author Sam Lantinga Sun, 21 Dec 2008 20:16:21 +0000 changeset 2903 e426c4fc9cf7 parent 2902 83c3a4b0e421 child 2904 fa81cc1ef3d0
Working Bresenham line drawing algorithm. We can optimize later, if needed.
 src/video/SDL_draw.h file | annotate | diff | comparison | revisions
```     1.1 --- a/src/video/SDL_draw.h	Sun Dec 21 17:55:02 2008 +0000
1.2 +++ b/src/video/SDL_draw.h	Sun Dec 21 20:16:21 2008 +0000
1.3 @@ -283,49 +283,58 @@
1.4
1.5  #define ABS(_x) ((_x) < 0 ? -(_x) : (_x))
1.6
1.7 -#define SWAP(_x, _y) do { int tmp; tmp = _x; _x = _y; _y = tmp; } while (0)
1.8 -
1.9 -#define BRESENHAM(x0, y0, x1, y1, op) \
1.10 +#define BRESENHAM(x1, y1, x2, y2, op) \
1.11  { \
1.12 -    int deltax, deltay, steep, error, xstep, ystep, x, y; \
1.13 +    int i, deltax, deltay, numpixels; \
1.14 +    int d, dinc1, dinc2; \
1.15 +    int x, xinc1, xinc2; \
1.16 +    int y, yinc1, yinc2; \
1.17   \
1.18 -    deltax = ABS(x1 - x0); \
1.19 -    deltay = ABS(y1 - y0); \
1.20 -    steep = (deltay > deltax); \
1.21 -    if (steep) { \
1.22 -        SWAP(x0, y0); \
1.23 -        SWAP(x1, y1); \
1.24 -        SWAP(deltax, deltay); \
1.25 +    deltax = ABS(x2 - x1); \
1.26 +    deltay = ABS(y2 - y1); \
1.27 + \
1.28 +    if (deltax >= deltay) { \
1.29 +        numpixels = deltax + 1; \
1.30 +        d = (2 * deltay) - deltax; \
1.31 +        dinc1 = deltay * 2; \
1.32 +        dinc2 = (deltay - deltax) * 2; \
1.33 +        xinc1 = 1; \
1.34 +        xinc2 = 1; \
1.35 +        yinc1 = 0; \
1.36 +        yinc2 = 1; \
1.37 +    } else { \
1.38 +        numpixels = deltay + 1; \
1.39 +        d = (2 * deltax) - deltay; \
1.40 +        dinc1 = deltax * 2; \
1.41 +        dinc2 = (deltax - deltay) * 2; \
1.42 +        xinc1 = 0; \
1.43 +        xinc2 = 1; \
1.44 +        yinc1 = 1; \
1.45 +        yinc2 = 1; \
1.46      } \
1.47 -    error = (x1 - x0) / 2; \
1.48 -    y = y0; \
1.49 -    if (x0 > x1) { \
1.50 -        xstep = -1; \
1.51 -    } else { \
1.52 -        xstep = 1; \
1.53 + \
1.54 +    if (x1 > x2) { \
1.55 +        xinc1 = -xinc1; \
1.56 +        xinc2 = -xinc2; \
1.57      } \
1.58 -    if (y0 < y1) { \
1.59 -        ystep = 1; \
1.60 -    } else { \
1.61 -        ystep = -1; \
1.62 +    if (y1 > y2) { \
1.63 +        yinc1 = -yinc1; \
1.64 +        yinc2 = -yinc2; \
1.65      } \
1.66 -    if (!steep) { \
1.67 -        for (x = x0; x != x1; x += xstep) { \
1.68 -            op(x, y); \
1.69 -            error -= deltay; \
1.70 -            if (error < 0) { \
1.71 -                y += ystep; \
1.72 -                error += deltax; \
1.73 -            } \
1.74 -        } \
1.75 -    } else { \
1.76 -        for (x = x0; x != x1; x += xstep) { \
1.77 -            op(y, x); \
1.78 -            error -= deltay; \
1.79 -            if (error < 0) { \
1.80 -                y += ystep; \
1.81 -                error += deltax; \
1.82 -            } \
1.83 + \
1.84 +    x = x1; \
1.85 +    y = y1; \
1.86 + \
1.87 +    for (i = 1; i < numpixels; ++i) { \
1.88 +        op(x, y); \
1.89 +        if (d < 0) { \
1.90 +            d += dinc1; \
1.91 +            x += xinc1; \
1.92 +            y += yinc1; \
1.93 +        } else { \
1.94 +            d += dinc2; \
1.95 +            x += xinc2; \
1.96 +            y += yinc2; \
1.97          } \
1.98      } \
1.99  }
```