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#include <cmath>
#include <vector>
#include <SDL/SDL.h>
#include "resize++.h"
//code adapted by David Olsen from Lanczos filtering article on wikipedia.org
#ifndef M_PI
#define M_PI 3.14159265359
#endif
static inline double Lanczos(double x, int Radius)
{
if (x == 0.0) return 1.0;
if (x <= -Radius || x >= Radius) return 0.0;
double tmp = x * M_PI;
return Radius * std::sin(tmp) * std::sin(tmp / Radius) / (tmp * tmp);
}
static inline void Resample(SDL_Surface * src, SDL_Surface * dst, int filter)
{
const double blur = 1.0;
double factor = dst->w / (double)src->w;
double scale = std::min(factor, 1.0) / blur;
int FilterRadius = filter;
if (filter < 1 )
FilterRadius = 1;
if (filter > 3) //automatically determine fastest filter setting
{
FilterRadius = 3;
if (scale < 0.67) FilterRadius = 2;
if (scale <= 0.5) FilterRadius = 1;
}
double support = FilterRadius / scale;
std::vector<double> contribution_x(std::min((size_t)src->w, 5+(size_t)(2*support)));
/* 5 = room for rounding up in calculations of start, stop and support */
Uint32 ** temp = new Uint32 * [src->h]; //array of source->height * dest->width
for (int i = 0 ; i < src->h; i++)
temp[i] = new Uint32 [dst->w];
if (support <= 0.5) { support = 0.5 + 1E-12; scale = 1.0; }
for (int x = 0; x < dst->w; ++x)
{
double center = (x + 0.5) / factor;
size_t start = (size_t)std::max(center - support + 0.5, (double)0);
size_t stop = (size_t)std::min(center + support + 0.5, (double)src->w);
double density = 0.0;
size_t nmax = stop - start;
double s = start - center + 0.5;
double point[4] = {0,0,0,0};
Uint8 v;
double diff;
for (int y = 0; y < src->h; y++)
{
for (size_t n = 0; n < nmax; ++n)
{
if (y == 0)
{ //only come up with the contribution list once per column.
contribution_x[n] = Lanczos (s * scale, FilterRadius);
density += contribution_x[n];
s++;
}
//it MUST be a 32-bit surface for following code to work correctly
Uint8 * p = (Uint8 *)src->pixels + y * src->pitch + (start+n) * 4;
for (int c = 0; c < 4; c++)
point[c] += p[c] * contribution_x[n];
}
/* Normalize. Truncate to Uint8 values. Place in temp array*/
Uint8 * p = (Uint8 *)&temp[y][x];
for (size_t c = 0; c < 4; c++)
{
if (density != 0.0 && density != 1.0)
point[c] /= density;
if (point[c] < 0)
point[c] = 0;
if (point[c] > 255)
point[c] = 255;
v = (Uint8) point[c];
diff = point[c] - (double)v;
if (diff < 0)
diff = -diff;
if (diff >= 0.5)
v++;
p[c] = v;
point[c] = 0; //reset value for next loop
}
}
}
factor = dst->h / (double)src->h;
scale = std::min(factor, 1.0) / blur;
if (filter > 3) //automatically determine fastest filter setting
{
FilterRadius = 3;
if (scale < 0.67) FilterRadius = 2;
if (scale <= 0.5) FilterRadius = 1;
}
support = FilterRadius / scale;
std::vector<double> contribution_y(std::min((size_t)src->h, 5+(size_t)(2*support)));
if (support <= 0.5) { support = 0.5 + 1E-12; scale = 1.0; }
for (int y = 0; y<dst->h; ++y)
{
double center = (y + 0.5) / factor;
size_t start = (size_t)std::max(center - support + 0.5, (double)0);
size_t stop = (size_t)std::min(center + support + 0.5, (double)src->h);
double density = 0.0;
size_t nmax = stop-start;
double s = start - center+0.5;
double point[4] = {0,0,0,0};
Uint8 v;
double diff;
for (int x=0; x<dst->w; x++)
{
for (size_t n=0; n<nmax; ++n)
{
if (x == 0)
{
contribution_y[n] = Lanczos(s * scale, FilterRadius);
density += contribution_y[n];
s++;
}
Uint8 * p = (Uint8 *)&temp[start+n][x];
for (int c = 0; c < 4; c++)
point[c] += p[c] * contribution_y[n];
}
//destination must also be a 32 bit surface for this to work!
Uint8 * p = (Uint8 *)dst->pixels + y * dst->pitch + x * 4;
for (size_t c = 0; c < 4; c++)
{
if (density != 0.0 && density != 1.0)
point[c] /= density;
if (point[c] < 0)
point[c] = 0;
if (point[c] > 255)
point[c] = 255;
v = (Uint8) point[c];
diff = point[c] - (double)v;
if (diff < 0)
diff = -diff;
if (diff >= 0.5)
v++;
p[c] = v;
point[c] = 0;
}
}
}
//free the temp array, so we don't leak any memory
for (int i = 0 ; i < src->h; i++)
delete [] temp[i];
delete [] temp;
}
static inline Uint32 get_pixel(SDL_Surface *surface, int x, int y)
{
int bpp = surface->format->BytesPerPixel;
/* Here p is the address to the pixel we want to retrieve */
Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
switch(bpp)
{
case 1: return *p;
case 2: return *(Uint16 *)p;
case 3: if(SDL_BYTEORDER == SDL_BIG_ENDIAN)
return p[0] << 16 | p[1] << 8 | p[2];
else
return p[0] | p[1] << 8 | p[2] << 16;
case 4: return *(Uint32 *)p;
default: return 0; /* shouldn't happen, but avoids warnings */
}
}
static inline bool has_alpha(SDL_Surface * src)
{
Uint8 r, g, b, a;
bool is_alpha = false;
if SDL_MUSTLOCK(src) SDL_LockSurface(src);
for (int x = 0; x < src->w; x++)
for (int y = 0; y < src->h; y++)
{
SDL_GetRGBA(get_pixel(src, x, y), src->format, &r, &g, &b, &a);
if (a != SDL_ALPHA_OPAQUE)
{
is_alpha = true;
x = src->w;
break;
}
}
if SDL_MUSTLOCK(src) SDL_UnlockSurface(src);
return is_alpha;
}
SDL_Surface* SDL_Resize(SDL_Surface *src, float factor, bool free, int filter)
{
if (factor > 100.0f) factor = 100.0f; //let's be reasonable...
int new_w = (int)(src->w * factor),
new_h = (int)(src->h * factor);
if (new_w < 1) new_w = 1;
if (new_h < 1) new_h = 1;
return SDL_Resize(src, new_w, new_h, free, filter);
}
SDL_Surface* SDL_Resize(SDL_Surface *src, int new_w, int new_h, bool free, int filter)
{
SDL_Surface * dst;
bool is_alpha = has_alpha(src);
if (src->w == new_w && src->h == new_h)
{
//No change in size. Return an optimized image.
if (is_alpha)
{
dst = SDL_DisplayFormatAlpha(src);
SDL_SetAlpha(src, SDL_SRCALPHA, 0);
}
else
dst = SDL_DisplayFormat(src);
if (free)
SDL_FreeSurface(src);
return dst;
}
Uint32 rmask = 0x000000ff,
gmask = 0x0000ff00,
bmask = 0x00ff0000,
amask = 0xff000000;
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
rmask = 0xff000000;
gmask = 0x00ff0000;
bmask = 0x0000ff00;
amask = 0x000000ff;
#endif
dst = SDL_CreateRGBSurface(0, new_w, new_h, 32, rmask, gmask, bmask, amask);
SDL_Surface * temp = SDL_ConvertSurface(src,dst->format,0);
if (free)
SDL_FreeSurface(src);
src = temp;
Resample(src,dst,filter);
SDL_FreeSurface(temp);
if (is_alpha)
{
temp = SDL_DisplayFormatAlpha(dst);
SDL_SetAlpha(temp, SDL_SRCALPHA, 0);
}
else
temp = SDL_DisplayFormat(dst);
SDL_FreeSurface(dst);
return temp;
}
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