GLTFExporter: Add dispersion support. (#28057)

examples/jsm/exporters/GLTFExporter.js

@@ -111,6 +111,12 @@ class GLTFExporter {
 
 		} );
 
+		this.register( function ( writer ) {
+
+			return new GLTFMaterialsDispersionExtension( writer );
+
+		} );
+
 		this.register( function ( writer ) {
 
 			return new GLTFMaterialsIridescenceExtension( writer );
@@ -2648,6 +2654,40 @@ class GLTFMaterialsClearcoatExtension {
 
 }
 
+/**
+ * Materials dispersion Extension
+ *
+ * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_dispersion
+ */
+class GLTFMaterialsDispersionExtension {
+
+	constructor( writer ) {
+
+		this.writer = writer;
+		this.name = 'KHR_materials_dispersion';
+
+	}
+
+	writeMaterial( material, materialDef ) {
+
+		if ( ! material.isMeshPhysicalMaterial || material.dispersion === 0 ) return;
+
+		const writer = this.writer;
+		const extensionsUsed = writer.extensionsUsed;
+
+		const extensionDef = {};
+
+		extensionDef.dispersion = material.dispersion;
+
+		materialDef.extensions = materialDef.extensions || {};
+		materialDef.extensions[ this.name ] = extensionDef;
+
+		extensionsUsed[ this.name ] = true;
+
+	}
+
+}
+
 /**
  * Iridescence Materials Extension
  *