1 /**

     2  * test/demos/pmc/sdl.cc

     3  * Copyright (C) 2008 Markus Broeker

     4  */

     5 

     6 #include <SDL/SDL.h>

     7 

     8 #define max(a,b) (((a) > (b)) ? (a) : (b))

     9 #define min(a,b) (((a) < (b)) ? (a) : (b))

    10 #define abs(a) (((a)<0) ? -(a) : (a))

    11 #define sign(a) (((a)<0) ? -1 : (a)>0 ? 1 : 0)

    12 

    13 void drawLine (SDL_Surface * s, int x1, int y1, int x2, int y2, Uint32 color)

    14 {

    15     int d;

    16     int x;

    17     int y;

    18     int ax;

    19     int ay;

    20     int sx;

    21     int sy;

    22     int dx;

    23     int dy;

    24 

    25     Uint8 *lineAddr;

    26     Sint32 yOffset;

    27 

    28     dx = x2 - x1;

    29     ax = abs (dx) << 1;

    30     sx = sign (dx);

    31 

    32     dy = y2 - y1;

    33     ay = abs (dy) << 1;

    34     sy = sign (dy);

    35     yOffset = sy * s->pitch;

    36 

    37     x = x1;

    38     y = y1;

    39 

    40     lineAddr = ((Uint8 *) s->pixels) + (y * s->pitch);

    41     if (ax > ay) {              /* x dominant */

    42         d = ay - (ax >> 1);

    43         for (;;) {

    44             *((Uint16 *) (lineAddr + (x << 1))) = (Uint16) color;

    45 

    46             if (x == x2) {

    47                 return;

    48             }

    49             if (d >= 0) {

    50                 y += sy;

    51                 lineAddr += yOffset;

    52                 d -= ax;

    53             }

    54             x += sx;

    55             d += ay;

    56         }

    57     } else {                    /* y dominant */

    58         d = ax - (ay >> 1);

    59         for (;;) {

    60             *((Uint16 *) (lineAddr + (x << 1))) = (Uint16) color;

    61 

    62             if (y == y2) {

    63                 return;

    64             }

    65             if (d >= 0) {

    66                 x += sx;

    67                 d -= ay;

    68             }

    69             y += sy;

    70             lineAddr += yOffset;

    71             d += ax;

    72         }

    73     }

    74 }