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SDL_gamma.c
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/*
SDL - Simple DirectMedia Layer
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Copyright (C) 1997-2009 Sam Lantinga
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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Sam Lantinga
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slouken@libsdl.org
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*/
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#include "SDL_config.h"
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/* Gamma correction support */
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#include "SDL_sysvideo.h"
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static void
CalculateGammaRamp(float gamma, Uint16 * ramp)
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int i;
/* 0.0 gamma is all black */
if (gamma <= 0.0f) {
for (i = 0; i < 256; ++i) {
ramp[i] = 0;
}
return;
} else
/* 1.0 gamma is identity */
if (gamma == 1.0f) {
for (i = 0; i < 256; ++i) {
ramp[i] = (i << 8) | i;
}
return;
} else
/* Calculate a real gamma ramp */
{
int value;
gamma = 1.0f / gamma;
for (i = 0; i < 256; ++i) {
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value =
(int) (SDL_pow((double) i / 256.0, gamma) * 65535.0 + 0.5);
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if (value > 65535) {
value = 65535;
}
ramp[i] = (Uint16) value;
}
}
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static void
CalculateGammaFromRamp(float *gamma, Uint16 * ramp)
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/* The following is adapted from a post by Garrett Bass on OpenGL
Gamedev list, March 4, 2000.
*/
float sum = 0.0f;
int i, count = 0;
*gamma = 1.0;
for (i = 1; i < 256; ++i) {
if ((ramp[i] != 0) && (ramp[i] != 65535)) {
double B = (double) i / 256.0;
double A = ramp[i] / 65535.0;
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sum += (float) (SDL_log(A) / SDL_log(B));
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count++;
}
}
if (count && sum > 0.0f) {
*gamma = 1.0f / (sum / count);
}
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}
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int
SDL_SetGamma(float red, float green, float blue)
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Uint16 ramp[3][256];
CalculateGammaRamp(red, ramp[0]);
CalculateGammaRamp(green, ramp[1]);
CalculateGammaRamp(blue, ramp[2]);
return SDL_SetGammaRamp(ramp[0], ramp[1], ramp[2]);
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}
/* Calculating the gamma by integrating the gamma ramps isn't exact,
so this function isn't officially supported.
*/
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int
SDL_GetGamma(float *red, float *green, float *blue)
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{
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int succeeded;
Uint16 ramp[3][256];
succeeded = SDL_GetGammaRamp(ramp[0], ramp[1], ramp[2]);
if (succeeded >= 0) {
CalculateGammaFromRamp(red, ramp[0]);
CalculateGammaFromRamp(green, ramp[1]);
CalculateGammaFromRamp(blue, ramp[2]);
}
return succeeded;
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}
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int
SDL_SetGammaRamp(const Uint16 * red, const Uint16 * green,
const Uint16 * blue)
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{
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SDL_VideoDevice *_this = SDL_GetVideoDevice();
int succeeded;
/* Lazily allocate the gamma tables */
if (!SDL_CurrentDisplay.gamma) {
SDL_GetGammaRamp(NULL, NULL, NULL);
}
/* Fill the gamma table with the new values */
if (red) {
SDL_memcpy(&SDL_CurrentDisplay.gamma[0 * 256], red,
256 * sizeof(*SDL_CurrentDisplay.gamma));
}
if (green) {
SDL_memcpy(&SDL_CurrentDisplay.gamma[1 * 256], green,
256 * sizeof(*SDL_CurrentDisplay.gamma));
}
if (blue) {
SDL_memcpy(&SDL_CurrentDisplay.gamma[2 * 256], blue,
256 * sizeof(*SDL_CurrentDisplay.gamma));
}
/* Try to set the gamma ramp in the driver */
succeeded = -1;
if (_this && _this->SetDisplayGammaRamp) {
if (SDL_GetFocusWindow()) {
succeeded =
_this->SetDisplayGammaRamp(_this, SDL_CurrentDisplay.gamma);
} else {
succeeded = 0;
}
} else {
SDL_SetError("Gamma ramp manipulation not supported");
}
return succeeded;
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}
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int
SDL_GetGammaRamp(Uint16 * red, Uint16 * green, Uint16 * blue)
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{
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SDL_VideoDevice *_this = SDL_GetVideoDevice();
/* Lazily allocate the gamma table */
if (!SDL_CurrentDisplay.gamma) {
size_t rampsize = (3 * 256 * sizeof(*SDL_CurrentDisplay.gamma));
SDL_CurrentDisplay.gamma = SDL_malloc(rampsize * 2);
if (!SDL_CurrentDisplay.gamma) {
SDL_OutOfMemory();
return -1;
}
if (_this && _this->GetDisplayGammaRamp) {
/* Get the real hardware gamma */
_this->GetDisplayGammaRamp(_this, SDL_CurrentDisplay.gamma);
} else {
/* Assume an identity gamma */
int i;
for (i = 0; i < 256; ++i) {
SDL_CurrentDisplay.gamma[0 * 256 + i] = (i << 8) | i;
SDL_CurrentDisplay.gamma[1 * 256 + i] = (i << 8) | i;
SDL_CurrentDisplay.gamma[2 * 256 + i] = (i << 8) | i;
}
}
SDL_CurrentDisplay.saved_gamma = SDL_CurrentDisplay.gamma + (3 * 256);
SDL_memcpy(SDL_CurrentDisplay.saved_gamma, SDL_CurrentDisplay.gamma,
rampsize);
}
/* Just copy from our internal table */
if (red) {
SDL_memcpy(red, &SDL_CurrentDisplay.gamma[0 * 256],
256 * sizeof(*red));
}
if (green) {
SDL_memcpy(green, &SDL_CurrentDisplay.gamma[1 * 256],
256 * sizeof(*green));
}
if (blue) {
SDL_memcpy(blue, &SDL_CurrentDisplay.gamma[2 * 256],
256 * sizeof(*blue));
}
return 0;
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}
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/* vi: set ts=4 sw=4 expandtab: */