Fragment shader doesn't support indexing uniform array with int variable.

[curvednebula]

Steps to reproduce

Bellow is the content of image_processor.frag:

#include <flutter/runtime_effect.glsl>

const int CURVE_SIZE = 512;

out vec4 fragColor;
uniform vec2 uSize;
uniform float curves[CURVE_SIZE * CURVES_NUM];
uniform sampler2D image;

void main() {
    vec2 iResolution = uSize;
    vec2 fragCoord = FlutterFragCoord();
    vec2 uv = fragCoord/iResolution.xy;
    vec3 rgb = texture(image, uv).xyz;

    int idx = 0;
    rgb.x = rgb.x * curves[0]; // change this line to rgb.x = rgb.x * curves[idx];

    fragColor = vec4(rgb, 1.0);
}

It works as expected. But if I change only a single:

rgb.x = rgb.x * curves[0]; --> rgb.x = rgb.x * curves[idx];

Instead of indexing uniform array with 0, I index it with variable idx, which is equal to 0 too - it fails to load the shader with
"RuntimeEffect error" here:

var program = await FragmentProgram.fromAsset('shaders/image_processor.frag');

So it isn't possible to index uniform array with a variable - while I think this should be possible in GLSL.
Tried setting version 460 - doesn't work too.

Flutter Doctor output

Doctor output

$ flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 3.22.0, on Microsoft Windows [Version 10.0.19045.4291], locale en-US)
[√] Windows Version (Installed version of Windows is version 10 or higher)
[√] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[√] Chrome - develop for the web
[√] Android Studio (version 2021.2)
[√] Android Studio (version 2023.2)
[√] VS Code (version 1.89.1)      
[√] Connected device (3 available)
[√] Network resources

! Doctor found issues in 1 category.

[curvednebula]

It seems that this is a limitation of GLSL before v4.0:
https://stackoverflow.com/questions/45167538/error-sampler-arrays-indexed-with-non-constant-expressions-are-forbidden-in-gl

[curvednebula]

I just wanted to say that indexing uniform array with variables is a very useful/needed feature in shaders. Overwise you need to pack somehow float array into image and pass it as texture to shader (you can index pixels of the texture with variables) - but this will require many operations to convert float array into array of 4 byte RGBA pixels -> which will be converted into 4 normalized extra low precision floats in the shader -> then convert them into one normal precision float