Applying Solid Color to Non-Textured Areas in Three.js

Based on your requirements, you want to apply a solid color to areas without texture while keeping the original texture fully visible where it exists. Here are the best approaches to achieve this effect:

1. Using AlphaMap with MeshStandardMaterial

The most straightforward approach is to use an alphaMap with a MeshStandardMaterial:

JAVASCRIPTCopied
const material = new THREE.MeshStandardMaterial({
  color: 0xff0000,  // Base color for non-textured areas
  map: textureMap,  // Your original texture
  alphaMap: alphaTexture,  // Grayscale texture defining visibility
  transparent: true
});

The alphaMap is a grayscale texture where:

• White areas (1.0) = fully opaque, showing the texture
• Black areas (0.0) = transparent, showing the base color underneath

You'll need to create an alphaMap that corresponds to your texture, where textured areas are white and non-textured areas are black.

2. Combining Color and Texture

Another approach is to use the material's color property to tint the entire object, while the texture is applied on top:

JAVASCRIPTCopied
const material = new THREE.MeshStandardMaterial({
  color: 0xff0000,  // Base color
  map: textureMap   // Your texture
});

In this case, the texture's color will be modulated by the material's color. The texture map color is adjusted by the diffuse color (material.color).

3. Custom Shader Approach

For more control, you can create a custom ShaderMaterial:

JAVASCRIPTCopied
const material = new THREE.ShaderMaterial({
  uniforms: {
    baseColor: { value: new THREE.Color(0xff0000) },
    textureMap: { value: yourTexture },
    alphaMap: { value: alphaTexture }
  },
  vertexShader: /* your vertex shader */,
  fragmentShader: `
    uniform vec3 baseColor;
    uniform sampler2D textureMap;
    uniform sampler2D alphaMap;
    
    varying vec2 vUv;
    
    void main() {
      vec4 texColor = texture2D(textureMap, vUv);
      float alpha = texture2D(alphaMap, vUv).g;  // Using green channel
      
      // Mix between base color and texture based on alpha
      vec3 finalColor = mix(baseColor, texColor.rgb, alpha);
      
      gl_FragColor = vec4(finalColor, 1.0);
    }
  `
});

This gives you precise control over how the colors blend.

Recommendation

Based on your image and requirements, I recommend the alphaMap approach as it's the most flexible and doesn't require custom shaders. You'll need to:

1. Create an alphaMap that defines where your texture should be visible
2. Set up a MeshStandardMaterial with your base color and texture
3. Apply the alphaMap to control the visibility

This approach allows you to clearly define which areas should show the texture and which should show the solid color.