1
2/*
3 * Copyright 2011 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8#include "SkFontHost.h"
9#include <math.h>
10
11// define this to use pre-compiled tables for gamma. This is slightly faster,
12// and doesn't create any RW global memory, but means we cannot change the
13// gamma at runtime.
14//#define USE_PREDEFINED_GAMMA_TABLES
15
16#ifndef USE_PREDEFINED_GAMMA_TABLES
17    // define this if you want to spew out the "C" code for the tables, given
18    // the current values for SK_BLACK_GAMMA and SK_WHITE_GAMMA.
19    #define DUMP_GAMMA_TABLESx
20#endif
21
22///////////////////////////////////////////////////////////////////////////////
23
24#include "SkGraphics.h"
25
26// declared here, so we can link against it elsewhere
27void skia_set_text_gamma(float blackGamma, float whiteGamma);
28
29#ifdef USE_PREDEFINED_GAMMA_TABLES
30
31#include "sk_predefined_gamma.h"
32
33void skia_set_text_gamma(float blackGamma, float whiteGamma) {}
34
35#else   // use writable globals for gamma tables
36
37static void build_power_table(uint8_t table[], float ee) {
38//    SkDebugf("------ build_power_table %g\n", ee);
39    for (int i = 0; i < 256; i++) {
40        float x = i / 255.f;
41        //   printf(" %d %g", i, x);
42        x = powf(x, ee);
43        //   printf(" %g", x);
44        int xx = SkScalarRound(SkFloatToScalar(x * 255));
45        //   printf(" %d\n", xx);
46        table[i] = SkToU8(xx);
47    }
48}
49
50static bool gGammaIsBuilt;
51static uint8_t gBlackGamma[256], gWhiteGamma[256];
52
53static float gBlackGammaCoeff = 1.4f;
54static float gWhiteGammaCoeff = 1/1.4f;
55
56void skia_set_text_gamma(float blackGamma, float whiteGamma) {
57    gBlackGammaCoeff = blackGamma;
58    gWhiteGammaCoeff = whiteGamma;
59    gGammaIsBuilt = false;
60    SkGraphics::PurgeFontCache();
61    build_power_table(gBlackGamma, gBlackGammaCoeff);
62    build_power_table(gWhiteGamma, gWhiteGammaCoeff);
63}
64
65#ifdef DUMP_GAMMA_TABLES
66
67#include "SkString.h"
68
69static void dump_a_table(const char name[], const uint8_t table[],
70                         float gamma) {
71    SkDebugf("\n");
72    SkDebugf("\/\/ Gamma table for %g\n", gamma);
73    SkDebugf("static const uint8_t %s[] = {\n", name);
74    for (int y = 0; y < 16; y++) {
75        SkString line, tmp;
76        for (int x = 0; x < 16; x++) {
77            tmp.printf("0x%02X, ", *table++);
78            line.append(tmp);
79        }
80        SkDebugf("    %s\n", line.c_str());
81    }
82    SkDebugf("};\n");
83}
84
85#endif
86
87#endif
88
89///////////////////////////////////////////////////////////////////////////////
90
91void SkFontHost::GetGammaTables(const uint8_t* tables[2]) {
92#ifndef USE_PREDEFINED_GAMMA_TABLES
93    if (!gGammaIsBuilt) {
94        build_power_table(gBlackGamma, gBlackGammaCoeff);
95        build_power_table(gWhiteGamma, gWhiteGammaCoeff);
96        gGammaIsBuilt = true;
97
98#ifdef DUMP_GAMMA_TABLES
99        dump_a_table("gBlackGamma", gBlackGamma, gBlackGammaCoeff);
100        dump_a_table("gWhiteGamma", gWhiteGamma, gWhiteGammaCoeff);
101#endif
102    }
103#endif
104    tables[0] = gBlackGamma;
105    tables[1] = gWhiteGamma;
106}
107
108