diff options
Diffstat (limited to 'engines')
| -rw-r--r-- | engines/bladerunner/fog.cpp | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/engines/bladerunner/fog.cpp b/engines/bladerunner/fog.cpp index 4856f1d3b3..e6b603702e 100644 --- a/engines/bladerunner/fog.cpp +++ b/engines/bladerunner/fog.cpp @@ -123,18 +123,25 @@ void FogSphere::read(Common::ReadStream *stream, int frameCount) { void FogSphere::calculateCoeficient(Vector3 position, Vector3 viewPosition, float *coeficient) { *coeficient = 0.0f; - // ray - sphere intersection, where sphere center is always at 0, 0, 0 as everything else tranformed by the fog matrix + // Ray - sphere intersection, where sphere center is always at 0, 0, 0 as everything else tranformed by the fog matrix. + // Quadratic formula can and was simplified becasue rayDirection is normalized and hence a = 1. + // Explained on wikipedia https://en.wikipedia.org/wiki/Line%E2%80%93sphere_intersection + + // There is also alternative approach which will end-up with this formula where plane is created from ray origin, ray destination + // and sphere center, then there is only need to solve two right triangles. + // Explained in book Andrew S. Glassner (1995), Graphics Gems I (p. 388-389) + Vector3 rayOrigin = _matrix * position; Vector3 rayDestination = _matrix * viewPosition; Vector3 rayDirection = (rayDestination - rayOrigin).normalize(); float b = Vector3::dot(rayDirection, rayOrigin); float c = Vector3::dot(rayOrigin, rayOrigin) - (_radius * _radius); - float t = b * b - c; + float d = b * b - c; - if (t >= 0.0f) { // there is an interstection between ray and the sphere - Vector3 intersection1 = rayOrigin + (-b - sqrt(t)) * rayDirection; - Vector3 intersection2 = rayOrigin + (-b + sqrt(t)) * rayDirection; + if (d >= 0.0f) { // there is an interstection between ray and the sphere + Vector3 intersection1 = rayOrigin + (-b - sqrt(d)) * rayDirection; + Vector3 intersection2 = rayOrigin + (-b + sqrt(d)) * rayDirection; Vector3 intersection1World = _inverted * intersection1; Vector3 intersection2World = _inverted * intersection2; |