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Link: http://codepad.org/HW38iTUH    [ raw code | output | fork ]

mohit_at_codepad - C, pasted on Jun 18: 
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// Simple line drawing function
#include <stdio.h>
#include <math.h>

#define WIDTH  1000
#define HEIGHT 1000
void setPixel(int x, int y) {
  printf("setting (%d, %d) @ videomem[%d] = 1\n", x, y, WIDTH * y + x);
}

void drawLine(int xFrom, int yFrom, int xTo, int yTo) {
  // assert(0 <= xFrom && xFrom <= WIDTH); same for xTo, yFrom and yTo
  // More possible parameter is width of line
  int dx = xTo - xFrom;
  int dy = yTo - yFrom;
  double slope = (0 == dx) ? 0.0 : dy * 1.0 / dx; // FIXME:: INF
  double invslope = (0 == dy) ? 0.0 : dx * 1.0 / dy; // FIXME:: INF
  if( abs(dx) >= abs(dy) ) {
    int f = dx > 0 ? xFrom : xTo;
    int t = xFrom ^ xTo ^ f;
    int x;
    for(x = f; x <= t; ++x) setPixel(x
                                    , (int)( (x-xFrom) * slope + yFrom + 0.5) );
  } else { // assert(dy);
    int f = dy > 0 ? yFrom : yTo;
    int t = yFrom ^ yTo ^ f;
    int y;
    for(y = f; y <= t; ++y) setPixel( (int)( (y-yFrom) * invslope + xFrom + 0.5)
                                    , y );
  }
}

int main() {
#define drawLine_(X0,Y0,X1,Y1) do {printf("\ndrawLine(%d, %d, %d, %d):\n", X0, Y0, X1, Y1); drawLine(X0, Y0, X1, Y1); } while(0)
  drawLine_(0, 0, 0, 0);
  drawLine_(0, 0, 0, 1);
  drawLine_(0, 0, 1, 0);
  drawLine_(0, 1, 0, 0);
  drawLine_(1, 0, 0, 0);
  drawLine_(0, 0, 1, 1);
  drawLine_(1, 1, 0, 0);
  drawLine_(10, 15, 17, 27);
}


Output: 
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drawLine(0, 0, 0, 0):
setting (0, 0) @ videomem[0] = 1

drawLine(0, 0, 0, 1):
setting (0, 0) @ videomem[0] = 1
setting (0, 1) @ videomem[1000] = 1

drawLine(0, 0, 1, 0):
setting (0, 0) @ videomem[0] = 1
setting (1, 0) @ videomem[1] = 1

drawLine(0, 1, 0, 0):
setting (0, 0) @ videomem[0] = 1
setting (0, 1) @ videomem[1000] = 1

drawLine(1, 0, 0, 0):
setting (0, 0) @ videomem[0] = 1
setting (1, 0) @ videomem[1] = 1

drawLine(0, 0, 1, 1):
setting (0, 0) @ videomem[0] = 1
setting (1, 1) @ videomem[1001] = 1

drawLine(1, 1, 0, 0):
setting (0, 0) @ videomem[0] = 1
setting (1, 1) @ videomem[1001] = 1

drawLine(10, 15, 17, 27):
setting (10, 15) @ videomem[15010] = 1
setting (11, 16) @ videomem[16011] = 1
setting (11, 17) @ videomem[17011] = 1
setting (12, 18) @ videomem[18012] = 1
setting (12, 19) @ videomem[19012] = 1
setting (13, 20) @ videomem[20013] = 1
setting (14, 21) @ videomem[21014] = 1
setting (14, 22) @ videomem[22014] = 1
setting (15, 23) @ videomem[23015] = 1
setting (15, 24) @ videomem[24015] = 1
setting (16, 25) @ videomem[25016] = 1
setting (16, 26) @ videomem[26016] = 1
setting (17, 27) @ videomem[27017] = 1


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