Item shader with roughness

src/components/GenericShape.tsx

@@ -1,8 +1,11 @@
 import { Suspense } from "react";
 import { useGLTF, useTexture } from "@react-three/drei";
 import { BASE_URL, shapeTextureToUrl, shapeToUrl } from "../loaders";
-import { setupColor } from "../textureUtils";
 import { filterGeometryByVertexGroups, getHullBoneIndices } from "../meshUtils";
+import {
+  createAlphaAsRoughnessMaterial,
+  setupAlphaAsRoughnessTexture,
+} from "../shaderMaterials";
 import { MeshStandardMaterial } from "three";
 
 const FALLBACK_URL = `${BASE_URL}/black.png`;
@@ -21,11 +24,15 @@ export function ShapeTexture({
   material?: MeshStandardMaterial;
 }) {
   const url = shapeTextureToUrl(material.name, FALLBACK_URL);
-  const texture = useTexture(url, (texture) => setupColor(texture));
-  material.map = texture;
-  material.side = 2;
-  material.transparent = true;
-  return <primitive object={material} attach="material" />;
+  const texture = useTexture(url, (texture) =>
+    setupAlphaAsRoughnessTexture(texture)
+  );
+
+  // Create or reuse shader material that uses alpha channel as roughness
+  const shaderMaterial = createAlphaAsRoughnessMaterial();
+  shaderMaterial.map = texture;
+
+  return <primitive object={shaderMaterial} attach="material" />;
 }
 
 export function ShapeModel({ shapeName }: { shapeName: string }) {

src/shaderMaterials.ts

@@ -0,0 +1,57 @@
+import {
+  MeshStandardMaterial,
+  Texture,
+  RepeatWrapping,
+  LinearFilter,
+  LinearMipmapLinearFilter,
+  SRGBColorSpace,
+} from "three";
+
+// Shared shader modification function to avoid duplication
+const alphaAsRoughnessShaderModifier = (shader: any) => {
+  // Modify fragment shader to extract alpha channel as roughness after map is sampled
+  // We need to intercept after diffuseColor is set from the map
+  shader.fragmentShader = shader.fragmentShader.replace(
+    "#include <roughness_fragment>",
+    `
+    #include <roughness_fragment>
+    // Override roughness with map alpha channel if map exists
+    #ifdef USE_MAP
+      roughnessFactor = texture2D(map, vMapUv).a * 1;
+    #endif
+    `
+  );
+};
+
+/**
+ * Configures a texture for use with alpha-as-roughness materials
+ * @param texture - The texture to configure
+ */
+export function setupAlphaAsRoughnessTexture(texture: Texture) {
+  texture.wrapS = texture.wrapT = RepeatWrapping;
+  texture.colorSpace = SRGBColorSpace;
+  texture.flipY = false;
+  texture.anisotropy = 16;
+  texture.generateMipmaps = true;
+  texture.minFilter = LinearMipmapLinearFilter;
+  texture.magFilter = LinearFilter;
+  texture.needsUpdate = true;
+}
+
+/**
+ * Creates a reusable shader-enhanced material that treats alpha as roughness
+ * The same material instance can be used with different textures by setting the `map` property
+ * @returns A pre-configured MeshStandardMaterial with the shader modifier attached
+ */
+export function createAlphaAsRoughnessMaterial() {
+  const material = new MeshStandardMaterial({
+    side: 2, // DoubleSide
+    metalness: 0.0,
+    roughness: 1.0,
+  });
+
+  // Attach shader modifier (will be applied when shader is compiled)
+  material.onBeforeCompile = alphaAsRoughnessShaderModifier;
+
+  return material;
+}