Updating Shared Uniforms Across Multiple ShaderMaterials

Yes, it's possible to update a single uniform (like a DataTexture) that is shared across multiple ShaderMaterial instances. This is a common approach for optimizing performance when you need to update data that affects multiple objects.

Approach Using UniformsUtils

You can leverage the UniformsUtils utility in Three.js to help manage shared uniforms. Here's how you might implement this:

1. Create a shared uniform object that contains your texture
2. Reference this same object across all your shader materials
3. Update the texture once, and all materials will see the change

Implementation Example

JAVASCRIPTCopied
// Import necessary utilities
import { UniformsUtils } from 'three/src/renderers/shaders/UniformsUtils.js';
import { DataTexture } from 'three';

// Create a shared uniform object
const sharedUniforms = {
  labelMap: { value: new DataTexture() },
  // Add any other shared uniforms you need
};

// When creating materials for each character, reference the shared uniforms
function createCharacterMaterial(individualUniforms) {
  // Merge shared uniforms with character-specific uniforms
  const uniforms = UniformsUtils.merge([
    sharedUniforms,
    individualUniforms
  ]);
  
  return new THREE.ShaderMaterial({
    uniforms: uniforms,
    vertexShader: yourVertexShader,
    fragmentShader: yourFragmentShader,
    // Other material properties
  });
}

// When you need to update the texture after repacking
function updateLabelTexture(newPackedTexture) {
  // Simply update the shared texture
  sharedUniforms.labelMap.value = newPackedTexture;
  // Or update its properties if keeping the same texture object
  sharedUniforms.labelMap.value.image = newPackedTexture.image;
  sharedUniforms.labelMap.value.needsUpdate = true;
  
  // No need to update each material individually!
}

Important Considerations

1. When using this approach, make sure your shader is designed to handle the UV mapping changes. You might need additional uniforms to tell each character where its label is in the packed texture.

2. If you're updating the texture frequently, consider using a texture atlas approach where each character has a fixed region in the texture, which might reduce the need for UV remapping.

3. For performance reasons, try to minimize the frequency of texture repacking operations, as they can be expensive.

This approach should allow you to efficiently update all your character labels by modifying a single shared texture uniform.