Dogcows Code - chaz/rasterize/blob - tri.h

   1
   2 /*
   3  * CS5600 University of Utah
   4  * Charles McGarvey
   5  * mcgarvey@eng.utah.edu
   6  */
   7
   8 #ifndef _TRI_H_
   9 #define _TRI_H_
  10
  11 #include "aabb.h"
  12 #include "mat.h"
  13 #include "vert.h"
  14
  15
  16 /*
  17  * A triangle is a polygon of three vertices.
  18  */
  19 struct tri
  20 {
  21     vert_t a;
  22     vert_t b;
  23     vert_t c;
  24 };
  25 typedef struct tri tri_t;
  26
  27 /*
  28  * Initialize a triangle.
  29  */
  30 INLINE_MAYBE
  31 void tri_init(tri_t* t, vert_t a, vert_t b, vert_t c)
  32 {
  33     t->a = a;
  34     t->b = b;
  35     t->c = c;
  36 }
  37
  38
  39 /*
  40  * Create a new triangle.
  41  */
  42 INLINE_MAYBE
  43 tri_t tri_new(vert_t a, vert_t b, vert_t c)
  44 {
  45     tri_t t;
  46     tri_init(&t, a, b, c);
  47     return t;
  48 }
  49
  50 #define TRI_ZERO tri_new(VERT_ZERO, VERT_ZERO, VERT_ZERO)
  51
  52
  53 /*
  54  * Create a new triangle on the heap.
  55  */
  56 INLINE_MAYBE
  57 tri_t* tri_alloc(vert_t a, vert_t b, vert_t c)
  58 {
  59     tri_t* t = (tri_t*)mem_alloc(sizeof(tri_t));
  60     tri_init(t, a, b, c);
  61     return t;
  62 }
  63
  64
  65 /*
  66  * Apply a transformation matrix to alter the triangle geometry.
  67  */
  68 INLINE_MAYBE
  69 tri_t tri_transform(tri_t t, mat_t m)
  70 {
  71     t.a.v = mat_apply(m, t.a.v);
  72     t.b.v = mat_apply(m, t.b.v);
  73     t.c.v = mat_apply(m, t.c.v);
  74     return t;
  75 }
  76
  77 /*
  78  * Perform a homogeneous divide on the geometry.
  79  */
  80 INLINE_MAYBE
  81 tri_t tri_homodiv(tri_t t)
  82 {
  83     t.a.v = vec_homodiv(t.a.v);
  84     t.b.v = vec_homodiv(t.b.v);
  85     t.c.v = vec_homodiv(t.c.v);
  86     return t;
  87 }
  88
  89
  90 /*
  91  * Calculate a normal vector.
  92  */
  93 INLINE_MAYBE
  94 vec_t tri_normal(tri_t t)
  95 {
  96     return vec_cross(vec_sub(t.b.v, t.a.v), vec_sub(t.c.v, t.a.v));
  97 }
  98
  99
 100 /*
 101  * Calculate the AABB for the triangle.
 102  */
 103 INLINE_MAYBE
 104 aabb_t tri_aabb(tri_t t)
 105 {
 106     aabb_t b;
 107     b.min = vec_new(scal_min2(t.a.v.x, t.b.v.x, t.c.v.x),
 108                     scal_min2(t.a.v.y, t.b.v.y, t.c.v.y),
 109                     scal_min2(t.a.v.z, t.b.v.z, t.c.v.z));
 110     b.max = vec_new(scal_max2(t.a.v.x, t.b.v.x, t.c.v.x),
 111                     scal_max2(t.a.v.y, t.b.v.y, t.c.v.y),
 112                     scal_max2(t.a.v.z, t.b.v.z, t.c.v.z));
 113     return b;
 114 }
 115
 116
 117 /*
 118  * Get the barycentric coordinates of a vector against a triangle.  The
 119  * returned coordinates will be a linear combination, but they may not
 120  * actually be barycentric coordinates.  Use the function vec_is_barycentric
 121  * to check if they really are barycentric coordinates, meaning the point
 122  * vector v is inside the triangle, ignoring the Z components.
 123  */
 124 INLINE_MAYBE
 125 bool tri_barycentric(tri_t t, scal_t* b, vec_t v)
 126 {
 127     scal_t denom = (t.b.v.y - t.c.v.y) * (t.a.v.x - t.c.v.x) + (t.c.v.x - t.b.v.x) * (t.a.v.y - t.c.v.y);
 128     b[0] = ((t.b.v.y - t.c.v.y) * (v.x - t.c.v.x) + (t.c.v.x - t.b.v.x) * (v.y - t.c.v.y)) / denom;
 129     b[1] = ((t.c.v.y - t.a.v.y) * (v.x - t.c.v.x) + (t.a.v.x - t.c.v.x) * (v.y - t.c.v.y)) / denom;
 130     b[2] = S(1.0) - b[0] - b[1];
 131     if (S(0.0) <= b[0] && b[0] <= S(1.0) &&
 132         S(0.0) <= b[1] && b[1] <= S(1.0) &&
 133         S(0.0) <= b[2] && b[2] <= S(1.0)) {
 134         return true;
 135     }
 136     return false;
 137 }
 138
 139
 140 /*
 141  * Get an interpolated z-value at the barycentric coordinates.
 142  */
 143 INLINE_MAYBE
 144 scal_t tri_z(tri_t t, scal_t b[3])
 145 {
 146     return t.a.v.z * b[0] + t.b.v.z * b[1] + t.c.v.z * b[2];
 147 }
 148
 149 /*
 150  * Find the midpoint of the triangle.
 151  */
 152 INLINE_MAYBE
 153 vec_t tri_midpoint(tri_t t)
 154 {
 155     return vec_new((t.a.v.x + t.b.v.x + t.c.v.x) * S(0.333),
 156                    (t.a.v.y + t.b.v.y + t.c.v.y) * S(0.333),
 157                    (t.a.v.z + t.b.v.z + t.c.v.z) * S(0.333));
 158 }
 159
 160 /*
 161  * Get the average color of the triangle.
 162  */
 163 INLINE_MAYBE
 164 color_t tri_color(tri_t t)
 165 {
 166     scal_t b[] = {S(0.333), S(0.333), S(0.333)};
 167     return color_interp2(t.a.c, t.b.c, t.c.c, b);
 168 }
 169
 170
 171 #endif // _TRI_H_
 172