Chromium Code Reviews
chromiumcodereview-hr@appspot.gserviceaccount.com (chromiumcodereview-hr) | Please choose your nickname with Settings | Help | Chromium Project | Gerrit Changes | Sign out
(192)

Side by Side Diff: src/gpu/GrDistanceFieldAdjustTable.cpp

Issue 1521453002: Move all text stuff to its own folder (Closed) Base URL: https://skia.googlesource.com/skia.git@cleanuptext11textutils2
Patch Set: Created 5 years ago
Use n/p to move between diff chunks; N/P to move between comments. Draft comments are only viewable by you.
Jump to:
View unified diff | Download patch
« no previous file with comments | « src/gpu/GrDistanceFieldAdjustTable.h ('k') | src/gpu/GrDrawContext.cpp » ('j') | no next file with comments »
Toggle Intra-line Diffs ('i') | Expand Comments ('e') | Collapse Comments ('c') | Show Comments Hide Comments ('s')
OLDNEW
(Empty)
1 /*
2 * Copyright 2015 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #include "GrDistanceFieldAdjustTable.h"
9
10 #include "SkScalerContext.h"
11
12 SkDEBUGCODE(static const int kExpectedDistanceAdjustTableSize = 8;)
13
14 void GrDistanceFieldAdjustTable::buildDistanceAdjustTable() {
15 // This is used for an approximation of the mask gamma hack, used by raster and bitmap
16 // text. The mask gamma hack is based off of guessing what the blend color i s going to
17 // be, and adjusting the mask so that when run through the linear blend will
18 // produce the value closest to the desired result. However, in practice thi s means
19 // that the 'adjusted' mask is just increasing or decreasing the coverage of
20 // the mask depending on what it is thought it will blit against. For black (on
21 // assumed white) this means that coverages are decreased (on a curve). For white (on
22 // assumed black) this means that coverages are increased (on a a curve). At
23 // middle (perceptual) gray (which could be blit against anything) the cover ages
24 // remain the same.
25 //
26 // The idea here is that instead of determining the initial (real) coverage and
27 // then adjusting that coverage, we determine an adjusted coverage directly by
28 // essentially manipulating the geometry (in this case, the distance to the glyph
29 // edge). So for black (on assumed white) this thins a bit; for white (on
30 // assumed black) this fake bolds the geometry a bit.
31 //
32 // The distance adjustment is calculated by determining the actual coverage value which
33 // when fed into in the mask gamma table gives us an 'adjusted coverage' val ue of 0.5. This
34 // actual coverage value (assuming it's between 0 and 1) corresponds to a di stance from the
35 // actual edge. So by subtracting this distance adjustment and computing wit hout the
36 // the coverage adjustment we should get 0.5 coverage at the same point.
37 //
38 // This has several implications:
39 // For non-gray lcd smoothed text, each subpixel essentially is using a
40 // slightly different geometry.
41 //
42 // For black (on assumed white) this may not cover some pixels which wer e
43 // previously covered; however those pixels would have been only slightl y
44 // covered and that slight coverage would have been decreased anyway. Al so, some pixels
45 // which were previously fully covered may no longer be fully covered.
46 //
47 // For white (on assumed black) this may cover some pixels which weren't
48 // previously covered at all.
49
50 int width, height;
51 size_t size;
52
53 #ifdef SK_GAMMA_CONTRAST
54 SkScalar contrast = SK_GAMMA_CONTRAST;
55 #else
56 SkScalar contrast = 0.5f;
57 #endif
58 SkScalar paintGamma = SK_GAMMA_EXPONENT;
59 SkScalar deviceGamma = SK_GAMMA_EXPONENT;
60
61 size = SkScalerContext::GetGammaLUTSize(contrast, paintGamma, deviceGamma,
62 &width, &height);
63
64 SkASSERT(kExpectedDistanceAdjustTableSize == height);
65 fTable = new SkScalar[height];
66
67 SkAutoTArray<uint8_t> data((int)size);
68 SkScalerContext::GetGammaLUTData(contrast, paintGamma, deviceGamma, data.get ());
69
70 // find the inverse points where we cross 0.5
71 // binsearch might be better, but we only need to do this once on creation
72 for (int row = 0; row < height; ++row) {
73 uint8_t* rowPtr = data.get() + row*width;
74 for (int col = 0; col < width - 1; ++col) {
75 if (rowPtr[col] <= 127 && rowPtr[col + 1] >= 128) {
76 // compute point where a mask value will give us a result of 0.5
77 float interp = (127.5f - rowPtr[col]) / (rowPtr[col + 1] - rowPt r[col]);
78 float borderAlpha = (col + interp) / 255.f;
79
80 // compute t value for that alpha
81 // this is an approximate inverse for smoothstep()
82 float t = borderAlpha*(borderAlpha*(4.0f*borderAlpha - 6.0f) + 5 .0f) / 3.0f;
83
84 // compute distance which gives us that t value
85 const float kDistanceFieldAAFactor = 0.65f; // should match SK_D istanceFieldAAFactor
86 float d = 2.0f*kDistanceFieldAAFactor*t - kDistanceFieldAAFactor ;
87
88 fTable[row] = d;
89 break;
90 }
91 }
92 }
93 }
OLDNEW
« no previous file with comments | « src/gpu/GrDistanceFieldAdjustTable.h ('k') | src/gpu/GrDrawContext.cpp » ('j') | no next file with comments »

Powered by Google App Engine
This is Rietveld 408576698