Lesson 9 of 10 · Ray marching in GLSL
Material
Color by position + a sharp specular highlight.
So far everything was one flat color. A material decides the color at each hit point. Here we pull it from position with a cos, which cycles through colors as the height changes.
And we add the touch that sells realism: the specular, that bright dot where light bounces straight into the eye. It is the normal against the half-vector between light and camera, raised to a power: pow(..., 32.0). More power, smaller and harder highlight.
SpecularThe direct reflection of the light. When normal, light and view nearly align, the spot ignites. The power (
32.0) sets the size: high = metallic pinpoint, low = broad matte sheen.Raise the
32.0 in pow(..., 32.0) and the highlight tightens to a point. The second slider changes the color rhythm (pos.y*2.0).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(0.7, 0.9, 0.5));
float diff=max(dot(n,lightDir),0.0);
vec3 mat=0.5+0.5*cos(pos.y*2.0+vec3(0.0,2.0,4.0));
vec3 hv=normalize(lightDir+normalize(ro-pos));
float spec=pow(max(dot(n,hv),0.0), 32.0);
vec3 lit=mat*(diff*0.85+0.15)+vec3(1.0)*spec*0.7;
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);
}