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1 #include "config.h"
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2 #include <string.h>
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3 #include <assert.h>
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4 #include "polyfill.h"
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5 #include "fixed.h"
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6 #include "gbasys.h"
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7
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8 static void fill_scanline(int y, int x0, int x1, uint16_t color);
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9
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10 void draw_poly(int num, const pvec3 *verts, uint16_t color)
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11 {
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12 int i, topidx = 0, botidx = 0;
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13 int lidx[2], ridx[2];
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14 int32_t y, topy, boty;
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15 int32_t ldy, rdy, ldxdy, rdxdy;
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16 int32_t lx, rx;
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17 int start, end;
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18
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19 topy = boty = verts[0].y;
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20 for(i=1; i<num; i++) {
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21 int32_t y = verts[i].y;
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22 if(y < topy) {
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23 topy = y;
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24 topidx = i;
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25 }
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26 if(y > boty) {
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27 boty = y;
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28 botidx = i;
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29 }
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30 }
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31
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32 lidx[0] = ridx[0] = topidx;
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33 lidx[1] = topidx ? topidx - 1 : num - 1;
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34 ridx[1] = (topidx + 1) % num;
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35
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36 if(verts[ridx[1]].x < verts[lidx[1]].x) {
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37 return; /* backface (CCW) */
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38 }
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39
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40 lx = rx = verts[lidx[0]].x;
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41
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42 /* TODO handle ldy == 0 or rdy == 0 */
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43 ldy = verts[lidx[1]].y - verts[lidx[0]].y;
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44 ldxdy = x16div(verts[lidx[1]].x - lx, ldy);
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45
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46 rdy = verts[ridx[1]].y - verts[ridx[0]].y;
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47 rdxdy = x16div(verts[ridx[1]].x - rx, rdy);
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48
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49 start = topy >> 16;
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50 end = boty >> 16;
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51
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52 if(end >= HEIGHT) end = HEIGHT - 1;
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53
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54 y = topy;
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55 for(i=start; i<end; i++) {
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56 unsigned short x0, x1;
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57
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58 x0 = lx < 0 ? 0 : (lx >> 16);
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59 x1 = (rx >> 16) >= WIDTH ? WIDTH - 1 : (rx >> 16);
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60
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61 if(i >= 0 && x1 > x0) {
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62 fill_scanline(i, x0, x1, color);
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63 }
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64
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65 if(y >= verts[lidx[1]].y) {
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66 lidx[0] = lidx[1];
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67 lidx[1] = lidx[1] ? lidx[1] - 1 : num - 1;
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68 ldy = verts[lidx[1]].y - verts[lidx[0]].y;
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69 if(ldy < 0) {
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70 break;
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71 }
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72 ldxdy = x16div(verts[lidx[1]].x - lx, ldy);
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73 }
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74 if(y >= verts[ridx[1]].y) {
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75 ridx[0] = ridx[1];
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76 ridx[1] = (ridx[1] + 1) % num;
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77 rdy = verts[ridx[1]].y - verts[ridx[0]].y;
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78 if(rdy < 0) {
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79 break;
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80 }
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81 rdxdy = x16div(verts[ridx[1]].x - rx, rdy);
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82 }
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83
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84 lx += ldxdy;
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85 rx += rdxdy;
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86 y += 65536;
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87 }
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88 }
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89
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90 static void fill_scanline(int y, int x0, int x1, uint16_t color)
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91 {
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92 int i;
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93 uint16_t *pixels = (uint16_t*)back_buffer->pixels + y * WIDTH + x0;
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94
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95 for(i=x0; i<x1; i++) {
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96 *pixels++ = color;
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97 }
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98 }
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