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Draw.c
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Draw.c
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/*
* The Python Imaging Library.
* $Id$
*
* a simple drawing package for the Imaging library
*
* history:
* 1996-04-13 fl Created.
* 1996-04-30 fl Added transforms and polygon support.
* 1996-08-12 fl Added filled polygons.
* 1996-11-05 fl Fixed float/int confusion in polygon filler
* 1997-07-04 fl Support 32-bit images (C++ would have been nice)
* 1998-09-09 fl Eliminated qsort casts; improved rectangle clipping
* 1998-09-10 fl Fixed fill rectangle to include lower edge (!)
* 1998-12-29 fl Added arc, chord, and pieslice primitives
* 1999-01-10 fl Added some level 2 ("arrow") stuff (experimental)
* 1999-02-06 fl Added bitmap primitive
* 1999-07-26 fl Eliminated a compiler warning
* 1999-07-31 fl Pass ink as void* instead of int
* 2002-12-10 fl Added experimental RGBA-on-RGB drawing
* 2004-09-04 fl Support simple wide lines (no joins)
* 2005-05-25 fl Fixed line width calculation
*
* Copyright (c) 1996-2006 by Fredrik Lundh
* Copyright (c) 1997-2006 by Secret Labs AB.
*
* See the README file for information on usage and redistribution.
*/
/* FIXME: support fill/outline attribute for all filled shapes */
/* FIXME: support zero-winding fill */
/* FIXME: add drawing context, support affine transforms */
/* FIXME: support clip window (and mask?) */
#include "Imaging.h"
#include <math.h>
#include <stdint.h>
#define CEIL(v) (int)ceil(v)
#define FLOOR(v) ((v) >= 0.0 ? (int)(v) : (int)floor(v))
#define INK8(ink) (*(UINT8 *)ink)
/*
* Rounds around zero (up=away from zero, down=towards zero)
* This guarantees that ROUND_UP|DOWN(f) == -ROUND_UP|DOWN(-f)
*/
#define ROUND_UP(f) ((int)((f) >= 0.0 ? floor((f) + 0.5F) : -floor(fabs(f) + 0.5F)))
#define ROUND_DOWN(f) ((int)((f) >= 0.0 ? ceil((f)-0.5F) : -ceil(fabs(f) - 0.5F)))
/* -------------------------------------------------------------------- */
/* Primitives */
/* -------------------------------------------------------------------- */
typedef struct {
/* edge descriptor for polygon engine */
int d;
int x0, y0;
int xmin, ymin, xmax, ymax;
float dx;
} Edge;
/* Type used in "polygon*" functions */
typedef void (*hline_handler)(Imaging, int, int, int, int);
static inline void
point8(Imaging im, int x, int y, int ink) {
if (x >= 0 && x < im->xsize && y >= 0 && y < im->ysize) {
if (strncmp(im->mode, "I;16", 4) == 0) {
im->image8[y][x * 2] = (UINT8)ink;
im->image8[y][x * 2 + 1] = (UINT8)ink;
} else {
im->image8[y][x] = (UINT8)ink;
}
}
}
static inline void
point32(Imaging im, int x, int y, int ink) {
if (x >= 0 && x < im->xsize && y >= 0 && y < im->ysize) {
im->image32[y][x] = ink;
}
}
static inline void
point32rgba(Imaging im, int x, int y, int ink) {
unsigned int tmp;
if (x >= 0 && x < im->xsize && y >= 0 && y < im->ysize) {
UINT8 *out = (UINT8 *)im->image[y] + x * 4;
UINT8 *in = (UINT8 *)&ink;
out[0] = BLEND(in[3], out[0], in[0], tmp);
out[1] = BLEND(in[3], out[1], in[1], tmp);
out[2] = BLEND(in[3], out[2], in[2], tmp);
}
}
static inline void
hline8(Imaging im, int x0, int y0, int x1, int ink) {
int pixelwidth;
if (y0 >= 0 && y0 < im->ysize) {
if (x0 < 0) {
x0 = 0;
} else if (x0 >= im->xsize) {
return;
}
if (x1 < 0) {
return;
} else if (x1 >= im->xsize) {
x1 = im->xsize - 1;
}
if (x0 <= x1) {
pixelwidth = strncmp(im->mode, "I;16", 4) == 0 ? 2 : 1;
memset(
im->image8[y0] + x0 * pixelwidth,
(UINT8)ink,
(x1 - x0 + 1) * pixelwidth);
}
}
}
static inline void
hline32(Imaging im, int x0, int y0, int x1, int ink) {
INT32 *p;
if (y0 >= 0 && y0 < im->ysize) {
if (x0 < 0) {
x0 = 0;
} else if (x0 >= im->xsize) {
return;
}
if (x1 < 0) {
return;
} else if (x1 >= im->xsize) {
x1 = im->xsize - 1;
}
p = im->image32[y0];
while (x0 <= x1) {
p[x0++] = ink;
}
}
}
static inline void
hline32rgba(Imaging im, int x0, int y0, int x1, int ink) {
unsigned int tmp;
if (y0 >= 0 && y0 < im->ysize) {
if (x0 < 0) {
x0 = 0;
} else if (x0 >= im->xsize) {
return;
}
if (x1 < 0) {
return;
} else if (x1 >= im->xsize) {
x1 = im->xsize - 1;
}
if (x0 <= x1) {
UINT8 *out = (UINT8 *)im->image[y0] + x0 * 4;
UINT8 *in = (UINT8 *)&ink;
while (x0 <= x1) {
out[0] = BLEND(in[3], out[0], in[0], tmp);
out[1] = BLEND(in[3], out[1], in[1], tmp);
out[2] = BLEND(in[3], out[2], in[2], tmp);
x0++;
out += 4;
}
}
}
}
static inline void
line8(Imaging im, int x0, int y0, int x1, int y1, int ink) {
int i, n, e;
int dx, dy;
int xs, ys;
/* normalize coordinates */
dx = x1 - x0;
if (dx < 0) {
dx = -dx, xs = -1;
} else {
xs = 1;
}
dy = y1 - y0;
if (dy < 0) {
dy = -dy, ys = -1;
} else {
ys = 1;
}
n = (dx > dy) ? dx : dy;
if (dx == 0) {
/* vertical */
for (i = 0; i < dy; i++) {
point8(im, x0, y0, ink);
y0 += ys;
}
} else if (dy == 0) {
/* horizontal */
for (i = 0; i < dx; i++) {
point8(im, x0, y0, ink);
x0 += xs;
}
} else if (dx > dy) {
/* bresenham, horizontal slope */
n = dx;
dy += dy;
e = dy - dx;
dx += dx;
for (i = 0; i < n; i++) {
point8(im, x0, y0, ink);
if (e >= 0) {
y0 += ys;
e -= dx;
}
e += dy;
x0 += xs;
}
} else {
/* bresenham, vertical slope */
n = dy;
dx += dx;
e = dx - dy;
dy += dy;
for (i = 0; i < n; i++) {
point8(im, x0, y0, ink);
if (e >= 0) {
x0 += xs;
e -= dy;
}
e += dx;
y0 += ys;
}
}
}
static inline void
line32(Imaging im, int x0, int y0, int x1, int y1, int ink) {
int i, n, e;
int dx, dy;
int xs, ys;
/* normalize coordinates */
dx = x1 - x0;
if (dx < 0) {
dx = -dx, xs = -1;
} else {
xs = 1;
}
dy = y1 - y0;
if (dy < 0) {
dy = -dy, ys = -1;
} else {
ys = 1;
}
n = (dx > dy) ? dx : dy;
if (dx == 0) {
/* vertical */
for (i = 0; i < dy; i++) {
point32(im, x0, y0, ink);
y0 += ys;
}
} else if (dy == 0) {
/* horizontal */
for (i = 0; i < dx; i++) {
point32(im, x0, y0, ink);
x0 += xs;
}
} else if (dx > dy) {
/* bresenham, horizontal slope */
n = dx;
dy += dy;
e = dy - dx;
dx += dx;
for (i = 0; i < n; i++) {
point32(im, x0, y0, ink);
if (e >= 0) {
y0 += ys;
e -= dx;
}
e += dy;
x0 += xs;
}
} else {
/* bresenham, vertical slope */
n = dy;
dx += dx;
e = dx - dy;
dy += dy;
for (i = 0; i < n; i++) {
point32(im, x0, y0, ink);
if (e >= 0) {
x0 += xs;
e -= dy;
}
e += dx;
y0 += ys;
}
}
}
static inline void
line32rgba(Imaging im, int x0, int y0, int x1, int y1, int ink) {
int i, n, e;
int dx, dy;
int xs, ys;
/* normalize coordinates */
dx = x1 - x0;
if (dx < 0) {
dx = -dx, xs = -1;
} else {
xs = 1;
}
dy = y1 - y0;
if (dy < 0) {
dy = -dy, ys = -1;
} else {
ys = 1;
}
n = (dx > dy) ? dx : dy;
if (dx == 0) {
/* vertical */
for (i = 0; i < dy; i++) {
point32rgba(im, x0, y0, ink);
y0 += ys;
}
} else if (dy == 0) {
/* horizontal */
for (i = 0; i < dx; i++) {
point32rgba(im, x0, y0, ink);
x0 += xs;
}
} else if (dx > dy) {
/* bresenham, horizontal slope */
n = dx;
dy += dy;
e = dy - dx;
dx += dx;
for (i = 0; i < n; i++) {
point32rgba(im, x0, y0, ink);
if (e >= 0) {
y0 += ys;
e -= dx;
}
e += dy;
x0 += xs;
}
} else {
/* bresenham, vertical slope */
n = dy;
dx += dx;
e = dx - dy;
dy += dy;
for (i = 0; i < n; i++) {
point32rgba(im, x0, y0, ink);
if (e >= 0) {
x0 += xs;
e -= dy;
}
e += dx;
y0 += ys;
}
}
}
static int
x_cmp(const void *x0, const void *x1) {
float diff = *((float *)x0) - *((float *)x1);
if (diff < 0) {
return -1;
} else if (diff > 0) {
return 1;
} else {
return 0;
}
}
static void
draw_horizontal_lines(
Imaging im, int n, Edge *e, int ink, int *x_pos, int y, hline_handler hline) {
int i;
for (i = 0; i < n; i++) {
if (e[i].ymin == y && e[i].ymin == e[i].ymax) {
int xmax;
int xmin = e[i].xmin;
if (*x_pos != -1 && *x_pos < xmin) {
// Line would be after the current position
continue;
}
xmax = e[i].xmax;
if (*x_pos > xmin) {
// Line would be partway through x_pos, so increase the starting point
xmin = *x_pos;
if (xmax < xmin) {
// Line would now end before it started
continue;
}
}
(*hline)(im, xmin, e[i].ymin, xmax, ink);
*x_pos = xmax + 1;
}
}
}
/*
* Filled polygon draw function using scan line algorithm.
*/
static inline int
polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler hline, int hasAlpha) {
Edge **edge_table;
float *xx;
int edge_count = 0;
int ymin = im->ysize - 1;
int ymax = 0;
int i, j, k;
float adjacent_line_x, adjacent_line_x_other_edge;
if (n <= 0) {
return 0;
}
/* Initialize the edge table and find polygon boundaries */
/* malloc check ok, using calloc */
edge_table = calloc(n, sizeof(Edge *));
if (!edge_table) {
return -1;
}
for (i = 0; i < n; i++) {
if (ymin > e[i].ymin) {
ymin = e[i].ymin;
}
if (ymax < e[i].ymax) {
ymax = e[i].ymax;
}
if (e[i].ymin == e[i].ymax) {
if (hasAlpha != 1) {
(*hline)(im, e[i].xmin, e[i].ymin, e[i].xmax, ink);
}
continue;
}
edge_table[edge_count++] = (e + i);
}
if (ymin < 0) {
ymin = 0;
}
if (ymax > im->ysize) {
ymax = im->ysize;
}
/* Process the edge table with a scan line searching for intersections */
/* malloc check ok, using calloc */
xx = calloc(edge_count * 2, sizeof(float));
if (!xx) {
free(edge_table);
return -1;
}
for (; ymin <= ymax; ymin++) {
j = 0;
for (i = 0; i < edge_count; i++) {
Edge *current = edge_table[i];
if (ymin >= current->ymin && ymin <= current->ymax) {
xx[j++] = (ymin - current->y0) * current->dx + current->x0;
if (ymin == current->ymax && ymin < ymax) {
// Needed to draw consistent polygons
xx[j] = xx[j - 1];
j++;
} else if (current->dx != 0 && roundf(xx[j-1]) == xx[j-1]) {
// Connect discontiguous corners
for (k = 0; k < i; k++) {
Edge *other_edge = edge_table[k];
if ((current->dx > 0 && other_edge->dx <= 0) ||
(current->dx < 0 && other_edge->dx >= 0)) {
continue;
}
// Check if the two edges join to make a corner
if (((ymin == current->ymin && ymin == other_edge->ymin) ||
(ymin == current->ymax && ymin == other_edge->ymax)) &&
xx[j-1] == (ymin - other_edge->y0) * other_edge->dx + other_edge->x0) {
// Determine points from the edges on the next row
// Or if this is the last row, check the previous row
int offset = ymin == ymax ? -1 : 1;
adjacent_line_x = (ymin + offset - current->y0) * current->dx + current->x0;
adjacent_line_x_other_edge = (ymin + offset - other_edge->y0) * other_edge->dx + other_edge->x0;
if (ymin == current->ymax) {
if (current->dx > 0) {
xx[k] = fmax(adjacent_line_x, adjacent_line_x_other_edge) + 1;
} else {
xx[k] = fmin(adjacent_line_x, adjacent_line_x_other_edge) - 1;
}
} else {
if (current->dx > 0) {
xx[k] = fmin(adjacent_line_x, adjacent_line_x_other_edge);
} else {
xx[k] = fmax(adjacent_line_x, adjacent_line_x_other_edge) + 1;
}
}
break;
}
}
}
}
}
qsort(xx, j, sizeof(float), x_cmp);
if (hasAlpha == 1) {
int x_pos = j == 0 ? -1 : 0;
for (i = 1; i < j; i += 2) {
int x_end = ROUND_DOWN(xx[i]);
if (x_end < x_pos) {
// Line would be before the current position
continue;
}
draw_horizontal_lines(im, n, e, ink, &x_pos, ymin, hline);
if (x_end < x_pos) {
// Line would be before the current position
continue;
}
int x_start = ROUND_UP(xx[i - 1]);
if (x_pos > x_start) {
// Line would be partway through x_pos, so increase the starting point
x_start = x_pos;
if (x_end < x_start) {
// Line would now end before it started
continue;
}
}
(*hline)(im, x_start, ymin, x_end, ink);
x_pos = x_end + 1;
}
draw_horizontal_lines(im, n, e, ink, &x_pos, ymin, hline);
} else {
for (i = 1; i < j; i += 2) {
(*hline)(im, ROUND_UP(xx[i - 1]), ymin, ROUND_DOWN(xx[i]), ink);
}
}
}
free(xx);
free(edge_table);
return 0;
}
static inline int
polygon8(Imaging im, int n, Edge *e, int ink, int eofill) {
return polygon_generic(im, n, e, ink, eofill, hline8, 0);
}
static inline int
polygon32(Imaging im, int n, Edge *e, int ink, int eofill) {
return polygon_generic(im, n, e, ink, eofill, hline32, 0);
}
static inline int
polygon32rgba(Imaging im, int n, Edge *e, int ink, int eofill) {
return polygon_generic(im, n, e, ink, eofill, hline32rgba, 1);
}
static inline void
add_edge(Edge *e, int x0, int y0, int x1, int y1) {
/* printf("edge %d %d %d %d\n", x0, y0, x1, y1); */
if (x0 <= x1) {
e->xmin = x0, e->xmax = x1;
} else {
e->xmin = x1, e->xmax = x0;
}
if (y0 <= y1) {
e->ymin = y0, e->ymax = y1;
} else {
e->ymin = y1, e->ymax = y0;
}
if (y0 == y1) {
e->d = 0;
e->dx = 0.0;
} else {
e->dx = ((float)(x1 - x0)) / (y1 - y0);
if (y0 == e->ymin) {
e->d = 1;
} else {
e->d = -1;
}
}
e->x0 = x0;
e->y0 = y0;
}
typedef struct {
void (*point)(Imaging im, int x, int y, int ink);
void (*hline)(Imaging im, int x0, int y0, int x1, int ink);
void (*line)(Imaging im, int x0, int y0, int x1, int y1, int ink);
int (*polygon)(Imaging im, int n, Edge *e, int ink, int eofill);
} DRAW;
DRAW draw8 = {point8, hline8, line8, polygon8};
DRAW draw32 = {point32, hline32, line32, polygon32};
DRAW draw32rgba = {point32rgba, hline32rgba, line32rgba, polygon32rgba};
/* -------------------------------------------------------------------- */
/* Interface */
/* -------------------------------------------------------------------- */
#define DRAWINIT() \
if (im->image8) { \
draw = &draw8; \
ink = INK8(ink_); \
} else { \
draw = (op) ? &draw32rgba : &draw32; \
memcpy(&ink, ink_, sizeof(ink)); \
}
int
ImagingDrawPoint(Imaging im, int x0, int y0, const void *ink_, int op) {
DRAW *draw;
INT32 ink;
DRAWINIT();
draw->point(im, x0, y0, ink);
return 0;
}
int
ImagingDrawLine(Imaging im, int x0, int y0, int x1, int y1, const void *ink_, int op) {
DRAW *draw;
INT32 ink;
DRAWINIT();
draw->line(im, x0, y0, x1, y1, ink);
return 0;
}
int
ImagingDrawWideLine(
Imaging im, int x0, int y0, int x1, int y1, const void *ink_, int width, int op) {
DRAW *draw;
INT32 ink;
int dx, dy;
double big_hypotenuse, small_hypotenuse, ratio_max, ratio_min;
int dxmin, dxmax, dymin, dymax;
Edge e[4];
DRAWINIT();
dx = x1 - x0;
dy = y1 - y0;
if (dx == 0 && dy == 0) {
draw->point(im, x0, y0, ink);
return 0;
}
big_hypotenuse = hypot(dx, dy);
small_hypotenuse = (width - 1) / 2.0;
ratio_max = ROUND_UP(small_hypotenuse) / big_hypotenuse;
ratio_min = ROUND_DOWN(small_hypotenuse) / big_hypotenuse;
dxmin = ROUND_DOWN(ratio_min * dy);
dxmax = ROUND_DOWN(ratio_max * dy);
dymin = ROUND_DOWN(ratio_min * dx);
dymax = ROUND_DOWN(ratio_max * dx);
{
int vertices[4][2] = {
{x0 - dxmin, y0 + dymax},
{x1 - dxmin, y1 + dymax},
{x1 + dxmax, y1 - dymin},
{x0 + dxmax, y0 - dymin}};
add_edge(e + 0, vertices[0][0], vertices[0][1], vertices[1][0], vertices[1][1]);
add_edge(e + 1, vertices[1][0], vertices[1][1], vertices[2][0], vertices[2][1]);
add_edge(e + 2, vertices[2][0], vertices[2][1], vertices[3][0], vertices[3][1]);
add_edge(e + 3, vertices[3][0], vertices[3][1], vertices[0][0], vertices[0][1]);
draw->polygon(im, 4, e, ink, 0);
}
return 0;
}
int
ImagingDrawRectangle(
Imaging im,
int x0,
int y0,
int x1,
int y1,
const void *ink_,
int fill,
int width,
int op) {
int i;
int y;
int tmp;
DRAW *draw;
INT32 ink;
DRAWINIT();
if (y0 > y1) {
tmp = y0, y0 = y1, y1 = tmp;
}
if (fill) {
if (y0 < 0) {
y0 = 0;
} else if (y0 >= im->ysize) {
return 0;
}
if (y1 < 0) {
return 0;
} else if (y1 > im->ysize) {
y1 = im->ysize;
}
for (y = y0; y <= y1; y++) {
draw->hline(im, x0, y, x1, ink);
}
} else {
/* outline */
if (width == 0) {
width = 1;
}
for (i = 0; i < width; i++) {
draw->hline(im, x0, y0 + i, x1, ink);
draw->hline(im, x0, y1 - i, x1, ink);
draw->line(im, x1 - i, y0 + width, x1 - i, y1 - width + 1, ink);
draw->line(im, x0 + i, y0 + width, x0 + i, y1 - width + 1, ink);
}
}
return 0;
}
int
ImagingDrawPolygon(Imaging im, int count, int *xy, const void *ink_, int fill, int width, int op) {
int i, n, x0, y0, x1, y1;
DRAW *draw;
INT32 ink;
if (count <= 0) {
return 0;
}
DRAWINIT();
if (fill) {
/* Build edge list */
/* malloc check ok, using calloc */
Edge *e = calloc(count, sizeof(Edge));
if (!e) {
(void)ImagingError_MemoryError();
return -1;
}
for (i = n = 0; i < count - 1; i++) {
x0 = xy[i * 2];
y0 = xy[i * 2 + 1];
x1 = xy[i * 2 + 2];
y1 = xy[i * 2 + 3];
if (y0 == y1 && i != 0 && y0 == xy[i * 2 - 1]) {
// This is a horizontal line,
// that immediately follows another horizontal line
Edge *last_e = &e[n-1];
if (x1 > x0 && x0 > xy[i * 2 - 2]) {
// They are both increasing in x
last_e->xmax = x1;
continue;
} else if (x1 < x0 && x0 < xy[i * 2 - 2]) {
// They are both decreasing in x
last_e->xmin = x1;
continue;
}
}
add_edge(&e[n++], x0, y0, x1, y1);
}
if (xy[i * 2] != xy[0] || xy[i * 2 + 1] != xy[1]) {
add_edge(&e[n++], xy[i * 2], xy[i * 2 + 1], xy[0], xy[1]);
}
draw->polygon(im, n, e, ink, 0);
free(e);
} else {
/* Outline */
if (width == 1) {
for (i = 0; i < count - 1; i++) {
draw->line(im, xy[i * 2], xy[i * 2 + 1], xy[i * 2 + 2], xy[i * 2 + 3], ink);
}
draw->line(im, xy[i * 2], xy[i * 2 + 1], xy[0], xy[1], ink);
} else {
for (i = 0; i < count - 1; i++) {
ImagingDrawWideLine(im, xy[i * 2], xy[i * 2 + 1], xy[i * 2 + 2], xy[i * 2 + 3], ink_, width, op);
}
ImagingDrawWideLine(im, xy[i * 2], xy[i * 2 + 1], xy[0], xy[1], ink_, width, op);
}
}
return 0;
}
int
ImagingDrawBitmap(Imaging im, int x0, int y0, Imaging bitmap, const void *ink, int op) {
return ImagingFill2(
im, ink, bitmap, x0, y0, x0 + bitmap->xsize, y0 + bitmap->ysize);
}
/* -------------------------------------------------------------------- */
/* standard shapes */
// Imagine 2D plane and ellipse with center in (0, 0) and semi-major axes a and b.
// Then quarter_* stuff approximates its top right quarter (x, y >= 0) with integer
// points from set {(2x+x0, 2y+y0) | x,y in Z} where x0, y0 are from {0, 1} and
// are such that point (a, b) is in the set.
typedef struct {
int32_t a, b, cx, cy, ex, ey;
int64_t a2, b2, a2b2;
int8_t finished;
} quarter_state;
void
quarter_init(quarter_state *s, int32_t a, int32_t b) {
if (a < 0 || b < 0) {
s->finished = 1;
} else {
s->a = a;
s->b = b;
s->cx = a;
s->cy = b % 2;
s->ex = a % 2;
s->ey = b;
s->a2 = a * a;
s->b2 = b * b;
s->a2b2 = s->a2 * s->b2;
s->finished = 0;
}
}
// deviation of the point from ellipse curve, basically a substitution
// of the point into the ellipse equation
int64_t
quarter_delta(quarter_state *s, int64_t x, int64_t y) {
return llabs(s->a2 * y * y + s->b2 * x * x - s->a2b2);
}
int8_t
quarter_next(quarter_state *s, int32_t *ret_x, int32_t *ret_y) {
if (s->finished) {
return -1;
}
*ret_x = s->cx;
*ret_y = s->cy;
if (s->cx == s->ex && s->cy == s->ey) {
s->finished = 1;
} else {
// Bresenham's algorithm, possible optimization: only consider 2 of 3
// next points depending on current slope
int32_t nx = s->cx;
int32_t ny = s->cy + 2;
int64_t ndelta = quarter_delta(s, nx, ny);
if (nx > 1) {
int64_t newdelta = quarter_delta(s, s->cx - 2, s->cy + 2);
if (ndelta > newdelta) {
nx = s->cx - 2;
ny = s->cy + 2;
ndelta = newdelta;
}
newdelta = quarter_delta(s, s->cx - 2, s->cy);
if (ndelta > newdelta) {
nx = s->cx - 2;
ny = s->cy;
}
}
s->cx = nx;
s->cy = ny;
}
return 0;
}
// quarter_* stuff can "draw" a quarter of an ellipse with thickness 1, great.
// Now we use ellipse_* stuff to join all four quarters of two different sized
// ellipses and receive horizontal segments of a complete ellipse with
// specified thickness.
//
// Still using integer grid with step 2 at this point (like in quarter_*)
// to ease angle clipping in future.
typedef struct {
quarter_state st_o, st_i;
int32_t py, pl, pr;
int32_t cy[4], cl[4], cr[4];
int8_t bufcnt;
int8_t finished;
int8_t leftmost;
} ellipse_state;
void
ellipse_init(ellipse_state *s, int32_t a, int32_t b, int32_t w) {
s->bufcnt = 0;
s->leftmost = a % 2;
quarter_init(&s->st_o, a, b);
if (w < 1 || quarter_next(&s->st_o, &s->pr, &s->py) == -1) {
s->finished = 1;
} else {
s->finished = 0;
quarter_init(&s->st_i, a - 2 * (w - 1), b - 2 * (w - 1));
s->pl = s->leftmost;
}
}
int8_t
ellipse_next(ellipse_state *s, int32_t *ret_x0, int32_t *ret_y, int32_t *ret_x1) {
if (s->bufcnt == 0) {
if (s->finished) {
return -1;
}
int32_t y = s->py;
int32_t l = s->pl;
int32_t r = s->pr;
int32_t cx = 0, cy = 0;
int8_t next_ret;
while ((next_ret = quarter_next(&s->st_o, &cx, &cy)) != -1 && cy <= y) {
}
if (next_ret == -1) {
s->finished = 1;
} else {
s->pr = cx;
s->py = cy;
}
while ((next_ret = quarter_next(&s->st_i, &cx, &cy)) != -1 && cy <= y) {
l = cx;
}
s->pl = next_ret == -1 ? s->leftmost : cx;
if ((l > 0 || l < r) && y > 0) {
s->cl[s->bufcnt] = l == 0 ? 2 : l;
s->cy[s->bufcnt] = y;
s->cr[s->bufcnt] = r;
++s->bufcnt;
}
if (y > 0) {
s->cl[s->bufcnt] = -r;
s->cy[s->bufcnt] = y;
s->cr[s->bufcnt] = -l;
++s->bufcnt;
}
if (l > 0 || l < r) {
s->cl[s->bufcnt] = l == 0 ? 2 : l;
s->cy[s->bufcnt] = -y;
s->cr[s->bufcnt] = r;
++s->bufcnt;
}
s->cl[s->bufcnt] = -r;
s->cy[s->bufcnt] = -y;
s->cr[s->bufcnt] = -l;
++s->bufcnt;
}
--s->bufcnt;
*ret_x0 = s->cl[s->bufcnt];
*ret_y = s->cy[s->bufcnt];
*ret_x1 = s->cr[s->bufcnt];
return 0;
}
// Clipping tree consists of half-plane clipping nodes and combining nodes.
// We can throw a horizontal segment in such a tree and collect an ordered set
// of resulting disjoint clipped segments organized into a sorted linked list
// of their end points.