Creating a Heatmap Effect with Post-Processing in Three.js

Yes, you can definitely create a heatmap effect using a custom post-processing shader in Three.js. This approach would be more efficient than modifying individual objects, especially for complex scenes.

Using EffectComposer for Post-Processing

The EffectComposer is the key component you'll need for implementing post-processing effects in Three.js. Here's how you could approach this:

1. Set up an EffectComposer with a custom shader pass
2. Use a position buffer or depth texture to determine object positions
3. Calculate distances to your reference points in the shader
4. Apply color mapping based on those distances

Implementation Approach

JAVASCRIPTCopied
// Import necessary components
import { EffectComposer } from 'three/examples/jsm/postprocessing/EffectComposer.js';
import { RenderPass } from 'three/examples/jsm/postprocessing/RenderPass.js';
import { ShaderPass } from 'three/examples/jsm/postprocessing/ShaderPass.js';

// Set up renderer with necessary buffers
const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
// Enable position buffer if needed
renderer.outputEncoding = THREE.sRGBEncoding;

// Create composer
const composer = new EffectComposer(renderer);

// Add standard render pass
const renderPass = new RenderPass(scene, camera);
composer.addPass(renderPass);

// Create custom heatmap shader
const heatmapShader = {
  uniforms: {
    "tDiffuse": { value: null },
    "tDepth": { value: null },
    "cameraNear": { value: camera.near },
    "cameraFar": { value: camera.far },
    "heatPoints": { value: [] }, // Array of Vector3 points
    "maxDistance": { value: 10.0 }, // Maximum distance for heat effect
    "heatColors": { value: [
      new THREE.Vector3(1.0, 0.0, 0.0), // Red (hot)
      new THREE.Vector3(1.0, 1.0, 0.0), // Yellow
      new THREE.Vector3(0.0, 0.0, 1.0)  // Blue (cold)
    ]}
  },
  vertexShader: `
    varying vec2 vUv;
    void main() {
      vUv = uv;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    uniform sampler2D tDiffuse;
    uniform sampler2D tDepth;
    uniform float cameraNear;
    uniform float cameraFar;
    uniform vec3 heatPoints[10]; // Adjust size as needed
    uniform float maxDistance;
    uniform vec3 heatColors[3]; // Color gradient
    
    varying vec2 vUv;
    
    // Function to reconstruct position from depth
    vec3 getWorldPosition(float depth) {
      float z = depth * 2.0 - 1.0;
      
      vec4 clipSpacePosition = vec4(vUv * 2.0 - 1.0, z, 1.0);
      vec4 viewSpacePosition = projectionMatrixInverse * clipSpacePosition;
      
      viewSpacePosition /= viewSpacePosition.w;
      vec4 worldSpacePosition = viewMatrixInverse * viewSpacePosition;
      
      return worldSpacePosition.xyz;
    }
    
    // Function to get color based on distance
    vec3 getHeatColor(float distance) {
      float normalizedDist = clamp(distance / maxDistance, 0.0, 1.0);
      
      // Simple gradient between colors
      if (normalizedDist < 0.5) {
        return mix(heatColors[0], heatColors[1], normalizedDist * 2.0);
      } else {
        return mix(heatColors[1], heatColors[2], (normalizedDist - 0.5) * 2.0);
      }
    }
    
    void main() {
      vec4 originalColor = texture2D(tDiffuse, vUv);
      float depth = texture2D(tDepth, vUv).x;
      
      // Get world position from depth
      vec3 worldPos = getWorldPosition(depth);
      
      // Find minimum distance to any heat point
      float minDist = maxDistance;
      for (int i = 0; i < 10; i++) { // Match array size
        float dist = distance(worldPos, heatPoints[i]);
        minDist = min(minDist, dist);
      }
      
      // Apply heat color based on distance
      vec3 heatColor = getHeatColor(minDist);
      
      // Blend with original color (adjust blending as needed)
      gl_FragColor = vec4(mix(originalColor.rgb, heatColor, 0.7), originalColor.a);
    }
  `
};

// Create shader pass and add to composer
const heatmapPass = new ShaderPass(heatmapShader);
composer.addPass(heatmapPass);

// In your animation loop
function animate() {
  requestAnimationFrame(animate);
  
  // Update heat points if they move
  heatmapPass.uniforms.heatPoints.value = yourHeatPointsArray;
  
  // Render with composer instead of renderer
  composer.render();
}

Important Considerations

1. You'll need to provide the depth texture to your shader. This can be done by setting up a render target with a depth texture.

2. The shader needs access to the camera's projection and view matrices to reconstruct world positions from depth.

3. For more accurate results, you might want to use a position buffer instead of reconstructing from depth.

4. The number of heat points in the shader is fixed (10 in this example), but you can adjust this based on your needs.

This approach should give you a more efficient way to create a heatmap effect across your entire scene without modifying individual objects.