Learn more about Russian war crimes in Ukraine.

Generating a normal map in WebGL

Previously I’ve shown some examples of normal maps loaded from a static file. Here, I’m generating the normal map dynamically. The normal map is of a cone seen from the top. Here’s the fragment shader:

precision mediump float;
mat4 rotateZ(float ang) {
    return mat4(
void main(void) {
  vec2 coord = vec2(gl_FragCoord) - vec2(256., 256.);
  float ang = atan(coord.y, coord.x);
  vec4 normal = rotateZ(ang) * normalize(vec4(3.0, 0.0, 1.0, 0.0));
  gl_FragColor = vec4(vec3((normal+1.) * 0.5), 1.0);

One use of dynamically generated normal maps is to simulate water. I would generate a normal map to simulate the ripples on the water surface. I can then use this normal map to refract light. These simulated ripples would change every frame. It’s prohibitive to upload a new texture for every frame, so we really want to calculate those ripples in the fragment shader. I’ll show a generated ripply normal map in future.

The fragment shader makes use of a rotateZ function. I’ll publish a blog post containing all these standard transformation functions; it’s pretty silly that they’re not in the GLSL standard library.

The fragment shader also makes use of some functions to convert between normals and colors. I’ll also post those in future.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

It’s only $19, and you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

More by Jim

Tagged . All content copyright James Fisher 2017. This post is not associated with my employer. Found an error? Edit this page.