GLSL define does calculation or replaces text?

Question

For something relatively expensive but constant such as `pow()` with pre-runtime user specified constants, can a `define` be used to reduce the runtime calculation? Or would each appearance of `define` just be replaced with what it defines? For example, is there any benefit to this: ``` #define MENGER_ITER 3 #define MENGER_ITER_POW pow(3.0, -float(MENGER_ITER)) // ...other code return (length(max(abs(vec3(x, y, z))-1.0, 0.0))-0.25)*MENGER_ITER_POW; // ...other code ``` As opposed to this: ``` // ...other code return (length(max(abs(vec3(x, y, z))-1.0, 0.0))-0.25)*pow(3.0, -float(MENGER_ITER)); // ...other code ```

Accepted Answer

`#define` just does a text substitution

For your case it's no different than

```
shaderSource = shaderSource.replace(/MENGER_ITER_POW/g, "pow(3.0, -float(MENGER_ITER))");
shaderSource = shaderSource.replace(/MENGER_ITER/g, "3");
gl.shaderSource(someShader, shaderSource);
```

It's very similar to the C/C++ preprocessor

The benefit is it makes your code more readable?

GLSL define does calculation or replaces text?

Solution

Problem