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16
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1
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2 // written in the D programming language
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3
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4 module samples.Planet;
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5
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6 import chipmunkd.chipmunk;
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7
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8 import samples.ChipmunkDemo;
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9
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10 static cpSpace *space;
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11 static cpBody *planetBody;
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12
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13 static cpFloat gravityStrength = 5.0e6f;
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14
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15 static void
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16 update(int ticks)
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17 {
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18 int steps = 1;
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19 cpFloat dt = 1.0f/60.0f/cast(cpFloat)steps;
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20
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21 for(int i=0; i<steps; i++){
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22 cpSpaceStep(space, dt);
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23
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24 // Update the static body spin so that it looks like it's rotating.
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25 cpBodyUpdatePosition(planetBody, dt);
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26 }
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27 }
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28
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29 static void
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30 planetGravityVelocityFunc(cpBody *_body, cpVect gravity, cpFloat damping, cpFloat dt)
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31 {
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32 // Gravitational acceleration is proportional to the inverse square of
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33 // distance, and directed toward the origin. The central planet is assumed
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34 // to be massive enough that it affects the satellites but not vice versa.
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35 cpVect p = _body.p;
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36 cpFloat sqdist = cpvlengthsq(p);
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37 cpVect g = cpvmult(p, -gravityStrength / (sqdist * cpfsqrt(sqdist)));
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38
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39 cpBodyUpdateVelocity(_body, g, damping, dt);
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40 }
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41
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42 static cpVect
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43 rand_pos(cpFloat radius)
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44 {
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45 cpVect v;
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46 do {
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47 v = cpv(frand()*(640 - 2*radius) - (320 - radius), frand()*(480 - 2*radius) - (240 - radius));
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48 } while(cpvlength(v) < 85.0f);
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49
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50 return v;
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51 }
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52
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53 static void
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54 add_box()
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55 {
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56 const cpFloat size = 10.0f;
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57 const cpFloat mass = 1.0f;
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58
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59 cpVect verts[] = [
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60 cpv(-size,-size),
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61 cpv(-size, size),
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62 cpv( size, size),
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63 cpv( size,-size),
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64 ];
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65
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66 cpFloat radius = cpvlength(cpv(size, size));
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67
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68 cpBody *_body = cpSpaceAddBody(space, cpBodyNew(mass, cpMomentForPoly(mass, 4, verts.ptr, cpvzero)));
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69 _body.velocity_func = &planetGravityVelocityFunc;
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70 _body.p = rand_pos(radius);
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71
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72 // Set the box's velocity to put it into a circular orbit from its
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73 // starting position.
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74 cpFloat r = cpvlength(_body.p);
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75 cpFloat v = cpfsqrt(gravityStrength / r) / r;
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76 _body.v = cpvmult(cpvperp(_body.p), v);
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77
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78 // Set the box's angular velocity to match its orbital period and
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79 // align its initial angle with its position.
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80 _body.w = v;
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81 cpBodySetAngle(_body, cpfatan2(_body.p.y, _body.p.x));
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82
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83 cpShape *shape = cpSpaceAddShape(space, cpPolyShapeNew(_body, 4, verts.ptr, cpvzero));
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84 shape.e = 0.0f; shape.u = 0.7f;
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85 }
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86
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87 static cpSpace *
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88 init()
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89 {
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90 planetBody = cpBodyNew(INFINITY, INFINITY);
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91 planetBody.w = 0.2f;
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92
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93 cpResetShapeIdCounter();
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94
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95 space = cpSpaceNew();
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96 cpSpaceResizeActiveHash(space, 30.0f, 10000);
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97 space.iterations = 20;
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98
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99 for(int i=0; i<30; i++)
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100 add_box();
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101
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102 cpShape *shape = cpSpaceAddShape(space, cpCircleShapeNew(planetBody, 70.0f, cpvzero));
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103 shape.e = 1.0f; shape.u = 1.0f;
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104 shape.layers = NOT_GRABABLE_MASK;
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105
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106 return space;
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107 }
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108
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109 static void
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110 destroy()
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111 {
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112 cpBodyFree(planetBody);
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113 cpSpaceFreeChildren(space);
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114 cpSpaceFree(space);
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115 }
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116
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117 chipmunkDemo Planet = {
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118 "Planet",
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119 null,
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120 &init,
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121 &update,
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122 &destroy,
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123 };
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