Drawing a line code

[Joel]

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;
		}
	}
}
```