Error message: The index expression for the Three.js array must be a constant value

Question

Error message: The index expression for the Three.js array must be a constant value

Encountered an issue with Three.js where using an array with a non-constant index resulted in the error message:

'[]' : Index expression must be constant

When working with the following fragment shader:

precision mediump float;

varying vec2 vUV;

uniform vec2 screenResolution;

vec4 colors[2];

void main(void) {

    vec2 uv = gl_FragCoord.xy / screenResolution.xy;

    colors[0] = vec4(0.0);
    colors[1] = vec4(1.0);

    int index = int(floor(uv.y * 1.9));

    gl_FragColor = colors[index];
}

This error did not occur when using Babylon.js.

Is it now possible to use non-constant indices for arrays in newer versions of GLSL ES, even though it was not supported before?

How can I determine the GLSL versions utilized by Three.js and Babylon.js?

javascript three.js glsl shader webgl

Answer 1

Answer №1

Short answer

To implement GLSL ES 3.0 in Three.js, it is necessary to establish a WebGL 2.0 context.

If WebGL 2 is supported by the device, the next step is to create a WebGLRenderer using the provided webgl2 context:

var canvas = document.createElement( 'canvas' );
var context = canvas.getContext( 'webgl2' );
var renderer = new THREE.WebGLRenderer( { canvas: canvas, context: context } );

Refer to Three.js documentation for more details: How to use WebGL2.

Long answer

The shader version mentioned in the query is GLSL ES 1.0. With this version, array indices must be constant-expressions.

For detailed specifications on OpenGL ES Shading Language 1.00, you can visit this link.

5 Indexing of Arrays, Vectors and Matrices

Constant-index-expressions are essential for proper array indexing according to the specification.

In GLSL ES 3.0, dynamic indexing support for arrays has been mandated, unlike the restrictions in previous versions as outlined in OpenGL ES Shading Language 3.00 - 12.30 Dynamic Indexing.

It's important to declare the GLSL ES 3.0 shader with the version qualifier at the beginning of the code:

#version 300 es

Furthermore, note that syntax differences exist in GLSL ES 3.0 compared to earlier versions, such as using in and out qualifiers for shader inputs and outputs instead of attribute or varying.

Implementing GLSL ES 3.0 requires setting up a WebGL 2.0 context.
Consult the Three.js documentation for instructions: How to use WebGL2.

Answer 2

Short answer

To implement GLSL ES 3.0 in Three.js, it is necessary to establish a WebGL 2.0 context.

If WebGL 2 is supported by the device, the next step is to create a WebGLRenderer using the provided webgl2 context:

var canvas = document.createElement( 'canvas' );
var context = canvas.getContext( 'webgl2' );
var renderer = new THREE.WebGLRenderer( { canvas: canvas, context: context } );

Refer to Three.js documentation for more details: How to use WebGL2.

Long answer

The shader version mentioned in the query is GLSL ES 1.0. With this version, array indices must be constant-expressions.

For detailed specifications on OpenGL ES Shading Language 1.00, you can visit this link.

5 Indexing of Arrays, Vectors and Matrices

Constant-index-expressions are essential for proper array indexing according to the specification.

In GLSL ES 3.0, dynamic indexing support for arrays has been mandated, unlike the restrictions in previous versions as outlined in OpenGL ES Shading Language 3.00 - 12.30 Dynamic Indexing.

It's important to declare the GLSL ES 3.0 shader with the version qualifier at the beginning of the code:

#version 300 es

Furthermore, note that syntax differences exist in GLSL ES 3.0 compared to earlier versions, such as using in and out qualifiers for shader inputs and outputs instead of attribute or varying.

Implementing GLSL ES 3.0 requires setting up a WebGL 2.0 context.
Consult the Three.js documentation for instructions: How to use WebGL2.

Error message: The index expression for the Three.js array must be a constant value

Answer №1

Short answer

Long answer

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