Use floats for mask table for accuracy.
http://codereview.appspot.com/5783099/
git-svn-id: http://skia.googlecode.com/svn/trunk@3374 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index f81f372..e00e33c 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -12,6 +12,7 @@
#include "SkColorPriv.h"
#include "SkDescriptor.h"
#include "SkFDot6.h"
+#include "SkFloatingPoint.h"
#include "SkFontHost.h"
#include "SkMask.h"
#include "SkAdvancedTypefaceMetrics.h"
@@ -55,6 +56,7 @@
//#define DUMP_STRIKE_CREATION
//#define SK_GAMMA_APPLY_TO_A8
+//#define SK_GAMMA_SRGB
#ifndef SK_GAMMA_CONTRAST
#define SK_GAMMA_CONTRAST 0x66
@@ -1063,51 +1065,71 @@
///////////////////////////////////////////////////////////////////////////////
-static int apply_contrast(int srca, int contrast) {
- return srca + (((255 - srca) * contrast * srca) / (255*255));
+#ifdef SK_USE_COLOR_LUMINANCE
+
+static float apply_contrast(float srca, float contrast) {
+ return srca + ((1.0f - srca) * contrast * srca);
}
-static void build_power_table(uint8_t table[], float ee) {
- for (int i = 0; i < 256; i++) {
- float x = i / 255.f;
- x = powf(x, ee);
- int xx = SkScalarRoundToInt(SkFloatToScalar(x * 255));
- table[i] = SkToU8(xx);
+#ifdef SK_GAMMA_SRGB
+static float lin(float per) {
+ if (per <= 0.04045f) {
+ return per / 12.92f;
}
+ return powf((per + 0.055f) / 1.055, 2.4f);
}
-
-static void build_gamma_table(uint8_t table[256], int src) {
- static bool gInit;
- static uint8_t powTable[256], invPowTable[256];
- if (!gInit) {
- const float g = SK_GAMMA_EXPONENT;
- build_power_table(powTable, g);
- build_power_table(invPowTable, 1/g);
- gInit = true;
+static float per(float lin) {
+ if (lin <= 0.0031308f) {
+ return lin * 12.92f;
}
+ return 1.055f * powf(lin, 1.0f / 2.4f) - 0.055f;
+}
+#else //SK_GAMMA_SRGB
+static float lin(float per) {
+ const float g = SK_GAMMA_EXPONENT;
+ return powf(per, g);
+}
+static float per(float lin) {
+ const float g = SK_GAMMA_EXPONENT;
+ return powf(lin, 1.0f / g);
+}
+#endif //SK_GAMMA_SRGB
- const int linSrc = powTable[src];
- const int linDst = 255 - linSrc;
- const int dst = invPowTable[linDst];
+static void build_gamma_table(uint8_t table[256], int srcI) {
+ const float src = (float)srcI / 255.0f;
+ const float linSrc = lin(src);
+ const float linDst = 1.0f - linSrc;
+ const float dst = per(linDst);
// have our contrast value taper off to 0 as the src luminance becomes white
- const int contrast = SK_GAMMA_CONTRAST * (255 - linSrc) / 255;
-
- for (int i = 0; i < 256; ++i) {
- int srca = apply_contrast(i, contrast);
- SkASSERT((unsigned)srca <= 255);
- int dsta = 255 - srca;
+ const float contrast = SK_GAMMA_CONTRAST / 255.0f * linDst;
+ const float step = 1.0f / 256.0f;
- //Calculate the output we want.
- int linOut = (linSrc * srca + dsta * linDst) / 255;
- SkASSERT((unsigned)linOut <= 255);
- int out = invPowTable[linOut];
+ //Remove discontinuity and instability when src is close to dst.
+ if (fabs(src - dst) < 0.01f) {
+ float rawSrca = 0.0f;
+ for (int i = 0; i < 256; ++i, rawSrca += step) {
+ float srca = apply_contrast(rawSrca, contrast);
+ table[i] = sk_float_round2int(255.0f * srca);
+ }
+ } else {
+ float rawSrca = 0.0f;
+ for (int i = 0; i < 256; ++i, rawSrca += step) {
+ float srca = apply_contrast(rawSrca, contrast);
+ SkASSERT(srca <= 1.0f);
+ float dsta = 1 - srca;
- //Undo what the blit blend will do.
- int result = ((255 * out) - (255 * dst)) / (src - dst);
- SkASSERT((unsigned)result <= 255);
+ //Calculate the output we want.
+ float linOut = (linSrc * srca + dsta * linDst);
+ SkASSERT(linOut <= 1.0f);
+ float out = per(linOut);
- table[i] = result;
+ //Undo what the blit blend will do.
+ float result = (out - dst) / (src - dst);
+ SkASSERT(sk_float_round2int(255.0f * result) <= 255);
+
+ table[i] = sk_float_round2int(255.0f * result);
+ }
}
}
@@ -1126,7 +1148,7 @@
return gGammaTables[luminance >> 6];
}
-#ifndef SK_USE_COLOR_LUMINANCE
+#else //SK_USE_COLOR_LUMINANCE
static const uint8_t* getIdentityTable() {
static bool gOnce;
static uint8_t gIdentityTable[256];
@@ -1138,7 +1160,7 @@
}
return gIdentityTable;
}
-#endif
+#endif //SK_USE_COLOR_LUMINANCE
static uint16_t packTriple(unsigned r, unsigned g, unsigned b) {
return SkPackRGB16(r >> 3, g >> 2, b >> 3);