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rjm_texbleed.h
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rjm_texbleed.h
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// rjm_texbleed.h
//
// Fills in the color of pixels where alpha==0.
//
// To generate the implementation, place this define in exactly one source
// file before including the header:
// #define TEXBLEED_IMPLEMENTATION
// This is free and unencumbered software released into the public domain.
//
// Anyone is free to copy, modify, publish, use, compile, sell, or
// distribute this software, either in source code form or as a compiled
// binary, for any purpose, commercial or non-commercial, and by any
// means.
//
// In jurisdictions that recognize copyright laws, the author or authors
// of this software dedicate any and all copyright interest in the
// software to the public domain. We make this dedication for the benefit
// of the public at large and to the detriment of our heirs and
// successors. We intend this dedication to be an overt act of
// relinquishment in perpetuity of all present and future rights to this
// software under copyright law.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
// OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
// For more information, please refer to <http://unlicense.org/>
#ifndef __RJM_TEXBLEED_H__
#define __RJM_TEXBLEED_H__
// Given an RGBA texture of w*h, finds all pixels
// where alpha==0 and fills in a suitable RGB color for it.
//
// ac = index of the byte within the pixel that contains the alpha channel.
// pixstride = size of one pixel, in bytes.
// rowstride = size of one row of pixels, in bytes.
void rjm_texbleed(unsigned char *pixels, int w, int h, int ac, int pixstride, int rowstride);
//--- Implementation follows ----------------------------------------------
#ifdef TEXBLEED_IMPLEMENTATION
// We search for pixels with alpha greater than this
// to bleed outwards from.
#define BLEED_THRESHOLD 128
typedef struct { int dx, dy; } TbPoint;
static void bleedcompare(TbPoint *p, int gstride, int offsetx, int offsety)
{
TbPoint other = p[offsety*gstride + offsetx];
other.dx += offsetx;
other.dy += offsety;
int odist = other.dx*other.dx + other.dy*other.dy;
int pdist = p->dx*p->dx + p->dy*p->dy;
if (odist < pdist)
*p = other;
}
void rjm_texbleed(unsigned char *pixels, int w, int h, int ac, int pixstride, int rowstride)
{
int gstride = w + 2;
int cellcount = gstride*(h+2);
TbPoint *storage = (TbPoint *)malloc(cellcount*sizeof(TbPoint));
TbPoint *grid = storage + gstride + 1;
// Initialize to empty.
for (int n=0;n<cellcount;n++)
storage[n].dx = storage[n].dy = 9999;
// Fill in the solid pixels.
int any = 0;
for (int y=0;y<h;y++)
{
for (int x=0;x<w;x++)
{
unsigned char *pix = pixels + y*rowstride + x*pixstride;
if (pix[ac] > BLEED_THRESHOLD) {
TbPoint *p = &grid[y*gstride+x];
p->dx = 0;
p->dy = 0;
any = 1;
}
}
}
if (any)
{
// Distance field sweep - Pass 0
for (int y=0;y<h;y++)
{
for (int x=0;x<w;x++)
{
TbPoint *p = &grid[y*gstride + x];
bleedcompare(p, gstride, -1, 0);
bleedcompare(p, gstride, 0, -1);
bleedcompare(p, gstride, -1, -1);
bleedcompare(p, gstride, 1, -1);
}
for (int x=w-1;x>=0;x--)
{
TbPoint *p = &grid[y*gstride + x];
bleedcompare(p, gstride, 1, 0);
}
}
// Distance field sweep - Pass 1
for (int y=h-1;y>=0;y--)
{
for (int x=w-1;x>=0;x--)
{
TbPoint *p = &grid[y*gstride + x];
bleedcompare(p, gstride, 1, 0);
bleedcompare(p, gstride, 0, 1);
bleedcompare(p, gstride, -1, 1);
bleedcompare(p, gstride, 1, 1);
}
for (int x=0;x<w;x++)
{
TbPoint *p = &grid[y*gstride + x];
bleedcompare(p, gstride, -1, 0);
}
}
// Read back the nearest pixels.
for (int y=0;y<h;y++)
{
for (int x=0;x<w;x++)
{
TbPoint *p = &grid[y*gstride+x];
int sx = x + p->dx;
int sy = y + p->dy;
// Copy the RGB over.
unsigned char *src = pixels + sy*rowstride + sx*pixstride;
unsigned char *dst = pixels + y*rowstride + x*pixstride;
if (dst[ac] == 0) {
for (int n=0;n<pixstride;n++)
dst[n] = src[n];
dst[ac] = 0;
}
}
}
}
free(storage);
}
#endif // TEXBLEED_IMPLEMENTATION
#endif // __RJM_TEXBLEED_H__