Sampling Texture Colors for BufferGeometry Vertex Colors

Based on the information available, there isn't a built-in method in Three.js specifically for sampling texture colors at vertex positions to create a color buffer attribute. However, I can suggest an approach to accomplish this task.

Approach to Sample Texture Colors at Vertices

You'll need to:

1. Access the UV coordinates for each vertex in your geometry
2. Sample the texture at those UV coordinates
3. Create a new color buffer attribute with the sampled colors

Here's a code example that demonstrates this approach:

JAVASCRIPTCopied
function createVertexColorsFromTexture(geometry, texture) {
    // Ensure the texture is loaded
    if (!texture.image || !texture.image.complete) {
        console.error('Texture not loaded yet');
        return;
    }
    
    // Create a canvas to sample the texture
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');
    canvas.width = texture.image.width;
    canvas.height = texture.image.height;
    ctx.drawImage(texture.image, 0, 0);
    
    // Get the position and uv attributes
    const positions = geometry.attributes.position;
    const uvs = geometry.attributes.uv;
    
    if (!uvs) {
        console.error('Geometry does not have UV coordinates');
        return;
    }
    
    // Create a new color attribute
    const colors = new Float32Array(positions.count * 3);
    
    // Sample the texture at each vertex UV
    for (let i = 0; i < positions.count; i++) {
        const u = uvs.getX(i);
        const v = 1 - uvs.getY(i); // Flip Y for canvas coordinates
        
        // Sample the texture
        const x = Math.floor(u * canvas.width);
        const y = Math.floor(v * canvas.height);
        const pixelData = ctx.getImageData(x, y, 1, 1).data;
        
        // Set the color (normalize RGB values to 0-1 range)
        colors[i * 3] = pixelData[0] / 255;
        colors[i * 3 + 1] = pixelData[1] / 255;
        colors[i * 3 + 2] = pixelData[2] / 255;
    }
    
    // Add the color attribute to the geometry
    geometry.setAttribute('color', new THREE.BufferAttribute(colors, 3));
    
    return geometry;
}

Usage Example

JAVASCRIPTCopied
// Assuming you have a geometry and texture already set up
const geometry = yourParametricGeometry;
const texture = yourTexture;

// Make sure the texture is loaded before sampling
texture.onLoad = function() {
    createVertexColorsFromTexture(geometry, texture);
    
    // Update your material to use vertex colors
    material.vertexColors = true;
    
    // Now your geometry has vertex colors that can be exported
    // Use FBXExporter or your preferred exporter
};

Note that this approach has some limitations:

• It only samples at exact UV coordinates, which might not capture all texture details
• It requires the texture to be loaded and accessible via JavaScript
• For complex textures, you might need to consider texture filtering or sampling multiple points

For exporting to FBX with vertex colors, you'll need to use the FBXExporter from the Three.js examples, ensuring that the vertex colors are properly included in the export.