#include "fitz.h"

#define BBOX_MIN -(1<<20)
#define BBOX_MAX (1<<20)

/* divide and floor towards -inf */
static inline int fz_idiv(int a, int b)
{
	return a < 0 ? (a - b + 1) / b : a / b;
}

/* If AA_BITS is defined, then we assume constant N bits of antialiasing. We
 * will attempt to provide at least that number of bits of accuracy in the
 * antialiasing (to a maximum of 8). If it is defined to be 0 then no
 * antialiasing is done. If it is undefined to we will leave the antialiasing
 * accuracy as a run time choice.
 */

#ifndef AA_BITS
#define AA_SCALE(x) ((x * fz_aa_scale) >> 8)
static int fz_aa_hscale = 17;
static int fz_aa_vscale = 15;
static int fz_aa_scale = 256;
static int fz_aa_level = 8;

#elif AA_BITS > 6
#define AA_SCALE(x) (x)
#define fz_aa_hscale 17
#define fz_aa_vscale 15
#define fz_aa_level 8

#elif AA_BITS > 4
#define AA_SCALE(x) ((x * 255) >> 6)
#define fz_aa_hscale 8
#define fz_aa_vscale 8
#define fz_aa_level 6

#elif AA_BITS > 2
#define AA_SCALE(x) (x * 17)
#define fz_aa_hscale 5
#define fz_aa_vscale 3
#define fz_aa_level 4

#elif AA_BITS > 0
#define AA_SCALE(x) ((x * 255) >> 2)
#define fz_aa_hscale 2
#define fz_aa_vscale 2
#define fz_aa_level 2

#else
#define AA_SCALE(x) (x * 255)
#define fz_aa_hscale 1
#define fz_aa_vscale 1
#define fz_aa_level 0

#endif

int
fz_get_aa_level(void)
{
	return fz_aa_level;
}

void
fz_set_aa_level(int level)
{
#ifdef AA_BITS
	fz_warn("anti-aliasing was compiled with a fixed precision of %d bits", fz_aa_level);
#else
	if (level > 6)
	{
		fz_aa_hscale = 17;
		fz_aa_vscale = 15;
		fz_aa_level = 8;
	}
	else if (level > 4)
	{
		fz_aa_hscale = 8;
		fz_aa_vscale = 8;
		fz_aa_level = 6;
	}
	else if (level > 2)
	{
		fz_aa_hscale = 5;
		fz_aa_vscale = 3;
		fz_aa_level = 4;
	}
	else if (level > 0)
	{
		fz_aa_hscale = 2;
		fz_aa_vscale = 2;
		fz_aa_level = 2;
	}
	else
	{
		fz_aa_hscale = 1;
		fz_aa_vscale = 1;
		fz_aa_level = 0;
	}
	fz_aa_scale = 0xFF00 / (fz_aa_hscale * fz_aa_vscale);
#endif
}

/*
 * Global Edge List -- list of straight path segments for scan conversion
 *
 * Stepping along the edges is with bresenham's line algorithm.
 *
 * See Mike Abrash -- Graphics Programming Black Book (notably chapter 40)
 */

typedef struct fz_edge_s fz_edge;

struct fz_edge_s
{
	int x, e, h, y;
	int adj_up, adj_down;
	int xmove;
	int xdir, ydir; /* -1 or +1 */
};

struct fz_gel_s
{
	fz_bbox clip;
	fz_bbox bbox;
	int cap, len;
	fz_edge *edges;
	int acap, alen;
	fz_edge **active;
};

fz_gel *
fz_new_gel(void)
{
	fz_gel *gel;

	gel = fz_malloc(sizeof(fz_gel));
	gel->cap = 512;
	gel->len = 0;
	gel->edges = fz_calloc(gel->cap, sizeof(fz_edge));

	gel->clip.x0 = gel->clip.y0 = BBOX_MAX;
	gel->clip.x1 = gel->clip.y1 = BBOX_MIN;

	gel->bbox.x0 = gel->bbox.y0 = BBOX_MAX;
	gel->bbox.x1 = gel->bbox.y1 = BBOX_MIN;

	gel->acap = 64;
	gel->alen = 0;
	gel->active = fz_calloc(gel->acap, sizeof(fz_edge*));

	return gel;
}

void
fz_reset_gel(fz_gel *gel, fz_bbox clip)
{
	if (fz_is_infinite_rect(clip))
	{
		gel->clip.x0 = gel->clip.y0 = BBOX_MAX;
		gel->clip.x1 = gel->clip.y1 = BBOX_MIN;
	}
	else {
		gel->clip.x0 = clip.x0 * fz_aa_hscale;
		gel->clip.x1 = clip.x1 * fz_aa_hscale;
		gel->clip.y0 = clip.y0 * fz_aa_vscale;
		gel->clip.y1 = clip.y1 * fz_aa_vscale;
	}

	gel->bbox.x0 = gel->bbox.y0 = BBOX_MAX;
	gel->bbox.x1 = gel->bbox.y1 = BBOX_MIN;

	gel->len = 0;
}

void
fz_free_gel(fz_gel *gel)
{
	fz_free(gel->active);
	fz_free(gel->edges);
	fz_free(gel);
}

fz_bbox
fz_bound_gel(fz_gel *gel)
{
	fz_bbox bbox;
	if (gel->len == 0)
		return fz_empty_bbox;
	bbox.x0 = fz_idiv(gel->bbox.x0, fz_aa_hscale);
	bbox.y0 = fz_idiv(gel->bbox.y0, fz_aa_vscale);
	bbox.x1 = fz_idiv(gel->bbox.x1, fz_aa_hscale) + 1;
	bbox.y1 = fz_idiv(gel->bbox.y1, fz_aa_vscale) + 1;
	return bbox;
}

enum { INSIDE, OUTSIDE, LEAVE, ENTER };

#define clip_lerp_y(v,m,x0,y0,x1,y1,t) clip_lerp_x(v,m,y0,x0,y1,x1,t)

static int
clip_lerp_x(int val, int m, int x0, int y0, int x1, int y1, int *out)
{
	int v0out = m ? x0 > val : x0 < val;
	int v1out = m ? x1 > val : x1 < val;

	if (v0out + v1out == 0)
		return INSIDE;

	if (v0out + v1out == 2)
		return OUTSIDE;

	if (v1out)
	{
		*out = y0 + (y1 - y0) * (val - x0) / (x1 - x0);
		return LEAVE;
	}

	else
	{
		*out = y1 + (y0 - y1) * (val - x1) / (x0 - x1);
		return ENTER;
	}
}

static void
fz_insert_gel_raw(fz_gel *gel, int x0, int y0, int x1, int y1)
{
	fz_edge *edge;
	int dx, dy;
	int winding;
	int width;
	int tmp;

	if (y0 == y1)
		return;

	if (y0 > y1) {
		winding = -1;
		tmp = x0; x0 = x1; x1 = tmp;
		tmp = y0; y0 = y1; y1 = tmp;
	}
	else
		winding = 1;

	if (x0 < gel->bbox.x0) gel->bbox.x0 = x0;
	if (x0 > gel->bbox.x1) gel->bbox.x1 = x0;
	if (x1 < gel->bbox.x0) gel->bbox.x0 = x1;
	if (x1 > gel->bbox.x1) gel->bbox.x1 = x1;

	if (y0 < gel->bbox.y0) gel->bbox.y0 = y0;
	if (y1 > gel->bbox.y1) gel->bbox.y1 = y1;

	if (gel->len + 1 == gel->cap) {
		gel->cap = gel->cap + 512;
		gel->edges = fz_realloc(gel->edges, gel->cap, sizeof(fz_edge));
	}

	edge = &gel->edges[gel->len++];

	dy = y1 - y0;
	dx = x1 - x0;
	width = ABS(dx);

	edge->xdir = dx > 0 ? 1 : -1;
	edge->ydir = winding;
	edge->x = x0;
	edge->y = y0;
	edge->h = dy;
	edge->adj_down = dy;

	/* initial error term going l->r and r->l */
	if (dx >= 0)
		edge->e = 0;
	else
		edge->e = -dy + 1;

	/* y-major edge */
	if (dy >= width) {
		edge->xmove = 0;
		edge->adj_up = width;
	}

	/* x-major edge */
	else {
		edge->xmove = (width / dy) * edge->xdir;
		edge->adj_up = width % dy;
	}
}

void
fz_insert_gel(fz_gel *gel, float fx0, float fy0, float fx1, float fy1)
{
	int x0, y0, x1, y1;
	int d, v;

	fx0 = floorf(fx0 * fz_aa_hscale);
	fx1 = floorf(fx1 * fz_aa_hscale);
	fy0 = floorf(fy0 * fz_aa_vscale);
	fy1 = floorf(fy1 * fz_aa_vscale);

	x0 = CLAMP(fx0, BBOX_MIN, BBOX_MAX);
	y0 = CLAMP(fy0, BBOX_MIN, BBOX_MAX);
	x1 = CLAMP(fx1, BBOX_MIN, BBOX_MAX);
	y1 = CLAMP(fy1, BBOX_MIN, BBOX_MAX);

	d = clip_lerp_y(gel->clip.y0, 0, x0, y0, x1, y1, &v);
	if (d == OUTSIDE) return;
	if (d == LEAVE) { y1 = gel->clip.y0; x1 = v; }
	if (d == ENTER) { y0 = gel->clip.y0; x0 = v; }

	d = clip_lerp_y(gel->clip.y1, 1, x0, y0, x1, y1, &v);
	if (d == OUTSIDE) return;
	if (d == LEAVE) { y1 = gel->clip.y1; x1 = v; }
	if (d == ENTER) { y0 = gel->clip.y1; x0 = v; }

	d = clip_lerp_x(gel->clip.x0, 0, x0, y0, x1, y1, &v);
	if (d == OUTSIDE) {
		x0 = x1 = gel->clip.x0;
	}
	if (d == LEAVE) {
		fz_insert_gel_raw(gel, gel->clip.x0, v, gel->clip.x0, y1);
		x1 = gel->clip.x0;
		y1 = v;
	}
	if (d == ENTER) {
		fz_insert_gel_raw(gel, gel->clip.x0, y0, gel->clip.x0, v);
		x0 = gel->clip.x0;
		y0 = v;
	}

	d = clip_lerp_x(gel->clip.x1, 1, x0, y0, x1, y1, &v);
	if (d == OUTSIDE) {
		x0 = x1 = gel->clip.x1;
	}
	if (d == LEAVE) {
		fz_insert_gel_raw(gel, gel->clip.x1, v, gel->clip.x1, y1);
		x1 = gel->clip.x1;
		y1 = v;
	}
	if (d == ENTER) {
		fz_insert_gel_raw(gel, gel->clip.x1, y0, gel->clip.x1, v);
		x0 = gel->clip.x1;
		y0 = v;
	}

	fz_insert_gel_raw(gel, x0, y0, x1, y1);
}

void
fz_sort_gel(fz_gel *gel)
{
	fz_edge *a = gel->edges;
	int n = gel->len;

	int h, i, k;
	fz_edge t;

	h = 1;
	if (n < 14) {
		h = 1;
	}
	else {
		while (h < n)
			h = 3 * h + 1;
		h /= 3;
		h /= 3;
	}

	while (h > 0)
	{
		for (i = 0; i < n; i++) {
			t = a[i];
			k = i - h;
			/* TODO: sort on y major, x minor */
			while (k >= 0 && a[k].y > t.y) {
				a[k + h] = a[k];
				k -= h;
			}
			a[k + h] = t;
		}

		h /= 3;
	}
}

int
fz_is_rect_gel(fz_gel *gel)
{
	/* a rectangular path is converted into two vertical edges of identical height */
	if (gel->len == 2)
	{
		fz_edge *a = gel->edges + 0;
		fz_edge *b = gel->edges + 1;
		return a->y == b->y && a->h == b->h &&
			a->xmove == 0 && a->adj_up == 0 &&
			b->xmove == 0 && b->adj_up == 0;
	}
	return 0;
}

/*
 * Active Edge List -- keep track of active edges while sweeping
 */

static void
sort_active(fz_edge **a, int n)
{
	int h, i, k;
	fz_edge *t;

	h = 1;
	if (n < 14) {
		h = 1;
	}
	else {
		while (h < n)
			h = 3 * h + 1;
		h /= 3;
		h /= 3;
	}

	while (h > 0)
	{
		for (i = 0; i < n; i++) {
			t = a[i];
			k = i - h;
			while (k >= 0 && a[k]->x > t->x) {
				a[k + h] = a[k];
				k -= h;
			}
			a[k + h] = t;
		}

		h /= 3;
	}
}

static void
insert_active(fz_gel *gel, int y, int *e)
{
	/* insert edges that start here */
	while (*e < gel->len && gel->edges[*e].y == y) {
		if (gel->alen + 1 == gel->acap) {
			int newcap = gel->acap + 64;
			fz_edge **newactive = fz_realloc(gel->active, newcap, sizeof(fz_edge*));
			gel->active = newactive;
			gel->acap = newcap;
		}
		gel->active[gel->alen++] = &gel->edges[(*e)++];
	}

	/* shell-sort the edges by increasing x */
	sort_active(gel->active, gel->alen);
}

static void
advance_active(fz_gel *gel)
{
	fz_edge *edge;
	int i = 0;

	while (i < gel->alen)
	{
		edge = gel->active[i];

		edge->h --;

		/* terminator! */
		if (edge->h == 0) {
			gel->active[i] = gel->active[--gel->alen];
		}

		else {
			edge->x += edge->xmove;
			edge->e += edge->adj_up;
			if (edge->e > 0) {
				edge->x += edge->xdir;
				edge->e -= edge->adj_down;
			}
			i ++;
		}
	}
}

/*
 * Anti-aliased scan conversion.
 */

static inline void add_span_aa(int *list, int x0, int x1, int xofs)
{
	int x0pix, x0sub;
	int x1pix, x1sub;

	if (x0 == x1)
		return;

	/* x between 0 and width of bbox */
	x0 -= xofs;
	x1 -= xofs;

	x0pix = x0 / fz_aa_hscale;
	x0sub = x0 % fz_aa_hscale;
	x1pix = x1 / fz_aa_hscale;
	x1sub = x1 % fz_aa_hscale;

	if (x0pix == x1pix)
	{
		list[x0pix] += x1sub - x0sub;
		list[x0pix+1] += x0sub - x1sub;
	}

	else
	{
		list[x0pix] += fz_aa_hscale - x0sub;
		list[x0pix+1] += x0sub;
		list[x1pix] += x1sub - fz_aa_hscale;
		list[x1pix+1] += -x1sub;
	}
}

static inline void non_zero_winding_aa(fz_gel *gel, int *list, int xofs)
{
	int winding = 0;
	int x = 0;
	int i;
	for (i = 0; i < gel->alen; i++)
	{
		if (!winding && (winding + gel->active[i]->ydir))
			x = gel->active[i]->x;
		if (winding && !(winding + gel->active[i]->ydir))
			add_span_aa(list, x, gel->active[i]->x, xofs);
		winding += gel->active[i]->ydir;
	}
}

static inline void even_odd_aa(fz_gel *gel, int *list, int xofs)
{
	int even = 0;
	int x = 0;
	int i;
	for (i = 0; i < gel->alen; i++)
	{
		if (!even)
			x = gel->active[i]->x;
		else
			add_span_aa(list, x, gel->active[i]->x, xofs);
		even = !even;
	}
}

static inline void undelta_aa(unsigned char * restrict out, int * restrict in, int n)
{
	int d = 0;
	while (n--)
	{
		d += *in++;
		*out++ = AA_SCALE(d);
	}
}

static inline void blit_aa(fz_pixmap *dst, int x, int y,
	unsigned char *mp, int w, unsigned char *color)
{
	unsigned char *dp;
	dp = dst->samples + ( (y - dst->y) * dst->w + (x - dst->x) ) * dst->n;
	if (color)
		fz_paint_span_with_color(dp, mp, dst->n, w, color);
	else
		fz_paint_span(dp, mp, 1, w, 255);
}

static void
fz_scan_convert_aa(fz_gel *gel, int eofill, fz_bbox clip,
	fz_pixmap *dst, unsigned char *color)
{
	unsigned char *alphas;
	int *deltas;
	int y, e;
	int yd, yc;

	int xmin = fz_idiv(gel->bbox.x0, fz_aa_hscale);
	int xmax = fz_idiv(gel->bbox.x1, fz_aa_hscale) + 1;

	int xofs = xmin * fz_aa_hscale;

	int skipx = clip.x0 - xmin;
	int clipn = clip.x1 - clip.x0;

	if (gel->len == 0)
		return;

	assert(clip.x0 >= xmin);
	assert(clip.x1 <= xmax);

	alphas = fz_malloc(xmax - xmin + 1);
	deltas = fz_malloc((xmax - xmin + 1) * sizeof(int));
	memset(deltas, 0, (xmax - xmin + 1) * sizeof(int));

	e = 0;
	y = gel->edges[0].y;
	yc = fz_idiv(y, fz_aa_vscale);
	yd = yc;

	while (gel->alen > 0 || e < gel->len)
	{
		yc = fz_idiv(y, fz_aa_vscale);
		if (yc != yd)
		{
			if (yd >= clip.y0 && yd < clip.y1)
			{
				undelta_aa(alphas, deltas, skipx + clipn);
				blit_aa(dst, xmin + skipx, yd, alphas + skipx, clipn, color);
				memset(deltas, 0, (skipx + clipn) * sizeof(int));
			}
		}
		yd = yc;

		insert_active(gel, y, &e);

		if (yd >= clip.y0 && yd < clip.y1)
		{
			if (eofill)
				even_odd_aa(gel, deltas, xofs);
			else
				non_zero_winding_aa(gel, deltas, xofs);
		}

		advance_active(gel);

		if (gel->alen > 0)
			y ++;
		else if (e < gel->len)
			y = gel->edges[e].y;
	}

	if (yd >= clip.y0 && yd < clip.y1)
	{
		undelta_aa(alphas, deltas, skipx + clipn);
		blit_aa(dst, xmin + skipx, yd, alphas + skipx, clipn, color);
	}

	fz_free(deltas);
	fz_free(alphas);
}

/*
 * Sharp (not anti-aliased) scan conversion
 */

static inline void blit_sharp(int x0, int x1, int y,
	fz_bbox clip, fz_pixmap *dst, unsigned char *color)
{
	unsigned char *dp;
	x0 = CLAMP(x0, dst->x, dst->x + dst->w);
	x1 = CLAMP(x1, dst->x, dst->x + dst->w);
	if (x0 < x1)
	{
		dp = dst->samples + ( (y - dst->y) * dst->w + (x0 - dst->x) ) * dst->n;
		if (color)
			fz_paint_solid_color(dp, dst->n, x1 - x0, color);
		else
			fz_paint_solid_alpha(dp, x1 - x0, 255);
	}
}

static inline void non_zero_winding_sharp(fz_gel *gel, int y,
	fz_bbox clip, fz_pixmap *dst, unsigned char *color)
{
	int winding = 0;
	int x = 0;
	int i;
	for (i = 0; i < gel->alen; i++)
	{
		if (!winding && (winding + gel->active[i]->ydir))
			x = gel->active[i]->x;
		if (winding && !(winding + gel->active[i]->ydir))
			blit_sharp(x, gel->active[i]->x, y, clip, dst, color);
		winding += gel->active[i]->ydir;
	}
}

static inline void even_odd_sharp(fz_gel *gel, int y,
	fz_bbox clip, fz_pixmap *dst, unsigned char *color)
{
	int even = 0;
	int x = 0;
	int i;
	for (i = 0; i < gel->alen; i++)
	{
		if (!even)
			x = gel->active[i]->x;
		else
			blit_sharp(x, gel->active[i]->x, y, clip, dst, color);
		even = !even;
	}
}

static void
fz_scan_convert_sharp(fz_gel *gel, int eofill, fz_bbox clip,
	fz_pixmap *dst, unsigned char *color)
{
	int e = 0;
	int y = gel->edges[0].y;

	while (gel->alen > 0 || e < gel->len)
	{
		insert_active(gel, y, &e);

		if (y >= clip.y0 && y < clip.y1)
		{
			if (eofill)
				even_odd_sharp(gel, y, clip, dst, color);
			else
				non_zero_winding_sharp(gel, y, clip, dst, color);
		}

		advance_active(gel);

		if (gel->alen > 0)
			y ++;
		else if (e < gel->len)
			y = gel->edges[e].y;
	}
}

void
fz_scan_convert(fz_gel *gel, int eofill, fz_bbox clip,
	fz_pixmap *dst, unsigned char *color)
{
	if (fz_aa_level > 0)
		fz_scan_convert_aa(gel, eofill, clip, dst, color);
	else
		fz_scan_convert_sharp(gel, eofill, clip, dst, color);
}