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#include "SkFontHost.h"
#include <math.h>
// define this to use pre-compiled tables for gamma. This is slightly faster,
// and doesn't create any RW global memory, but means we cannot change the
// gamma at runtime.
#define USE_PREDEFINED_GAMMA_TABLES
#ifndef USE_PREDEFINED_GAMMA_TABLES
// define this if you want to spew out the "C" code for the tables, given
// the current values for SK_BLACK_GAMMA and SK_WHITE_GAMMA.
#define DUMP_GAMMA_TABLESx
#endif
///////////////////////////////////////////////////////////////////////////////
#ifdef USE_PREDEFINED_GAMMA_TABLES
#include "sk_predefined_gamma.h"
#else // use writable globals for gamma tables
static bool gGammaIsBuilt;
static uint8_t gBlackGamma[256], gWhiteGamma[256];
#define SK_BLACK_GAMMA (1.4f)
#define SK_WHITE_GAMMA (1/1.4f)
static void build_power_table(uint8_t table[], float ee)
{
// printf("------ build_power_table %g\n", ee);
for (int i = 0; i < 256; i++)
{
float x = i / 255.f;
// printf(" %d %g", i, x);
x = powf(x, ee);
// printf(" %g", x);
int xx = SkScalarRound(SkFloatToScalar(x * 255));
// printf(" %d\n", xx);
table[i] = SkToU8(xx);
}
}
#ifdef DUMP_GAMMA_TABLES
#include "SkString.h"
static void dump_a_table(const char name[], const uint8_t table[],
float gamma) {
SkDebugf("\n");
SkDebugf("\/\/ Gamma table for %g\n", gamma);
SkDebugf("static const uint8_t %s[] = {\n", name);
for (int y = 0; y < 16; y++) {
SkString line, tmp;
for (int x = 0; x < 16; x++) {
tmp.printf("0x%02X, ", *table++);
line.append(tmp);
}
SkDebugf(" %s\n", line.c_str());
}
SkDebugf("};\n");
}
#endif
#endif
///////////////////////////////////////////////////////////////////////////////
void SkFontHost::GetGammaTables(const uint8_t* tables[2])
{
#ifndef USE_PREDEFINED_GAMMA_TABLES
if (!gGammaIsBuilt)
{
build_power_table(gBlackGamma, SK_BLACK_GAMMA);
build_power_table(gWhiteGamma, SK_WHITE_GAMMA);
gGammaIsBuilt = true;
#ifdef DUMP_GAMMA_TABLES
dump_a_table("gBlackGamma", gBlackGamma, SK_BLACK_GAMMA);
dump_a_table("gWhiteGamma", gWhiteGamma, SK_WHITE_GAMMA);
#endif
}
#endif
tables[0] = gBlackGamma;
tables[1] = gWhiteGamma;
}
// If the luminance is <= this value, then apply the black gamma table
#define BLACK_GAMMA_THRESHOLD 0x40
// If the luminance is >= this value, then apply the white gamma table
#define WHITE_GAMMA_THRESHOLD 0xC0
int SkFontHost::ComputeGammaFlag(const SkPaint& paint)
{
if (paint.getShader() == NULL)
{
SkColor c = paint.getColor();
int r = SkColorGetR(c);
int g = SkColorGetG(c);
int b = SkColorGetB(c);
int luminance = (r * 2 + g * 5 + b) >> 3;
if (luminance <= BLACK_GAMMA_THRESHOLD)
{
// printf("------ black gamma for [%d %d %d]\n", r, g, b);
return SkScalerContext::kGammaForBlack_Flag;
}
if (luminance >= WHITE_GAMMA_THRESHOLD)
{
// printf("------ white gamma for [%d %d %d]\n", r, g, b);
return SkScalerContext::kGammaForWhite_Flag;
}
}
return 0;
}
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