture, params,
+                                                              fContext->getMatrix().isSimilarity()),
+                                         kGlyphCoordsAttributeIndex)->unref();
+#endif
             // 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);
@@ skipping 194 matching lines @@
     } else if (fSkPaint.getTextSize() <= kMediumDFFontLimit) {
         fTextRatio = fSkPaint.getTextSize()/kMediumDFFontSize;
         fSkPaint.setTextSize(SkIntToScalar(kMediumDFFontSize));
     } else {
         fTextRatio = fSkPaint.getTextSize()/kLargeDFFontSize;
         fSkPaint.setTextSize(SkIntToScalar(kLargeDFFontSize));
     }
 
     fUseLCDText = fSkPaint.isLCDRenderText();
 
-    fSkPaint.setLCDRenderText(false);
-    fSkPaint.setAutohinted(false);
-    fSkPaint.setSubpixelText(true);
+    fSkPaint.setDistanceFieldTextTEMP(true);
 }
 
 inline void GrDistanceFieldTextContext::finish() {
     flushGlyphs();
 
     GrTextContext::finish();
 }
 
+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.fGamma;
+        SkScalar deviceGamma = deviceProperties.fGamma;
+
+        size = cache->getScalerContext()->getGammaLUTSize(contrast, paintGamma, deviceGamma,
+                                                          &width, &height);
+
+        SkAutoTArray<uint8_t> data((int)size);
+        cache->getScalerContext()->getGammaLUTData(contrast, paintGamma, deviceGamma, data.get());
+
+        // TODO: Update this to use the cache rather than directly creating a texture.
+        GrTextureDesc desc;
+        desc.fFlags = kDynamicUpdate_GrTextureFlagBit;
+        desc.fWidth = width;
+        desc.fHeight = height;
+        desc.fConfig = kAlpha_8_GrPixelConfig;
+
+        *gammaTexture = context->getGpu()->createTexture(desc, NULL, 0);
+        if (NULL == *gammaTexture) {
+            return;
+        }
+
+        context->writeTexturePixels(*gammaTexture,
+                                    0, 0, width, height,
+                                    (*gammaTexture)->config(), data.get(), 0,
+                                    GrContext::kDontFlush_PixelOpsFlag);
+    }
+}
+
 void GrDistanceFieldTextContext::drawText(const GrPaint& paint, const SkPaint& skPaint,
                                           const char text[], size_t byteLength,
                                           SkScalar x, SkScalar y) {
     SkASSERT(byteLength == 0 || text != NULL);
 
     // nothing to draw or can't draw
     if (text == NULL || byteLength == 0 /* no raster clip? || fRC->isEmpty()*/
         || fSkPaint.getRasterizer()) {
         return;
     }
 
     this->init(paint, skPaint);
 
     SkScalar sizeRatio = fTextRatio;
 
     SkDrawCacheProc glyphCacheProc = fSkPaint.getDrawCacheProc();
 
     SkAutoGlyphCache    autoCache(fSkPaint, &fDeviceProperties, NULL);
     SkGlyphCache*       cache = autoCache.getCache();
     GrFontScaler*       fontScaler = GetGrFontScaler(cache);
 
+    setup_gamma_texture(fContext, cache, fDeviceProperties, &fGammaTexture);
+
     // need to measure first
     // TODO - generate positions and pre-load cache as well?
     const char* stop = text + byteLength;
     if (fSkPaint.getTextAlign() != SkPaint::kLeft_Align) {
         SkFixed    stopX = 0;
         SkFixed    stopY = 0;
 
         const char* textPtr = text;
         while (textPtr < stop) {
             // don't need x, y here, since all subpixel variants will have the
@@ skipping 53 matching lines @@
     }
 
     this->init(paint, skPaint);
 
     SkDrawCacheProc glyphCacheProc = fSkPaint.getDrawCacheProc();
 
     SkAutoGlyphCache    autoCache(fSkPaint, &fDeviceProperties, NULL);
     SkGlyphCache*       cache = autoCache.getCache();
     GrFontScaler*       fontScaler = GetGrFontScaler(cache);
 
+    setup_gamma_texture(fContext, cache, fDeviceProperties, &fGammaTexture);
+
     const char*        stop = text + byteLength;
 
     if (SkPaint::kLeft_Align == fSkPaint.getTextAlign()) {
         while (text < stop) {
             // the last 2 parameters are ignored
             const SkGlyph& glyph = glyphCacheProc(cache, &text, 0, 0);
 
             if (glyph.fWidth) {
                 SkScalar x = pos[0];
                 SkScalar y = scalarsPerPosition == 1 ? constY : pos[1];
@@ skipping 23 matching lines @@
                                       SkScalarToFixed(x) - (glyph.fAdvanceX >> alignShift),
                                       SkScalarToFixed(y) - (glyph.fAdvanceY >> alignShift),
                                       fontScaler);
             }
             pos += scalarsPerPosition;
         }
     }
 
     this->finish();
 }