// ### BOILERPLATE ###
// Orthographic Cube Firmware
// Copyright (C) 2006 Peter Todd <pete@petertodd.org>
// 
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
// 
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
// 
// You should have received a copy of the GNU General Public License along
// with this program; if not, write to the Free Software Foundation, Inc.,
// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
// ### BOILERPLATE ###

// Line list stuff. 

#define abs(a) ((a) >= 0 ? (a) : -(a))
				   
// Draws line i to the display buffer
void draw_line(uint8_t ax, uint8_t ay, uint8_t bx, uint8_t by){
static	int8_t deltax,deltay,error,x,y,ystep,xstep;
static	uint8_t steep;

	// We're using Bresenham's line algorithm for all this.

	steep = 0;
	if (abs(by - ay) > abs(bx - ax))
		steep = 1;
#if 1	
	if (steep){
		// swap ax and ay
		x = ax;
		ax = ay;
		ay = x;

		// swap bx and by
		y = bx;
		bx = by;
		by = y;
	}
#endif
	if (ax > bx){
		// swap bx and ax
		x = bx;
		bx = ax;
		ax = x;

		// swap by and ay
		y = by;
		by = ay;
		ay = y;
	}

	deltax = bx - ax;
	deltay = abs(by - ay);
	
	error = 0;
	y = ay;

	if (ay < by){
		ystep = 1;
	}
	else{
		ystep = -1;
	}

	xstep = ax < bx ? 1 : -1;
	x = ax;
	while (x != (bx + xstep)){
		if (steep){
			display_pset((uint8_t)y,(uint8_t)x);
		}
		else{
			display_pset((uint8_t)x,(uint8_t)y);
		}
		
		error += deltay;

		// !@#$% if that error << 1 is replaced by a multiply, it doesn't work!!
		if ((error << 1) >= deltax){
			y += ystep;
			error -= deltax;
		}
		x += xstep;
	}
}