C language bresenhamLine Algorithm - c

Question

I am confused about what could be the problem in this algorithm:
With these parameters:
ine temp = {(Vector){10, 150}, (Vector){120, 40}, polygon->color};
drawaLine(monitor, &temp);
However, when I change the coordinates to 120, 20 it fails:
Line temp = {(Vector){10, 150}, (Vector){120, 20}, polygon->color};
drawaLine(monitor, &temp);
My code is:
int changed = 0;
int x = line->start.x;
int y = line->start.y;
int dx = (line->end.x - line->start.x);
int dy = (line->end.y - line->start.y);
dx = (dx < 0) ? -dx : dx;
dy = (dy < 0) ? -dy : dy;
int signx;
int signy;
if ((line->end.x - line->start.x) == 0) {
signx = 0;
} else {
int tempsignx = (line->end.x - line->start.x);
signx = (tempsignx < 0) ? -1 : 1;
}
if ((line->end.y - line->start.y) == 0) {
signy = 0;
} else {
int tempsingy = (line->end.y - line->start.y);
signy = (tempsingy < 0) ? -1 : 1;
}
//swap values
if (dy > dx) {
int temp = dy;
dy = dx;
dx = temp;
changed = 1; //changed = true
}
int e = 2 * dy - dx;
for (int i = 1; i <= dx; i++) {
Vector temp = {x, y};
drawPixel(monitor, temp, line->color);
while (e >= 0) {
if (changed) {
x = x + signx;
} else {
y = y + signy;
e = e - 2 * dx;
}
}
if (changed) {
y += signy;
} else {
x += signx;
e = e + 2 * dy;
}
Vector x2y2 = {line->end.x, line->end.y};
drawPixel(monitor, x2y2, line->color);
}
}