Transparency and Transmission in Three.js Materials

I've looked at your CodePen project and understand the issue you're facing with the reflective material not working when transparency is enabled on the back material.

When you set meshBackMat.transparent = true, the material's rendering order and blending mode change, which affects how the reflective material interacts with it.

Solution Approach

Instead of using transparent = true, you could try using an alpha map to control transparency while maintaining the transmission properties:

JAVASCRIPTCopied
// Create an alpha map for controlled transparency
const alphaMap = new THREE.TextureLoader().load('path/to/alpha_texture.png');
meshBackMat.alphaMap = alphaMap;
meshBackMat.alphaTest = 0.5; // Adjust this value as needed

The alpha map is a grayscale texture where black represents fully transparent areas and white represents fully opaque areas. This approach allows you to maintain the transmission properties needed for the reflective material to work properly.

Alternatively, you could try adjusting the material's opacity without setting transparent to true:

JAVASCRIPTCopied
meshBackMat.opacity = 0.8; // Adjust value between 0-1

If you still need to use transparent = true, you might need to adjust the rendering order of your materials and objects to ensure proper rendering:

JAVASCRIPTCopied
meshBackMat.transparent = true;
meshBackMat.depthWrite = false; // This can help with transparency rendering
meshBackMat.renderOrder = 1; // Set a higher render order for transparent objects

Remember that when using the alphaMap property, you'll need to create or find a suitable grayscale texture that defines the transparency pattern you want to achieve.