GLSL Ray-Sphere intersection bypassing precision issues
Many ray-sphere intersection implementations suffer from precision issues when the sphere is too small or the ray is too close, as described in this paper:
"Precision Improvements for Ray/Sphere Intersection" By: Eric Haines, Johannes Gunther, and Tomas Akenine-Moller https://link.springer.com/content/pdf/10.1007/978-1-4842-4427-2_7.pdf
This implementation uses the algorithm that bypasses those issues.
Intended for use with glslify.
// Add these lines:
#pragma glslify: Intersection = require(glsl-ray-sphere/intersection)
#pragma glslify: sphereIntersection = require(glsl-ray-sphere/rsi, Intersection=Intersection)
uniform vec3 ray; // normalized
uniform vec3 rayOrigin; // relative to the sphere
uniform float sphereRadius;
// Use it:
void main() {
Intersection inter = sphereIntersection(rayOrigin, ray, sphereRadius);
// number of hits in the forward direction:
int numberOfHitsInFront = inter.hits;
// is the ray inside?
bool isInside = inter.isInside;
// distances from ray origin are t0 and t1
// so get the points by:
vec3 first = rayOrigin + ray * inter.t0;
vec3 second = rayOrigin + ray * inter.t1;
}