i experimented with bresenhams linedraw algorithm a while ago. maybe it's helpful for you:

Code:

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var video_mode=8;

var video_depth=32;



on_f5=null;



string debug;



bmap bmp_arrow=<arrow_blue.pcx>;

bmap bmp_canvas=<canvas.tga>; //1024x768 black



panel canvas

{

	bmap=bmp_canvas;

	flags=d3d,refresh,visible;

}



function putpixel(x,y)

{

	var format;

	var pixel;

	format=bmap_lock(bmp_canvas,0);

	pixel=pixel_for_vec(vector(255,255,255),null,888);

	pixel_to_bmap(bmp_canvas,x,y,pixel);

	bmap_unlock(bmp_canvas);

}



function line(x1,y1,x2,y2) //bresenham algorithm

{

	var x;

	var y;

	var dx;

	var dy;

	var incx; 

	var incy;

	var balance;



	if(x2>=x1)

	{

		dx=x2-x1;

		incx=1;

	}

	else

	{

		dx=x1-x2;

		incx=-1;

	}



	if(y2>=y1)

	{

		dy=y2-y1;

		incy=1;

	}

	else

	{

		dy=y1-y2;

		incy=-1;

	}



	x=x1;

	y=y1;

	

	if(dx>=dy)

	{

		dy=dy<<1;

		balance=dy-dx;

		dx=dx<<1;

		while(x!=x2)

		{

			putpixel(x,y);

			if(balance>=0)

			{

				y+=incy;

				balance-=dx;

			}

			balance+=dy;

			x+=incx;

		}

		putpixel(x,y);

	}

	else

	{

		dx=dx<<1;

		balance=dx-dy;

		dy=dy<<1;

		while(y!=y2)

		{

			putpixel(x,y);

			if(balance>=0)

			{

				x+=incx;

				balance-=dy;

			}

			balance+=dx;

			y+=incy;

		} 

		putpixel(x,y);

	}

}



function main()

{



	var ox;

	var oy;

	var cx;

	var cy;



	mouse_map=bmp_arrow;

	mouse_mode=2;



	while(1)

	{

		mouse_pos.x=pointer.x;

		mouse_pos.y=pointer.y;



		if(mouse_left)

		{

			ox=mouse_pos.x;

			oy=mouse_pos.y;

			while(mouse_left)

			{

				mouse_pos.x=pointer.x;

				mouse_pos.y=pointer.y;



				cx=mouse_pos.x;

				cy=mouse_pos.y;

				line(ox,oy,cx,cy);

				ox=mouse_pos.x;

				oy=mouse_pos.y;

				wait(1);

			}

		}



		wait(1);

	}

}

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