pngdriver/polygon.c

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/*!
   \file lib/pngdriver/polygon.c
 
   \brief GRASS png display driver - draw polygon
 
   SPDX-FileCopyrightText: 2003-2014 Per Henrik Johansen
   SPDX-FileCopyrightText: GRASS Development Team
   SPDX-License-Identifier: GPL-2.0-or-later
 
   \author Per Henrik Johansen (original contributor)
   \author Glynn Clements
 */
 
#include <stdlib.h>
#include <math.h>
#include <grass/gis.h>
 
#include "path.h"
#include "pngdriver.h"
 
static int cmp_double(const void *aa, const void *bb)
{
    const double *a = aa;
    const double *b = bb;
 
    return *a > *b ? 1 : *a < *b ? -1 : 0;
}
 
static void fill(double x0, double x1, double y)
{
    int yi = (int)floor(y);
    int xi0 = (int)floor(x0 + 0.5);
    int xi1 = (int)floor(x1 + 0.5);
    unsigned int *p;
    int x;
 
    if (yi >= png.clip_bot || yi < png.clip_top)
        return;
 
    if (xi0 > png.clip_rite)
        return;
 
    if (xi1 < png.clip_left)
        return;
 
    if (xi0 < png.clip_left)
        xi0 = png.clip_left;
 
    if (xi1 > png.clip_rite)
        xi1 = png.clip_rite;
 
    p = &png.grid[yi * png.width + xi0];
 
    for (x = xi0; x < xi1; x++)
        *p++ = png.current_color;
}
 
static void line(const struct vertex *p, int n, double y)
{
    static double *xs;
    static int max_x;
    int num_x = 0;
    int i;
 
    for (i = 1; i < n; i++) {
        const struct vertex *p0 = &p[i - 1];
        const struct vertex *p1 = &p[i];
        const struct vertex *tmp;
        double x;
 
        if (p0->y == p1->y)
            continue;
 
        if (p0->y > p1->y)
            tmp = p0, p0 = p1, p1 = tmp;
 
        if (p0->y > y)
            continue;
 
        if (p1->y <= y)
            continue;
 
        x = p1->x * (y - p0->y) + p0->x * (p1->y - y);
        x /= p1->y - p0->y;
 
        if (num_x >= max_x) {
            max_x += 20;
            xs = G_realloc(xs, max_x * sizeof(double));
        }
 
        xs[num_x++] = x;
    }
 
    qsort(xs, num_x, sizeof(double), cmp_double);
 
    for (i = 0; i + 1 < num_x; i += 2)
        fill(xs[i], xs[i + 1], y);
}
 
static void poly(const struct vertex *p, int n)
{
    double y0, y1, y;
    int i;
 
    if (n < 3)
        return;
 
    y0 = y1 = p[0].y;
 
    for (i = 1; i < n; i++) {
        if (y0 > p[i].y)
            y0 = p[i].y;
 
        if (y1 < p[i].y)
            y1 = p[i].y;
    }
 
    if (y0 > png.clip_bot || y1 < png.clip_top)
        return;
 
    if (y0 < png.clip_top)
        y0 = png.clip_top;
 
    if (y1 > png.clip_bot)
        y1 = png.clip_bot;
 
    for (y = floor(y0 + 0.5) + 0.5; y < y1; y++)
        line(p, n, y);
}
 
/*!
   \brief Draw polygon
 */
void png_polygon(struct path *p)
{
    if (p->vertices[p->count - 1].mode != P_CLOSE)
        path_close(p);
 
    poly(p->vertices, p->count);
 
    png.modified = 1;
}