Add KHR_materials_unlit export support (playcanvas#8270)

willeastcott · web-flow · commit 751d8984286e · 2025-12-19T11:47:20.000Z
* Add KHR_materials_unlit export support

* Refactor adding extensions
diff --git a/src/extras/exporters/gltf-exporter.js b/src/extras/exporters/gltf-exporter.js
@@ -382,13 +382,27 @@ class GltfExporter extends CoreExporter {
         }
     }
 
+    addExtension(json, output, name, data = {}) {
+        output.extensions = output.extensions || {};
+        output.extensions[name] = data;
+
+        json.extensionsUsed = json.extensionsUsed ?? [];
+        if (!json.extensionsUsed.includes(name)) {
+            json.extensionsUsed.push(name);
+        }
+    }
+
     writeStandardMaterial(resources, mat, output, json) {
 
         const { diffuse, emissive, opacity, metalness, gloss, glossInvert } = mat;
         const pbr = output.pbrMetallicRoughness;
 
-        if (!diffuse.equals(Color.WHITE) || opacity !== 1) {
-            const { r, g, b } = diffuse.clone().linear();
+        // For unlit materials, the parser copies baseColor to emissive and sets diffuse to white.
+        // So we need to use emissive as the source for baseColorFactor.
+        const baseColor = mat.useLighting ? diffuse : emissive;
+
+        if (!baseColor.equals(Color.WHITE) || opacity !== 1) {
+            const { r, g, b } = baseColor.clone().linear();
             pbr.baseColorFactor = [r, g, b, opacity];
         }
 
@@ -401,24 +415,20 @@ class GltfExporter extends CoreExporter {
             pbr.roughnessFactor = roughness;
         }
 
-        this.attachTexture(resources, mat, pbr, 'baseColorTexture', 'diffuseMap', json);
+        // For unlit, use emissiveMap as baseColorTexture source (parser copies diffuseMap to emissiveMap)
+        this.attachTexture(resources, mat, pbr, 'baseColorTexture', mat.useLighting ? 'diffuseMap' : 'emissiveMap', json);
         this.attachTexture(resources, mat, pbr, 'metallicRoughnessTexture', 'metalnessMap', json);
 
-        if (!emissive.equals(Color.BLACK)) {
+        // Skip emissive for unlit materials (emissive holds the baseColor)
+        if (mat.useLighting && !emissive.equals(Color.BLACK)) {
             const { r, g, b } = emissive.clone().linear();
             output.emissiveFactor = [r, g, b];
         }
 
-        if (mat.emissiveIntensity !== 1) {
-            output.extensions = output.extensions || {};
-            output.extensions.KHR_materials_emissive_strength = {
+        if (mat.useLighting && mat.emissiveIntensity !== 1) {
+            this.addExtension(json, output, 'KHR_materials_emissive_strength', {
                 emissiveStrength: mat.emissiveIntensity
-            };
-
-            json.extensionsUsed = json.extensionsUsed ?? [];
-            if (!json.extensionsUsed.includes('KHR_materials_emissive_strength')) {
-                json.extensionsUsed.push('KHR_materials_emissive_strength');
-            }
+            });
         }
 
         if (mat.useMetalnessSpecularColor) {
@@ -437,15 +447,13 @@ class GltfExporter extends CoreExporter {
             this.attachTexture(resources, mat, specularExt, 'specularTexture', 'specularityFactorMap', json);
 
             if (Object.keys(specularExt).length > 0) {
-                output.extensions = output.extensions || {};
-                output.extensions.KHR_materials_specular = specularExt;
-
-                json.extensionsUsed = json.extensionsUsed ?? [];
-                if (!json.extensionsUsed.includes('KHR_materials_specular')) {
-                    json.extensionsUsed.push('KHR_materials_specular');
-                }
+                this.addExtension(json, output, 'KHR_materials_specular', specularExt);
             }
         }
+
+        if (!mat.useLighting) {
+            this.addExtension(json, output, 'KHR_materials_unlit');
+        }
     }
 
     writeMaterials(resources, json) {
