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1 #include "config.h"
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2 #include <string.h>
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3 #include "polyfill.h"
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4 #include "fixed.h"
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5 #include "gbasys.h"
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6
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7 static void fill_scanline(int y, int x0, int x1, uint16_t color);
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8
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9 void draw_poly(int num, const pvec3 *verts, uint16_t color)
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10 {
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11 int i, topidx = 0, botidx = 0;
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12 int lidx[2], ridx[2];
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13 int32_t y, topy, boty;
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14 int32_t ldy, rdy, ldxdy, rdxdy;
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15 int32_t lx, rx;
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16 int start, end;
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17
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18 topy = boty = verts[0].y;
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19 for(i=1; i<num; i++) {
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20 int32_t y = verts[i].y;
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21 if(y < topy) {
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22 topy = y;
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23 topidx = i;
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24 }
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25 if(y > boty) {
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26 boty = y;
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27 botidx = i;
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28 }
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29 }
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30
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31 lidx[0] = ridx[0] = topidx;
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32 lidx[1] = topidx ? topidx - 1 : num - 1;
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33 ridx[1] = (topidx + 1) % num;
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34
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35 if(ridx[1] < lidx[1]) {
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36 return; /* backface (CCW) */
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37 }
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38
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39 lx = rx = verts[lidx[0]].x;
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40
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41 ldy = verts[lidx[1]].y - verts[lidx[0]].y;
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42 ldxdy = x16div(verts[lidx[1]].x - lx, ldy);
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43
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44 rdy = verts[ridx[1]].y - verts[ridx[1]].y;
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45 rdxdy = x16div(verts[ridx[1]].x - rx, rdy);
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46
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47 start = topy >> 16;
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48 end = boty >> 16;
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49
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50 y = topy;
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51 for(i=start; i<end; i++) {
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52 unsigned short x0, x1;
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53
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54 x0 = lx < 0 ? 0 : (lx >> 16);
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55 x1 = rx >= WIDTH ? WIDTH - 1 : (rx >> 16);
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56
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57 fill_scanline(i, x0, x1, color);
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58
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59 if(y >= verts[lidx[1]].y) {
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60 lidx[0] = lidx[1];
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61 lidx[1] = lidx[1] ? lidx[1] - 1 : num - 1;
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62 ldy = verts[lidx[1]].y - verts[lidx[0]].y;
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63 if(ldy < 0) {
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64 break;
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65 }
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66 ldxdy = x16div(verts[lidx[1]].x - lx, ldy);
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67 }
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68 if(y >= verts[ridx[1]].y) {
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69 ridx[0] = ridx[1];
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70 ridx[1] = (ridx[1] + 1) % num;
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71 rdy = verts[ridx[1]].y - verts[ridx[0]].y;
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72 if(rdy < 0) {
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73 break;
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74 }
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75 rdxdy = x16div(verts[ridx[1]].x - rx, rdy);
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76 }
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77
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78 lx += ldxdy;
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79 rx += rdxdy;
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80 }
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81 }
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82
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83 static void fill_scanline(int y, int x0, int x1, uint16_t color)
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84 {
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85 int i;
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86 uint16_t *pixels = (uint16_t*)back_buffer->pixels + y * WIDTH + x0;
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87
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88 for(i=x0; i<x1; i++) {
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89 *pixels++ = color;
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90 }
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91 }
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