wgpu: [glsl-out] Incorrect rounding for max-float constant expression

? That does not pass glslangValidator validation:

This is surprising to me. The GLSL spec (3.20.6) says that a constant expression can be:

A built-in function call whose arguments are all constant expressions, with the exception of the texture lookup functions.

This seems to date all the way back to GLSL ES 1.0.

In a webgl2 shader, it seems like indeed 3.4028235e38 != 3.4028234663852886e38 with precision highp float: https://fornwall.net/webgl2-float-comparison (at least on all browser and os setups I’ve tested with)

As said above, this is in contrast to treating the numbers are 32-bit floats, for instance in rust: assert_eq!(3.4028235e38_f32, 3.4028234663852886e38_f32);.

So the effective behaviour is like the shader uses f64 in computations:

let value_from_texture = 3.4028235e38_f32 as f64;
let f32max: f64 = 3.4028235e38_f32;

which causes value_from_texture >= f32max to be false.

Using f64 literals would indeed solve this problem. Are there any potential drawbacks? Let’s create a PR to raise visibility and perhaps get more eyes on it (I can do it later today).