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 #ifdef USE_PREDEFINED_GAMMA_TABLES
18
19 #include "sk_predefined_gamma.h"
20
21 #else // use writable globals for gamma tables
22
23 static bool gGammaIsBuilt;
24 static uint8_t gBlackGamma[256], gWhiteGamma[256];
25
26 #define SK_BLACK_GAMMA (1.4f)
27 #define SK_WHITE_GAMMA (1/1.4f)
28
build_power_table(uint8_t table[],float ee)29 static void build_power_table(uint8_t table[], float ee)
30 {
31 // printf("------ build_power_table %g\n", ee);
32 for (int i = 0; i < 256; i++)
33 {
34 float x = i / 255.f;
35 // printf(" %d %g", i, x);
36 x = powf(x, ee);
37 // printf(" %g", x);
38 int xx = SkScalarRound(SkFloatToScalar(x * 255));
39 // printf(" %d\n", xx);
40 table[i] = SkToU8(xx);
41 }
42 }
43
44 #ifdef DUMP_GAMMA_TABLES
45
46 #include "SkString.h"
47
dump_a_table(const char name[],const uint8_t table[],float gamma)48 static void dump_a_table(const char name[], const uint8_t table[],
49 float gamma) {
50 SkDebugf("\n");
51 SkDebugf("\/\/ Gamma table for %g\n", gamma);
52 SkDebugf("static const uint8_t %s[] = {\n", name);
53 for (int y = 0; y < 16; y++) {
54 SkString line, tmp;
55 for (int x = 0; x < 16; x++) {
56 tmp.printf("0x%02X, ", *table++);
57 line.append(tmp);
58 }
59 SkDebugf(" %s\n", line.c_str());
60 }
61 SkDebugf("};\n");
62 }
63
64 #endif
65
66 #endif
67
68 ///////////////////////////////////////////////////////////////////////////////
69
GetGammaTables(const uint8_t * tables[2])70 void SkFontHost::GetGammaTables(const uint8_t* tables[2])
71 {
72 #ifndef USE_PREDEFINED_GAMMA_TABLES
73 if (!gGammaIsBuilt)
74 {
75 build_power_table(gBlackGamma, SK_BLACK_GAMMA);
76 build_power_table(gWhiteGamma, SK_WHITE_GAMMA);
77 gGammaIsBuilt = true;
78
79 #ifdef DUMP_GAMMA_TABLES
80 dump_a_table("gBlackGamma", gBlackGamma, SK_BLACK_GAMMA);
81 dump_a_table("gWhiteGamma", gWhiteGamma, SK_WHITE_GAMMA);
82 #endif
83 }
84 #endif
85 tables[0] = gBlackGamma;
86 tables[1] = gWhiteGamma;
87 }
88
89 // If the luminance is <= this value, then apply the black gamma table
90 #define BLACK_GAMMA_THRESHOLD 0x40
91
92 // If the luminance is >= this value, then apply the white gamma table
93 #define WHITE_GAMMA_THRESHOLD 0xC0
94
ComputeGammaFlag(const SkPaint & paint)95 int SkFontHost::ComputeGammaFlag(const SkPaint& paint)
96 {
97 if (paint.getShader() == NULL)
98 {
99 SkColor c = paint.getColor();
100 int r = SkColorGetR(c);
101 int g = SkColorGetG(c);
102 int b = SkColorGetB(c);
103 int luminance = (r * 2 + g * 5 + b) >> 3;
104
105 if (luminance <= BLACK_GAMMA_THRESHOLD)
106 {
107 // printf("------ black gamma for [%d %d %d]\n", r, g, b);
108 return SkScalerContext::kGammaForBlack_Flag;
109 }
110 if (luminance >= WHITE_GAMMA_THRESHOLD)
111 {
112 // printf("------ white gamma for [%d %d %d]\n", r, g, b);
113 return SkScalerContext::kGammaForWhite_Flag;
114 }
115 }
116 return 0;
117 }
118
119