1#include "SkFontHost.h"
2#include <math.h>
3
4// define this to use pre-compiled tables for gamma. This is slightly faster,
5// and doesn't create any RW global memory, but means we cannot change the
6// gamma at runtime.
7//#define USE_PREDEFINED_GAMMA_TABLES
8
9#ifndef USE_PREDEFINED_GAMMA_TABLES
10    // define this if you want to spew out the "C" code for the tables, given
11    // the current values for SK_BLACK_GAMMA and SK_WHITE_GAMMA.
12    #define DUMP_GAMMA_TABLESx
13#endif
14
15///////////////////////////////////////////////////////////////////////////////
16
17#include "SkGraphics.h"
18
19// declared here, so we can link against it elsewhere
20void skia_set_text_gamma(float blackGamma, float whiteGamma);
21
22#ifdef USE_PREDEFINED_GAMMA_TABLES
23
24#include "sk_predefined_gamma.h"
25
26void skia_set_text_gamma(float blackGamma, float whiteGamma) {}
27
28#else   // use writable globals for gamma tables
29
30static void build_power_table(uint8_t table[], float ee) {
31//    SkDebugf("------ build_power_table %g\n", ee);
32    for (int i = 0; i < 256; i++) {
33        float x = i / 255.f;
34        //   printf(" %d %g", i, x);
35        x = powf(x, ee);
36        //   printf(" %g", x);
37        int xx = SkScalarRound(SkFloatToScalar(x * 255));
38        //   printf(" %d\n", xx);
39        table[i] = SkToU8(xx);
40    }
41}
42
43static bool gGammaIsBuilt;
44static uint8_t gBlackGamma[256], gWhiteGamma[256];
45
46static float gBlackGammaCoeff = 1.4f;
47static float gWhiteGammaCoeff = 1/1.4f;
48
49void skia_set_text_gamma(float blackGamma, float whiteGamma) {
50    gBlackGammaCoeff = blackGamma;
51    gWhiteGammaCoeff = whiteGamma;
52    gGammaIsBuilt = false;
53    SkGraphics::SetFontCacheUsed(0);
54    build_power_table(gBlackGamma, gBlackGammaCoeff);
55    build_power_table(gWhiteGamma, gWhiteGammaCoeff);
56}
57
58#ifdef DUMP_GAMMA_TABLES
59
60#include "SkString.h"
61
62static void dump_a_table(const char name[], const uint8_t table[],
63                         float gamma) {
64    SkDebugf("\n");
65    SkDebugf("\/\/ Gamma table for %g\n", gamma);
66    SkDebugf("static const uint8_t %s[] = {\n", name);
67    for (int y = 0; y < 16; y++) {
68        SkString line, tmp;
69        for (int x = 0; x < 16; x++) {
70            tmp.printf("0x%02X, ", *table++);
71            line.append(tmp);
72        }
73        SkDebugf("    %s\n", line.c_str());
74    }
75    SkDebugf("};\n");
76}
77
78#endif
79
80#endif
81
82///////////////////////////////////////////////////////////////////////////////
83
84void SkFontHost::GetGammaTables(const uint8_t* tables[2]) {
85#ifndef USE_PREDEFINED_GAMMA_TABLES
86    if (!gGammaIsBuilt) {
87        build_power_table(gBlackGamma, gBlackGammaCoeff);
88        build_power_table(gWhiteGamma, gWhiteGammaCoeff);
89        gGammaIsBuilt = true;
90
91#ifdef DUMP_GAMMA_TABLES
92        dump_a_table("gBlackGamma", gBlackGamma, gBlackGammaCoeff);
93        dump_a_table("gWhiteGamma", gWhiteGamma, gWhiteGammaCoeff);
94#endif
95    }
96#endif
97    tables[0] = gBlackGamma;
98    tables[1] = gWhiteGamma;
99}
100
101// If the luminance is <= this value, then apply the black gamma table
102#define BLACK_GAMMA_THRESHOLD   0x40
103
104// If the luminance is >= this value, then apply the white gamma table
105#define WHITE_GAMMA_THRESHOLD   0xC0
106
107int SkFontHost::ComputeGammaFlag(const SkPaint& paint) {
108    if (paint.getShader() == NULL) {
109        SkColor c = paint.getColor();
110        int r = SkColorGetR(c);
111        int g = SkColorGetG(c);
112        int b = SkColorGetB(c);
113        int luminance = (r * 2 + g * 5 + b) >> 3;
114
115        if (luminance <= BLACK_GAMMA_THRESHOLD) {
116        //    printf("------ black gamma for [%d %d %d]\n", r, g, b);
117            return SkScalerContext::kGammaForBlack_Flag;
118        }
119        if (luminance >= WHITE_GAMMA_THRESHOLD) {
120        //    printf("------ white gamma for [%d %d %d]\n", r, g, b);
121            return SkScalerContext::kGammaForWhite_Flag;
122        }
123    }
124    return 0;
125}
126
127