Move DistanceAdjustTable to its own file

src/gpu/GrAtlasTextContext.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 "GrAtlasTextContext.h"
 
 #include "GrBlurUtils.h"
 #include "GrDrawContext.h"
@@ skipping 28 matching lines @@
 static const int kSmallDFFontSize = 32;
 static const int kSmallDFFontLimit = 32;
 static const int kMediumDFFontSize = 72;
 static const int kMediumDFFontLimit = 72;
 static const int kLargeDFFontSize = 162;
 #ifdef SK_BUILD_FOR_ANDROID
 static const int kLargeDFFontLimit = 384;
 #else
 static const int kLargeDFFontLimit = 2 * kLargeDFFontSize;
 #endif
-
-SkDEBUGCODE(static const int kExpectedDistanceAdjustTableSize = 8;)
 };
 
 GrAtlasTextContext::GrAtlasTextContext(GrContext* context, const SkSurfaceProps& surfaceProps)
     : INHERITED(context, surfaceProps)
-    , fDistanceAdjustTable(new DistanceAdjustTable) {
+    , fDistanceAdjustTable(new GrDistanceFieldAdjustTable) {
     // We overallocate vertices in our textblobs based on the assumption that A8 has the greatest
     // vertexStride
     static_assert(GrAtlasTextBlob::kGrayTextVASize >= GrAtlasTextBlob::kColorTextVASize &&
                   GrAtlasTextBlob::kGrayTextVASize >= GrAtlasTextBlob::kLCDTextVASize,
                   "vertex_attribute_changed");
     fCurrStrike = nullptr;
     fCache = context->getTextBlobCache();
 }
 
-void GrAtlasTextContext::DistanceAdjustTable::buildDistanceAdjustTable() {
-
-    // 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.
-    //
-    // The idea here is that instead of determining the initial (real) coverage and
-    // then adjusting that coverage, we determine an adjusted coverage directly by
-    // essentially manipulating the geometry (in this case, the distance to the glyph
-    // edge). So for black (on assumed white) this thins a bit; for white (on
-    // assumed black) this fake bolds the geometry a bit.
-    //
-    // The distance adjustment is calculated by determining the actual coverage value which
-    // when fed into in the mask gamma table gives us an 'adjusted coverage' value of 0.5. This
-    // actual coverage value (assuming it's between 0 and 1) corresponds to a distance from the
-    // actual edge. So by subtracting this distance adjustment and computing without the
-    // the coverage adjustment we should get 0.5 coverage at the same point.
-    //
-    // This has several implications:
-    //     For non-gray lcd smoothed text, each subpixel essentially is using a
-    //     slightly different geometry.
-    //
-    //     For black (on assumed white) this may not cover some pixels which were
-    //     previously covered; however those pixels would have been only slightly
-    //     covered and that slight coverage would have been decreased anyway. Also, some pixels
-    //     which were previously fully covered may no longer be fully covered.
-    //
-    //     For white (on assumed black) this may cover some pixels which weren't
-    //     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];
-
-    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;
-                break;
-            }
-        }
-    }
-}
 
 GrAtlasTextContext* GrAtlasTextContext::Create(GrContext* context,
                                                const SkSurfaceProps& surfaceProps) {
     return new GrAtlasTextContext(context, surfaceProps);
 }
 
 bool GrAtlasTextContext::canDraw(const SkPaint& skPaint, const SkMatrix& viewMatrix) {
     return this->canDrawAsDistanceFields(skPaint, viewMatrix) ||
            !SkDraw::ShouldDrawTextAsPaths(skPaint, viewMatrix);
 }
@@ skipping 1004 matching lines @@
             gTextContext->createDrawTextBlob(clip, grPaint, skPaint, viewMatrix, text,
                                              static_cast<size_t>(textLen), 0, 0, noClip));
 
     SkScalar transX = static_cast<SkScalar>(random->nextU());
     SkScalar transY = static_cast<SkScalar>(random->nextU());
     const GrAtlasTextBlob::Run::SubRunInfo& info = blob->fRuns[0].fSubRunInfo[0];
     return gTextContext->createBatch(blob, info, textLen, 0, 0, color, transX, transY, skPaint);
 }
 
 #endif