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これがGPUの力!three.jsによる“リアルタイム”なレイトレーシング 〜宝石編〜 ref: http://qiita.com/gam0022/items/9875480d33e03fe2113c
// 3次正方行列の行列式をクラメルの公式で計算する
float det( vec3 a, vec3 b, vec3 c ) {
return (a.x * b.y * c.z)
+ (a.y * b.z * c.x)
+ (a.z * b.x * c.y)
- (a.x * b.z * c.y)
- (a.y * b.x * c.z)
- (a.z * b.y * c.x);
}
// ポリゴン(三角形)とレイ(半直線)の衝突判定する
void rayIntersectsTriangle( vec3 origin, vec3 ray, vec3 v0, vec3 v1, vec3 v2, inout Intersect nearest ) {
vec3 invRay = -ray;
vec3 edge1 = v1 - v0;
vec3 edge2 = v2 - v0;
float denominator = det( edge1, edge2, invRay );
if ( denominator == 0.0 ) return;
float invDenominator = 1.0 / denominator;
vec3 d = origin - v0;
float u = det( d, edge2, invRay ) * invDenominator;
if ( u < 0.0 || u > 1.0 ) return;
float v = det( edge1, d, invRay ) * invDenominator;
if ( v < 0.0 || u + v > 1.0 ) return;
float t = det( edge1, edge2, d ) * invDenominator;
if ( t < 0.0 || t > nearest.distance ) return;
nearest.isHit = true;
nearest.position = origin + ray * t;
nearest.distance = t;
nearest.normal = normalize( cross( edge1, edge2 ) ) * sign( invDenominator );
nearest.material = DIAMOND_MATERIAL;
nearest.isFront = invDenominator > 0.0;
}
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