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1 #include <stdio.h>
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2 #include <stdlib.h>
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3 #include <stdarg.h>
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4 #include <assert.h>
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5 #include <GL/glut.h>
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6 #include <vmath/vmath.h>
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7 #include <drawtext.h>
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8
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9 bool init();
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10 void display();
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11 void draw_grid();
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12 void draw_frustum();
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13 void draw_label(const Vector2 &pos, const char *fmt, ...);
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14 void reshape(int x, int y);
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15 void keyb(unsigned char key, int x, int y);
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16 void keyb_up(unsigned char key, int x, int y);
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17 void mouse(int bn, int st, int x, int y);
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18 void motion(int x, int y);
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19 Vector2 screen_to_world(int x, int y);
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20 Vector2 project(const Vector2 &v);
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21 Vector2 unproject(const Vector2 &v);
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22 float calc_proj_dist(float fov);
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23
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24 int win_xsz, win_ysz;
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25 float aspect;
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26
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27 Matrix4x4 proj;
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28 float proj_offset;
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29 Vector2 cur_point;
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30 bool cur_point_valid;
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31
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32 float proj_near = 0.5, proj_far = 50.0;
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33 float proj_vfov = 60.0;
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34
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35 bool keystate[256];
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36 bool bnstate[16];
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37 int prev_x, prev_y;
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38 unsigned int modkeys;
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39
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40 dtx_font *font;
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41 float pan[2] = {0, 0.85}, zoom = 0.3;
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42 float snap_dist = 0.25;
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43
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44 int main(int argc, char **argv)
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45 {
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46 glutInit(&argc, argv);
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47 glutInitWindowSize(1024, 768);
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48 glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_MULTISAMPLE);
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49 glutCreateWindow("Interactive projection diagram");
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50
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51 glutDisplayFunc(display);
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52 glutReshapeFunc(reshape);
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53 glutKeyboardFunc(keyb);
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54 glutKeyboardUpFunc(keyb_up);
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55 glutMouseFunc(mouse);
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56 glutMotionFunc(motion);
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57
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58 if(!init()) {
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59 return 1;
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60 }
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61
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62 glutMainLoop();
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63 return 0;
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64 }
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65
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66 bool init()
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67 {
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68 if(!(font = dtx_open_font("data/font.ttf", 16))) {
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69 fprintf(stderr, "failed to open font\n");
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70 return false;
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71 }
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72
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73 glEnable(GL_MULTISAMPLE);
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74 proj.set_perspective(DEG_TO_RAD(proj_vfov), 1, 1.0, 50.0);
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75 proj.translate(Vector3(proj_offset, 0, 0));
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76 return true;
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77 }
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78
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79 void display()
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80 {
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81 glClear(GL_COLOR_BUFFER_BIT);
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82
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83 glMatrixMode(GL_MODELVIEW);
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84 glLoadIdentity();
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85 glTranslatef(-pan[0], -pan[1], 0);
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86 glScalef(zoom, zoom, zoom);
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87
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88 draw_grid();
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89
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90 draw_frustum();
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91
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92 if(cur_point_valid) {
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93 Vector2 ppt = project(cur_point);
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94
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95 glPointSize(7.0);
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96 glBegin(GL_POINTS);
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97 glColor3f(0.2, 1, 0.2);
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98 glVertex2f(cur_point.x, cur_point.y);
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99 glColor3f(0.7, 0.2, 0.2);
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100 glVertex2f(ppt.x, ppt.y);
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101 glEnd();
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102
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103 glEnable(GL_LINE_STIPPLE);
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104 glLineStipple(4, 0xe0e0);
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105
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106 glBegin(GL_LINES);
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107 glColor3f(0.2, 0.5, 0.2);
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108 glVertex2f(cur_point.x, cur_point.y);
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109 glColor3f(0.5, 0.2, 0.2);
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110 glVertex2f(ppt.x, ppt.y);
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111 glEnd();
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112 glDisable(GL_LINE_STIPPLE);
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113
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114 glColor3f(0.2, 0.5, 0.2);
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115 draw_label(cur_point, "(%.2f, %.2f)", cur_point.x, cur_point.y);
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116 glColor3f(0.5, 0.2, 0.2);
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117 draw_label(ppt, "(%.2f, %.2f)", ppt.x, ppt.y);
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118 }
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119
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120 glutSwapBuffers();
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121 assert(glGetError() == GL_NO_ERROR);
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122 }
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123
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124 #define LINE(x0, y0, x1, y1) (glVertex2f(x0, y0), glVertex2f(x1, y1))
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125
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126 void draw_grid()
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127 {
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128 float ymin = -10;
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129 float ymax = 10;
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130 float xmin = -10;
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131 float xmax = 10;
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132 float ticksz = 0.015 / zoom;
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133
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134 glBegin(GL_LINES);
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135 glColor3f(1, 1, 1);
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136 LINE(0, -10, 0, 10);
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137 LINE(-10, 0, 10, 0);
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138
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139 for(int i=1; i<11; i++) {
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140 for(int j=0; j<2; j++) {
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141 float x = 10.0 * (float)i / 10.0 * (j ? -1.0 : 1.0);
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142
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143 glColor3f(0.15, 0.15, 0.15);
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144 LINE(x, ymin, x, ymax);
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145 LINE(xmin, x, xmax, x);
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146
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147 glColor3f(0.4, 0.4, 0.4);
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148 LINE(x, -ticksz, x, ticksz);
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149 LINE(-ticksz, x, ticksz, x);
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150 }
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151 }
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152 glEnd();
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153 }
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154
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155 void draw_frustum()
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156 {
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157 Vector2 left[2], right[2];
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158
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159 glBegin(GL_LINES);
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160 glColor3f(0.2, 0.4, 0.8);
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161
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162 right[0] = unproject(Vector2(1, 0));
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163 right[1] = unproject(Vector2(1, 1));
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164 LINE(right[0].x, right[0].y, right[1].x, right[1].y);
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165
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166 left[0] = unproject(Vector2(-1, 0));
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167 left[1] = unproject(Vector2(-1, 1));
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168 LINE(left[0].x, left[0].y, left[1].x, left[1].y);
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169
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170 float dist = calc_proj_dist(proj_vfov);
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171 LINE(-1, dist, 1, dist);
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172 glEnd();
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173
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174 /* find the points where the frustum lines hit zero */
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175 glEnable(GL_LINE_STIPPLE);
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176 glLineStipple(3, 0x0101);
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177
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178 glBegin(GL_LINES);
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179 for(int i=0; i<2; i++) {
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180 Vector2 *v = i ? left : right;
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181 float t = -v[1].y / (v[0].y - v[1].y);
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182 float x = v[1].x + (v[0].x - v[1].x) * t;
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183 LINE(v[0].x, v[0].y, x, 0);
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184 }
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185 glEnd();
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186 glDisable(GL_LINE_STIPPLE);
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187 }
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188
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189 void draw_label(const Vector2 &pos, const char *fmt, ...)
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190 {
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191 static char buf[512];
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192 va_list ap;
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193
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194 va_start(ap, fmt);
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195 vsnprintf(buf, sizeof buf - 1, fmt, ap);
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196 va_end(ap);
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197
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198 glPushMatrix();
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199 glTranslatef(pos.x + 0.01, pos.y + 0.01, 0);
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200 float s = 2.0 / (win_ysz * zoom);
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201 glScalef(s, s, s);
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202
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203 dtx_string(buf);
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204
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205 glPopMatrix();
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206 }
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207
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208 void reshape(int x, int y)
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209 {
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210 win_xsz = x;
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211 win_ysz = y;
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212 aspect = (float)x / (float)y;
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213
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214 glViewport(0, 0, x, y);
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215
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216 glMatrixMode(GL_PROJECTION);
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217 glLoadIdentity();
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218 glScalef(1.0 / aspect, 1.0, 1.0);
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219 }
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220
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221 void keyb(unsigned char key, int x, int y)
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222 {
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223 keystate[key] = 1;
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224 modkeys = glutGetModifiers();
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225
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226 switch(key) {
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227 case 27:
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228 exit(0);
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229 }
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230 }
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231
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232 void keyb_up(unsigned char key, int x, int y)
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233 {
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234 keystate[key] = 0;
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235 modkeys = glutGetModifiers();
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236 }
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237
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238 void mouse(int bn, int st, int x, int y)
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239 {
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240 bnstate[bn - GLUT_LEFT_BUTTON] = st == GLUT_DOWN;
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241 prev_x = x;
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242 prev_y = y;
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243 modkeys = glutGetModifiers();
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244
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245 if(bn == GLUT_LEFT_BUTTON && st == GLUT_DOWN) {
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246 cur_point = screen_to_world(x, y);
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247 cur_point_valid = true;
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248 glutPostRedisplay();
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249 }
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250 }
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251
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252 void motion(int x, int y)
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253 {
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254 float dx = 2.0 * aspect * (x - prev_x) / (float)win_xsz;
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255 float dy = 2.0 * (y - prev_y) / (float)win_ysz;
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256 prev_x = x;
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257 prev_y = y;
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258
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259 if(bnstate[0]) {
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260 cur_point = screen_to_world(x, y);
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261 if(keystate['s'] || keystate['S']) {
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262 cur_point.x = round(cur_point.x / snap_dist) * snap_dist;
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263 cur_point.y = round(cur_point.y / snap_dist) * snap_dist;
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264 }
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265 glutPostRedisplay();
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266 }
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267 if(bnstate[1]) {
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268 pan[0] -= dx;
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269 pan[1] += dy;
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270
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271 glutPostRedisplay();
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272 }
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273 if(bnstate[2]) {
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274 zoom += dy;
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275
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276 if(zoom < 1e-4) zoom = 1e-4;
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277 glutPostRedisplay();
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278 }
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279 }
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280
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281 Vector2 screen_to_world(int px, int py)
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282 {
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283 /* canonical [-1, 1] system */
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284 float x = aspect * ((float)px * 2.0 / (float)win_xsz - 1.0);
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285 float y = (float)(win_ysz - py) * 2.0 / (float)win_ysz - 1.0;
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286
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287 /* account for pan & zoom */
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288 x = (x + pan[0]) / zoom;
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289 y = (y + pan[1]) / zoom;
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290
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291 return Vector2(x, y);
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292 }
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293
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294 Vector2 project(const Vector2 &v)
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295 {
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296 Vector4 ppt = Vector4(v.x, 0, -v.y, 1).transformed(proj);
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297 return Vector2(ppt.x / ppt.w, calc_proj_dist(proj_vfov));
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298 }
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299
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300 Vector2 unproject(const Vector2 &v)
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301 {
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302 Vector4 v4 = Vector4(v.x, 0.0, v.y, 1.0);
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303 Matrix4x4 inv_proj = proj.inverse();
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304
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305 Vector4 res4 = v4.transformed(inv_proj);
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306 return Vector2(res4.x / res4.w, -res4.z / res4.w);
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307 }
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308
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309 float calc_proj_dist(float fov)
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310 {
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311 return 1.0 / tan(DEG_TO_RAD(fov) / 2.0);
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312 }
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