feat: add bump mapping to terrain for rougher, less smooth shading

shaders/simple.frag

@@ -9,15 +9,19 @@ void main() {
     // ambient component
     float ambientStrength = 0.1;
     vec3 ambient = ambientStrength * vColor.rgb;
-    // diffuse component (Lambert)
-    float lambert = max(0.0, dot(normalize(vNormal), -lightDirection));
+    // bump mapping perturbation
+    float bumpStrength = 0.2;
+    float nVal = fract(sin(dot(vNormal.xy, vec2(12.9898, 78.233))) * 43758.5453);
+    vec3 bumpNormal = normalize(vNormal + bumpStrength * (nVal - 0.5));
+    // diffuse component (Lambert) with bump
+    float lambert = max(0.0, dot(normalize(bumpNormal), -lightDirection));
     vec3 diffuse = vColor.rgb * lambert;
     // combine ambient and diffuse
     vec3 result = ambient + diffuse;
     // specular component (Phong)
     float shininess = 32.0;
     vec3 viewDir     = vec3(0.0, 0.0, 1.0);
-    vec3 reflectDir  = reflect(-lightDirection, normalize(vNormal));
+    vec3 reflectDir  = reflect(-lightDirection, bumpNormal);
     float spec       = pow(max(dot(reflectDir, viewDir), 0.0), shininess);
     float specStrength = 0.5;
     vec3 specular    = specStrength * spec * vec3(1.0);