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scale.cpp
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scale.cpp
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/*
Copyright (c) 2013 Auston Sterling
See license.txt for copying permission.
-----Image Scaling Library Implementation-----
Auston Sterling
A library containing a variety of algorithms for scaling images.
*/
#ifndef _scale_cpp_
#define _scale_cpp_
#include "SDL/SDL.h"
//Nearest Neighbor scaling, taking in a pointer to the source surface
//and the scaling ratios, returning the new surface, which must
//be manually cleaned up by the user.
SDL_Surface* scaleNN(SDL_Surface* inimage, float xratio, float yratio)
{
//Verify ratios
if (xratio < 0.00001 || yratio < 0.00001) {return NULL;}
//Calculate X and Y for new surface
int x = inimage->w*xratio;
int y = inimage->h*yratio;
//Find inverses of ratios
float invxr = 1/xratio;
float invyr = 1/yratio;
//Create the new surface
SDL_Surface* outimage = SDL_CreateRGBSurface(SDL_SWSURFACE, x, y, inimage->format->BitsPerPixel, 0, 0, 0, 0);
//Lock surfaces
if (SDL_MUSTLOCK(inimage)) {SDL_LockSurface(inimage);}
if (SDL_MUSTLOCK(outimage)) {SDL_LockSurface(outimage);}
//Extract pixels
Uint32* inpixels = (Uint32*)inimage->pixels;
Uint32* outpixels = (Uint32*)outimage->pixels;
//Cycle through all pixels in the output image
for (int j = 0; j < y; j++)
{
for (int i = 0; i < x; i++)
{
outpixels[(j*x)+i] = inpixels[int((int(j*invyr)*inimage->w)+int(i*invxr))];
}
}
//Unlock surfaces
if(SDL_MUSTLOCK(inimage)) {SDL_UnlockSurface(inimage);}
if(SDL_MUSTLOCK(outimage)) {SDL_UnlockSurface(outimage);}
//Color key the new image if needed
if (inimage->flags & SDL_SRCCOLORKEY)
{
SDL_SetColorKey(outimage, SDL_RLEACCEL | SDL_SRCCOLORKEY, inimage->format->colorkey);
}
//Return the SDL_Surface*
return outimage;
}
//Bilinear scaling function, taking in a source image, scaling ratios,
//and returning a pointer to a new surface.
SDL_Surface* scaleBL(SDL_Surface* inimage, float xratio, float yratio)
{
//Verify ratios
if (xratio < 0.00001 || yratio < 0.00001) {return NULL;}
//Calculate X and Y for new surface
int x = inimage->w*xratio;
int y = inimage->h*yratio;
//Find inverses of ratios
float invxr = 1/xratio;
float invyr = 1/yratio;
//Create the new surface
SDL_Surface* outimage = SDL_CreateRGBSurface(SDL_SWSURFACE, x, y, inimage->format->BitsPerPixel, 0, 0, 0, 0);
//Lock surfaces
if (SDL_MUSTLOCK(inimage)) {SDL_LockSurface(inimage);}
if (SDL_MUSTLOCK(outimage)) {SDL_LockSurface(outimage);}
//Extract pixels
Uint32* inpixels = (Uint32*)inimage->pixels;
Uint32* outpixels = (Uint32*)outimage->pixels;
//Reusable vars
float xorig;
float yorig;
int xfloor;
int yfloor;
Uint32 pix[2][2];
Uint8 rgb[5][3];
float xpart1;
float xpart2;
float ypart1;
float ypart2;
//Cycle through all pixels in the output image
for (int j = 0; j < y; j++)
{
for (int i = 0; i < x; i++)
{
//Find corresponding point in source
xorig = float(i) * invxr;
yorig = float(j) * invyr;
//Find top left pixel coordinates
xfloor = int(xorig);
yfloor = int(yorig);
//Store pixel values themselves
pix[0][0] = inpixels[(yfloor * inimage->w) + xfloor];
pix[1][0] = inpixels[(yfloor * inimage->w) + xfloor + 1];
pix[0][1] = inpixels[((yfloor + 1) * inimage->w) + xfloor];
pix[1][1] = inpixels[((yfloor + 1) * inimage->w) + xfloor + 1];
//Extract RGB values
rgb[0][0] = Uint8(pix[0][0] >> 16);
rgb[0][1] = Uint8(pix[0][0] >> 8);
rgb[0][2] = Uint8(pix[0][0] >> 0);
rgb[1][0] = Uint8(pix[1][0] >> 16);
rgb[1][1] = Uint8(pix[1][0] >> 8);
rgb[1][2] = Uint8(pix[1][0] >> 0);
rgb[2][0] = Uint8(pix[0][1] >> 16);
rgb[2][1] = Uint8(pix[0][1] >> 8);
rgb[2][2] = Uint8(pix[0][1] >> 0);
rgb[3][0] = Uint8(pix[1][1] >> 16);
rgb[3][1] = Uint8(pix[1][1] >> 8);
rgb[3][2] = Uint8(pix[1][1] >> 0);
//Calculate intermediate values
xpart1 = xfloor - xorig + 1;
xpart2 = xorig - xfloor;
ypart1 = yfloor - yorig + 1;
ypart2 = yorig - yfloor;
rgb[4][0] = (rgb[0][0] * xpart1 * ypart1) +
(rgb[1][0] * xpart2 * ypart1) +
(rgb[2][0] * xpart1 * ypart2) +
(rgb[3][0] * xpart2 * ypart2);
rgb[4][1] = (rgb[0][1] * xpart1 * ypart1) +
(rgb[1][1] * xpart2 * ypart1) +
(rgb[2][1] * xpart1 * ypart2) +
(rgb[3][1] * xpart2 * ypart2);
rgb[4][2] = (rgb[0][2] * xpart1 * ypart1) +
(rgb[1][2] * xpart2 * ypart1) +
(rgb[2][2] * xpart1 * ypart2) +
(rgb[3][2] * xpart2 * ypart2);
//Copy it over to the destination image
outpixels[(j * x) + i] = SDL_MapRGB(outimage->format,
rgb[4][0], rgb[4][1], rgb[4][2]);
}
}
//Unlock surfaces
if(SDL_MUSTLOCK(inimage)) {SDL_UnlockSurface(inimage);}
if(SDL_MUSTLOCK(outimage)) {SDL_UnlockSurface(outimage);}
//Color key the new image if needed
if (inimage->flags & SDL_SRCCOLORKEY)
{
SDL_SetColorKey(outimage, SDL_RLEACCEL | SDL_SRCCOLORKEY, inimage->format->colorkey);
}
//Return the SDL_Surface*
return outimage;
}
//Helper function, computes the value of the color at the given ratio between the
//two other points
SDL_Color bspline(SDL_Color p1, SDL_Color p2, SDL_Color p3, SDL_Color p4, float t)
{
//Fill in spline formula
int r = ((1-t)*(1-t)*(1-t)*p1.r)/6 +
((3*t*t*t) - (6*t*t) + 4)*p2.r/6 +
((-3*t*t*t) + (3*t*t) + (3*t) + 1)*p3.r/6 +
(t*t*t*p4.r)/6;
int g = ((1-t)*(1-t)*(1-t)*p1.g)/6 +
((3*t*t*t) - (6*t*t) + 4)*p2.g/6 +
((-3*t*t*t) + (3*t*t) + (3*t) + 1)*p3.g/6 +
(t*t*t*p4.g)/6;
int b = ((1-t)*(1-t)*(1-t)*p1.b)/6 +
((3*t*t*t) - (6*t*t) + 4)*p2.b/6 +
((-3*t*t*t) + (3*t*t) + (3*t) + 1)*p3.b/6 +
(t*t*t*p4.b)/6;
//Copy values out and return
SDL_Color ret;
ret.r = r; ret.g = g; ret.b = b;
return ret;
}
//Converts a Uint32 in form ARGB to a SDL_Color
SDL_Color toColor(Uint32 incolor)
{
//Create the SDL_Color
SDL_Color outcolor;
//Copy over values
outcolor.r = incolor >> 16;
outcolor.g = incolor >> 8;
outcolor.b = incolor >> 0;
//Return it
return outcolor;
}
//Bicubic scale
SDL_Surface* scaleBC(SDL_Surface* inimage, float xratio, float yratio)
{
//Verify ratios
if (xratio < 0.00001 || yratio < 0.00001) {return NULL;}
//Calculate X and Y for new surface
int x = inimage->w*xratio;
int y = inimage->h*yratio;
//Find inverses of ratios
float invxr = 1/xratio;
float invyr = 1/yratio;
//Create the new surface
SDL_Surface* outimage = SDL_CreateRGBSurface(SDL_SWSURFACE, x, y, inimage->format->BitsPerPixel, 0, 0, 0, 0);
//Lock surfaces
if (SDL_MUSTLOCK(inimage)) {SDL_LockSurface(inimage);}
if (SDL_MUSTLOCK(outimage)) {SDL_LockSurface(outimage);}
//Extract pixels
Uint32* inpixels = (Uint32*)inimage->pixels;
Uint32* outpixels = (Uint32*)outimage->pixels;
//Other variables
float xorig, yorig;
int xfloor, yfloor;
//Cycle through all pixels in the output image
for (int j = 0; j < y; j++)
{
for (int i = 0; i < x; i++)
{
//Find corresponding point in source
xorig = float(i) * invxr;
yorig = float(j) * invyr;
//Find top left pixel coordinates
xfloor = int(xorig);
yfloor = int(yorig);
//Call bspline on what's needed
//Calls within calls to handle bilinearity
SDL_Color newcolor;
newcolor = bspline(bspline(toColor(inpixels[((yfloor-1<0?0:yfloor-1) * inimage->w) + (xfloor-1<0?0:xfloor-1)]),
toColor(inpixels[((yfloor-1<0?0:yfloor-1) * inimage->w) + (xfloor<0?0:xfloor)]),
toColor(inpixels[((yfloor-1<0?0:yfloor-1) * inimage->w) + (xfloor+1>=inimage->h?inimage->h-1:xfloor+1)]),
toColor(inpixels[((yfloor-1<0?0:yfloor-1) * inimage->w) + (xfloor+2>=inimage->h?inimage->h-1:xfloor+2)]), xorig-xfloor),
bspline(toColor(inpixels[((yfloor<0?0:yfloor) * inimage->w) + (xfloor-1<0?0:xfloor-1)]),
toColor(inpixels[((yfloor<0?0:yfloor) * inimage->w) + (xfloor<0?0:xfloor)]),
toColor(inpixels[((yfloor<0?0:yfloor) * inimage->w) + (xfloor+1>=inimage->h?inimage->h-1:xfloor+1)]),
toColor(inpixels[((yfloor<0?0:yfloor) * inimage->w) + (xfloor+2>=inimage->h?inimage->h-1:xfloor+2)]), xorig-xfloor),
bspline(toColor(inpixels[((yfloor+1>=inimage->w?inimage->w-1:yfloor+1) * inimage->w) + (xfloor-1<0?0:xfloor-1)]),
toColor(inpixels[((yfloor+1>=inimage->w?inimage->w-1:yfloor+1) * inimage->w) + (xfloor<0?0:xfloor)]),
toColor(inpixels[((yfloor+1>=inimage->w?inimage->w-1:yfloor+1) * inimage->w) + (xfloor+1>=inimage->h?inimage->h-1:xfloor+1)]),
toColor(inpixels[((yfloor+1>=inimage->w?inimage->w-1:yfloor+1) * inimage->w) + (xfloor+2>=inimage->h?inimage->h-1:xfloor+2)]), xorig-xfloor),
bspline(toColor(inpixels[((yfloor+2>=inimage->w?inimage->w-1:yfloor+2) * inimage->w) + (xfloor-1<0?0:xfloor-1)]),
toColor(inpixels[((yfloor+2>=inimage->w?inimage->w-1:yfloor+2) * inimage->w) + (xfloor<0?0:xfloor)]),
toColor(inpixels[((yfloor+2>=inimage->w?inimage->w-1:yfloor+2) * inimage->w) + (xfloor+1>=inimage->h?inimage->h-1:xfloor+1)]),
toColor(inpixels[((yfloor+2>=inimage->w?inimage->w-1:yfloor+2) * inimage->w) + (xfloor+2>=inimage->h?inimage->h-1:xfloor+2)]), xorig-xfloor),
yorig-yfloor);
//Write the output pixel
outpixels[(j * x) + i] = SDL_MapRGB(outimage->format, newcolor.r, newcolor.g, newcolor.b);
}
}
//Unlock surfaces
if(SDL_MUSTLOCK(inimage)) {SDL_UnlockSurface(inimage);}
if(SDL_MUSTLOCK(outimage)) {SDL_UnlockSurface(outimage);}
//Color key the new image if needed
if (inimage->flags & SDL_SRCCOLORKEY)
{
SDL_SetColorKey(outimage, SDL_RLEACCEL | SDL_SRCCOLORKEY, inimage->format->colorkey);
}
//Return the SDL_Surface*
return outimage;
}
#endif