Lesson 6 of 10 · Ray marching in GLSL
The floor
A plane + min(). Two shapes share one scene.
A scene with one object is a lonely planet. To add more, you union SDFs with min(): the distance to the nearest thing is the smaller of the two. Sphere or floor, whichever is closer to the ray wins.
The floor is the cheapest SDF on Earth: p.y+1.0 is the vertical distance to a horizontal plane. Union it with the sphere and suddenly there is ground to stand on.
min(a, b) = union
min of two distances returns the nearest object. It is the union operator: it joins shapes into one scene. Later you will meet max for cuts and smin for soft blends.Change
p.y+1.0 to p.y+0.6 and the floor rises, the sphere seems to float. The first slider changes the radius (sph=length(p)-1.0).The code
precision highp float;
float map(vec3 p){
float sph=length(p)-1.0;
float flo=p.y+1.0;
return min(sph, flo);
}
vec3 nrm(vec3 p){
vec2 e=vec2(0.001,0.0);
return normalize(vec3(
map(p+e.xyy)-map(p-e.xyy),
map(p+e.yxy)-map(p-e.yxy),
map(p+e.yyx)-map(p-e.yyx)));
}
void main(){
vec2 uv=(gl_FragCoord.xy*2.0-R)/R.y;
vec3 ro=vec3(0.0,0.0,3.0);
vec3 rd=normalize(vec3(uv,-1.5));
float t=0.0;
float hit=0.0;
for(int i=0;i<64;i++){
vec3 pos=ro+rd*t;
float d=map(pos);
if(d<0.001){ hit=1.0; break; }
t+=d;
if(t>20.0) break;
}
vec3 pos=ro+rd*t;
vec3 n=nrm(pos);
vec3 lightDir=normalize(vec3(0.8,0.7,0.6));
float diff=max(dot(n,lightDir),0.0);
vec3 lit=vec3(0.85,0.55,0.35)*(diff*0.9+0.12);
vec3 sky=mix(vec3(0.05,0.06,0.12), vec3(0.16,0.22,0.42), uv.y*0.5+0.5);
float fog=1.0-exp(-t*0.08);
vec3 col=mix(lit, sky, fog);
col=mix(sky, col, hit);
gl_FragColor=vec4(col,1.0);
}