112 lines
2.8 KiB
C
112 lines
2.8 KiB
C
#include <emscripten.h>
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#include <string.h>
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typedef unsigned char Uint8;
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typedef unsigned short Uint16;
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typedef unsigned int Uint32;
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struct info {
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Uint16 width; // image width
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Uint16 height; // image height
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Uint16 polys; // total number of polygons to render
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};
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struct poly {
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Uint16 length; // offset to end of record in bytes
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Uint16 inners; // number of inner polygons
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Uint16 points; // number of points in polygon
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};
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struct point {
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float x;
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float y;
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};
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extern void last(float a, float b);
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extern void report(int a, int b);
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Uint32 readoff; // read position offset
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Uint8 check_cross(Uint32 x, Uint32 y, struct point *p1, struct point *p2) {
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return (
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((p1->y >= y) != (p2->y >= y)) &&
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(x < (p2->x - p1->x) * (y - p1->y) / (p2->y - p1->y) + p1->x)
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) ? 1 : 0;
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}
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Uint8 check_inside(Uint32 x, Uint32 y, unsigned char *p) {
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struct poly *poly = (struct poly *)(p + readoff);
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Uint32 nextpoly = readoff + poly->length;
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Uint8 side = 0; // 0=outside, 1=inside
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Uint8 psize = sizeof(struct point);
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// skip post header
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readoff += sizeof(struct poly);
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// save pointer to first point or last comparison
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struct point *pf = (struct point *)(p + readoff);
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struct point *p1 = pf;
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struct point *p2;
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// skip past first point
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readoff += psize;
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// read and check point pairs updating `side`
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for (Uint16 i=1; i<poly->points; i++) {
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p2 = (struct point *)(p + readoff);
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// increment read pointe
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readoff += psize;
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// check current/previous point crossing
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if (check_cross(x, y, p1, p2)) {
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side = 1 - side;
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}
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p1 = p2;
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}
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// check last/first point crossing
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if (check_cross(x, y, p1, pf)) {
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side = 1 - side;
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}
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// check inner polygons only if inside the outer polygon
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if (side)
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for (Uint16 i=0; i<poly->inners; i++) {
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// if inside an inner, then actually outside poly and term
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if (check_inside(x, y, p + readoff)) {
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side = 0;
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break;
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}
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}
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// update pointer to next polygon
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readoff = nextpoly;
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return side;
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}
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EMSCRIPTEN_KEEPALIVE
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Uint32 render(unsigned char *m, Uint32 i, Uint32 o) {
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struct info *info = (struct info *)(m + i);
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Uint32 impos;
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Uint8 inside;
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Uint32 maxpos = 0;
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Uint32 polypos = (sizeof (struct info)) + i;
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memset(m+o, 0, info->width * info->height);
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for (Uint32 x=0; x<info->width; x++) {
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for (Uint32 y=0; y<info->height; y++) {
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inside = 0;
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impos = y + (x * info->height);
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readoff = polypos;
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for (Uint32 p=0; p<info->polys; p++) {
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inside = inside | check_inside(x, y, m);
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}
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if (inside) (m + o)[impos] = 255;
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if (impos > maxpos) maxpos = impos;
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}
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}
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return maxpos;
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}
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