# Re: Drawing a line code

On Sunday, 6 November 2022 at 17:15:03 UTC, rikki cattermole wrote:
```On 07/11/2022 5:48 AM, Joel wrote:
```
The algorithm is too hard for me to work out and dg2d doesn't help either. I want my code fixed up so that works from any two points.
```
Its not as complex as that page initially looks.

```
plotLine(x0, y0, x1, y1)
dx = abs(x1 - x0)
sx = x0 < x1 ? 1 : -1
dy = -abs(y1 - y0)
sy = y0 < y1 ? 1 : -1
error = dx + dy

while true
plot(x0, y0)
if x0 == x1 && y0 == y1 break
e2 = 2 * error
if e2 >= dy
if x0 == x1 break
error = error + dy
x0 = x0 + sx
end if
if e2 <= dx
if y0 == y1 break
error = error + dx
y0 = y0 + sy
end if
end while
```

That is the pseudo code you want.

Its just a matter of typing the variables to something like int.

I can recommend:

https://www.amazon.com/Computer-Graphics-Principles-Practice-3rd/dp/0321399528

and

https://www.amazon.com/Computer-Graphics-C-Version-2nd/dp/0135309247

(The updated version should be fine too)

If you wish to understand it.
```
```
Ok, this is working:

```d
void drawLine(Dot s, Dot e) {
Dot d=s;
int x0=s.pos.Xi, y0=s.pos.Yi;
int x1=e.pos.Xi, y1=e.pos.Yi;

int dx = abs(x1 - x0);
int sx = x0 < x1 ? 1 : -1;
int dy = -abs(y1 - y0);
int sy = y0 < y1 ? 1 : -1;
int error = dx + dy;

while(true) {
d.setPos(Point(x0,y0));
drawDot(d);
if (x0 == x1 && y0 == y1)
break;
int e2 = 2 * error;
if (e2 >= dy) {
if (x0 == x1) break;
error = error + dy;
x0 = x0 + sx;
}
if (e2 <= dx) {
if (y0 == y1) break;
error = error + dx;
y0 = y0 + sy;
}
}
}
//[...]
void mouseDraw(ref Dot d) {
int lmx=g_mx, lmy=g_my, mx,my;
int mstate = SDL_GetMouseState(&mx,&my);
if (mstate & SDL_BUTTON_LEFT) {
if (mx>0 && my>0) {
g_mx=mx/3;
g_my=my/3;
auto s=d, e=d;
s.setPos(Point(lmx, lmy));
e.setPos(Point(g_mx, g_my));
//mixin(tce("lmx lmy g_mx g_my".split));
g_df.drawLine(s,e);
}
} else {
if (mx>0 && my>0) {
g_mx=mx/3;
g_my=my/3;
}
}
}
```
```