• Joel (56/56) Nov 06 2022 I found some code on the net but haven't been able to get it
• claptrap (5/7) Nov 06 2022 this is the classic integer line drawing algorithm...
• Joel (4/11) Nov 06 2022 The algorithm is too hard for me to work out and dg2d doesn't
• rikki cattermole (33/35) Nov 06 2022 Its not as complex as that page initially looks.
• Joel (53/89) Nov 07 2022 Ok, this is working:
• rikki cattermole (3/4) Nov 07 2022 I'm glad to hear it!
• z (14/15) Nov 06 2022 You can add a condition to prevent writing out of the
• z (2/3) Nov 06 2022 I meant above or equal(`>=`), woops

Joel <joelcnz gmail.com> writes:

I found some code on the net but haven't been able to get it 
working properly. I trying to draw with mouse (any direction).

```d
	void drawLine(Dot s, Dot e) {
		auto d=s;

/+
		// import std.algorithm : swap;

		if (s.pos.X>e.pos.X) {
			int ox=s.pos.Xi;
			s.pos=Point(e.pos.X,s.pos.Y);
			e.pos=Point(ox,e.pos.Y);
			// swap(s.pos.X, e.pos.X);
		}

		if (s.pos.Y>e.pos.Y) {
			int oy=s.pos.Yi;
			s.pos=Point(s.pos.X,e.pos.Y);
			e.pos=Point(e.pos.X,oy);
			// swap(s.pos.Y, e.pos.Y);
		}
+/
		int x0=s.pos.Xi, x1=e.pos.Xi, y0=s.pos.Yi, y1=e.pos.Yi;
		int dy, dx, incrE, incrNE, dt,x,y;

/+
		import std.algorithm : swap;
		if (x0>x1)
			swap(x0,x1);
		if (y0>y1)
			swap(y0,y1);
+/
		dx = x1 - x0;
		dy = y1 - y0;
		dt = 2 * (dy - dx);
		incrE = 2*dy;
		incrNE = 2*(dy - dx);
		x = x0;
		y = y0;

		d.setPos(s.pos);
		drawDot(d);

		while(x < x1)
		{
			if (dt <= 0)
			{
				dt += incrE;
				x++;
			}
			else
			{
				dt += incrNE;
				x++;
				y++;
			}
			d.setPos(Point(x,y));
			drawDot(d);
		}
	} // drawLine
```

claptrap <clap trap.com> writes:

On Sunday, 6 November 2022 at 11:22:26 UTC, Joel wrote:
 I found some code on the net but haven't been able to get it 
 working properly. I trying to draw with mouse (any direction).

this is the classic integer line drawing algorithm...

https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm#Algorithm_for_integer_arithmetic

or you could use this...

https://github.com/cerjones/dg2d

Joel <joelcnz gmail.com> writes:

On Sunday, 6 November 2022 at 11:40:40 UTC, claptrap wrote:
 On Sunday, 6 November 2022 at 11:22:26 UTC, Joel wrote:
 I found some code on the net but haven't been able to get it 
 working properly. I trying to draw with mouse (any direction).

 this is the classic integer line drawing algorithm...

 https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm#Algorithm_for_integer_arithmetic

 or you could use this...

 https://github.com/cerjones/dg2d

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.

rikki cattermole <rikki cattermole.co.nz> writes:

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.

Joel <joelcnz gmail.com> writes:

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;
		}
	}
}
```

rikki cattermole <rikki cattermole.co.nz> writes:

On 07/11/2022 10:29 PM, Joel wrote:
 Ok, this is working:

I'm glad to hear it!

Pathing algorithms can be quite fun to mess around with.

z <z z.com> writes:

On Sunday, 6 November 2022 at 16:48:24 UTC, Joel wrote:
I want my code fixed up so that works from any two points.

You can add a condition to prevent writing out of the 
image/framebuffer/whatever memory so it won't do any out of 
bounds write.

Another valid algorithm could be testing all pixels for distance 
from the line.(i believe that's what 2D vector rendering software 
does?)

`incrE` and `incrNE`'s use can be replaced with an approach where 
you increment a counter by `dx/dy`(assuming `dy > dx` here) every 
iteration(after you draw the dot i believe) and whenever the 
counter is above `1` you add `sx` or `sy` to the `x` or `y` value 
then substract the counter by `1`.(as the wording implies, you 
will probably need to branch depending on if `dx > dy` or `dy > 
dx`).

z <z z.com> writes:

On Sunday, 6 November 2022 at 20:07:47 UTC, z wrote:
 whenever the counter is above `1`

I meant above or equal(`>=`), woops