sRGB support for distance field text.

src/gpu/text/GrDistanceFieldAdjustTable.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDistanceFieldAdjustTable.h"
 
 #include "SkScalerContext.h"
 
 SkDEBUGCODE(static const int kExpectedDistanceAdjustTableSize = 8;)
 
-void GrDistanceFieldAdjustTable::buildDistanceAdjustTable() {
+SkScalar* build_distance_adjust_table(SkScalar paintGamma, SkScalar deviceGamma) {
     // This is used for an approximation of the mask gamma hack, used by raster and bitmap
     // text. The mask gamma hack is based off of guessing what the blend color is going to
     // be, and adjusting the mask so that when run through the linear blend will
     // produce the value closest to the desired result. However, in practice this means
     // that the 'adjusted' mask is just increasing or decreasing the coverage of
     // the mask depending on what it is thought it will blit against. For black (on
     // assumed white) this means that coverages are decreased (on a curve). For white (on
     // assumed black) this means that coverages are increased (on a a curve). At
     // middle (perceptual) gray (which could be blit against anything) the coverages
     // remain the same.
@@ skipping 23 matching lines @@
     //     previously covered at all.
 
     int width, height;
     size_t size;
 
 #ifdef SK_GAMMA_CONTRAST
     SkScalar contrast = SK_GAMMA_CONTRAST;
 #else
     SkScalar contrast = 0.5f;
 #endif
-    SkScalar paintGamma = SK_GAMMA_EXPONENT;
-    SkScalar deviceGamma = SK_GAMMA_EXPONENT;
 
     size = SkScalerContext::GetGammaLUTSize(contrast, paintGamma, deviceGamma,
         &width, &height);
 
     SkASSERT(kExpectedDistanceAdjustTableSize == height);
-    fTable = new SkScalar[height];
+    SkScalar* table = new 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
                 const float kDistanceFieldAAFactor = 0.65f; // should match SK_DistanceFieldAAFactor
                 float d = 2.0f*kDistanceFieldAAFactor*t - kDistanceFieldAAFactor;
 
-                fTable[row] = d;
+                table[row] = d;
                 break;
             }
         }
     }
+
+    return table;
 }
+
+void GrDistanceFieldAdjustTable::buildDistanceAdjustTables() {
+    fTable = build_distance_adjust_table(SK_GAMMA_EXPONENT, SK_GAMMA_EXPONENT);
+    fSRGBTable = build_distance_adjust_table(SK_Scalar1, SK_Scalar1);
+}