Simple Antialiased-Line Drawing

draw_aa_line.c

                                                     /*#######.
    draw_aa_line.c                                  ########",#:
                                                  #########',##".
    KUBE     : www.kube.io                       ##'##'##".##',##.
    Created  : Dec 21 2013 23:33:03               ## ## ## # ##",#.
    Modified : May 14 2014 16:42:04                ## ## ## ## ##'
                                                    ## ## ## :##
                                                     ## ## ##*/

#include <stdlib.h>

typedef struct	s_point
{
	float		x;
	float		y;
}				t_point;

void			pixel_put(float x, float y, int color, float opacity);


static void		draw_loop_x(t_point *start, t_point *end, int color)
{
	float		derivative;
	t_point		current;

	current.x = (int)start->x;
	current.y = start->y;
	derivative = (end->y - start->y) / (end->x - start->x);
	while ((int)current.x <= (int)end->x)
	{
		pixel_put(current.x, current.y, color,
			current.y - (int)current.y);
		current.y--;
		pixel_put(current.x, current.y, color,
			1 - (current.y - (int)current.y));
		current.y++;
		current.x = current.x + 1;
		current.y = current.y + derivative;
	}
}

static void		draw_loop_y(t_point *start, t_point *end, int color)
{
	float		derivative;
	t_point		current;

	current.x = start->x;
	current.y = (int)start->y;
	derivative = (end->x - start->x) / (end->y - start->y);
	while ((int)current.y <= (int)end->y)
	{
		pixel_put(current.x, current.y, color,
			current.x - (int)current.x);
		current.x--;
		pixel_put(current.x, current.y, color,
			1 - (current.x - (int)current.x));
		current.x++;
		current.x = current.x + derivative;
		current.y = current.y + 1;
	}
}

static void		swap_points(t_point **a, t_point **b)
{
	t_point		*cache_point;

	cache_point = *a;
	*a = *b;
	*b = cache_point;
}

void			draw_line(t_point *a, t_point *b, int color)
{
	if (abs((int)(a->x - b->x)) <= abs((int)(a->y - b->y)))
	{
		if (b->y < a->y)
			swap_points(&a, &b);
		draw_loop_y(a, b, color);
	}
	else
	{
		if (b->x < a->x)
			swap_points(&a, &b);
		draw_loop_x(a, b, color);
	}
}