static void plot_segment_gray(int *img, int w, int h,
float a[2], float b[2], int c)
{
int p[2] = {round(a[0]), round(a[1])};
int q[2] = {round(b[0]), round(b[1])};
struct plot_data d = { img, w, h, c };
traverse_segment(p[0], p[1], q[0], q[1], plot_pixel, &d);
}
// generic function to traverse a segment between two pixels
void traverse_segment(int px, int py, int qx, int qy,
void (*f)(int,int,void*), void *e)
{
if (px == qx && py == qy)
f(px, py, e);
else if (qx + qy < px + py) // bad quadrants
traverse_segment(qx, qy, px, py, f, e);
else {
if (qx - px > qy - py || px - qx > qy - py) { // horizontal
float slope = (qy - py)/(float)(qx - px);
for (int i = 0; i < qx-px; i++)
f(i+px, lrint(py + i*slope), e);
} else { // vertical
float slope = (qx - px)/(float)(qy - py);
for (int j = 0; j <= qy-py; j++)
f(lrint(px + j*slope), j+py, e);
}
}
}
// draw a segment between two points
void traverse_segment(int px, int py, int qx, int qy,
void (*f)(int,int,void*), void *e)
{
if (px == qx && py == qy)
f(px, py, e);
else if (qx + qy < px + py) // bad quadrants
traverse_segment(qx, qy, px, py, f, e);
else {
if (abs(qx - px) > qy - py) { // horitzontal
float slope = (qy - py); slope /= (qx - px);
assert(px < qx);
assert(fabs(slope) <= 1);
for (int i = 0; i < qx-px; i++)
f(i+px, lrint(py + i*slope), e);
} else { // vertical
float slope = (qx - px); slope /= (qy - py);
assert(abs(qy - py) >= abs(qx - px));
assert(py < qy);
assert(fabs(slope) <= 1);
for (int j = 0; j <= qy-py; j++)
f(lrint(px+j*slope), j+py, e);
}
}
}
// function to draw a red segment
static void plot_segment_red(struct image_rgba *f,
double x0, double y0, double xf, double yf)
{
traverse_segment(x0, y0, xf, yf, plot_pixel_red, f);
}
// function to draw a green segment
static void plot_segment_green(struct FTR *f,
double x0, double y0, double xf, double yf)
{
traverse_segment(x0, y0, xf, yf, plot_pixel_green, f);
}
