+ if(!isect_plane(ro, rd, vec4(0.0, 1.0, 0.0, -1.0), hit)) {
+ return false;
+ }
+
+ float d = max(abs(hit.pos.x), abs(hit.pos.z));
+ if(d >= rad) return false;
+
+ return true;
+}
+
+bool isect_plane(in vec3 ro, in vec3 rd, in vec4 plane, out HitPoint hit)
+{
+ float ndotrd = dot(rd, plane.xyz);
+
+ if(abs(ndotrd) < 1e-6) {
+ return false;
+ }
+
+ vec3 pp = plane.xyz * plane.w;
+ vec3 pdir = pp - ro;
+ float t = dot(pdir, plane.xyz) / ndotrd;
+
+ hit.dist = t;
+ hit.pos = ro + rd * t;
+ hit.norm = plane.xyz;
+ hit.surfpos = hit.pos.xz; /* XXX */
+ return true;
+}
+
+bool isect_sphere(in vec3 ro, in vec3 rd, in vec3 pos, float rad, out HitPoint hit)
+{
+ float a = dot(rd, rd);
+ float b = dot(rd * 2.0, (ro - pos));
+ float c = dot(ro, ro) + dot(pos, pos) - 2.0 * dot(ro, pos) - rad * rad;
+
+ float d = b * b - 4.0 * a * c;
+ if(d < 1e-6) {
+ return false;
+ }
+
+ float t0 = (-b + sqrt(d)) / (2.0 * a);
+ float t1 = (-b - sqrt(d)) / (2.0 * a);
+
+ if(t0 < 0.0) t0 = t1;
+ if(t1 < 0.0) t1 = t0;
+ float t = min(t0, t1);
+
+ if(t < 1e-6) {
+ return false;
+ }