#include <stdio.h>
#include <stdlib.h>

typedef struct {
	int x, y;
	int dx, dy;
	int sx, sy;
	int e;
} Line;

void init_line(
	Line* l,
	const int* f,
	const int* t
) {
	const int dx = abs(t[0] - f[0]);
	const int dy = -abs(t[1] - f[1]);
	l->e = dx + dy;
	l->dx = dx;
	l->dy = dy;
	l->sx = f[0] < t[0]? 1: -1;
	l->sy = f[1] < t[1]? 1: -1;
	l->x = f[0];
	l->y = f[1];
}

void step_line(Line* l) {
	const int e2 = l->e * 2;
	const int dx = l->dx;
	const int dy = l->dy;
	if (e2 > dy) {
		l->e += dy;
		l->x += l->sx;
	}
	if (e2 <= dx) {
		l->e += dx;
		l->y += l->sy;
	}
}

int tri_hand(
	const int* v0,
	const int* v1,
	const int* v2
) {
	return
		(v1[0] - v0[0]) * (v2[1] - v0[1]) -
		(v2[0] - v0[0]) * (v1[1] - v0[1]) > 0;
}

void fill_tri(
	char* buf, int w,
	const int* v0,
	const int* v1,
	const int* v2
) {
	Line ne, fe;
	const int* t;
	int ha, x;
#define swap(a, b) { \
	t = a; \
	a = b; \
	b = t; \
}
	if (v0[1] > v1[1])
		swap(v0, v1);
	if (v1[1] > v2[1])
		swap(v1, v2);
	if (v0[1] > v1[1])
		swap(v0, v1);
#undef swap
	ha = tri_hand(v0, v1, v2);
	if (ha) {
		init_line(&ne, v0, v2);
		init_line(&fe, v0, v1);
	} else {
		init_line(&ne, v0, v1);
		init_line(&fe, v0, v2);
	}
#define scanline \
	for (x = ne.x; x < fe.x; x++) \
		buf[x + fe.y * w] = '#'; \
	step_line(&fe); \
	while (ne.y != fe.y) \
		step_line(&ne);
	while (fe.y < v1[1]) {
		scanline
	}
	if (ha)
		init_line(&fe, v1, v2);
	else
		init_line(&ne, v1, v2);
	while (fe.y < v2[1]) {
		scanline
	}
#undef scanline
}

int main(void) {
	int v0[] = { 16, 2  };
	int v1[] = { 31, 16 };
	int v2[] = { 1,  30 };
	char buf[32*32];
	int i;
	for (i = 0; i < 32*32; i++)
		buf[i] = ' ';
	fill_tri(buf, 32, v0, v1, v2);
	for (i = 0; i < 32*32; i++) {
		if (!(i & 31)) printf("\n");
		printf("%c", buf[i]);
	}
	printf("\n");
}