feat: Add material.getShadowMaterial to allow users to customize shadow material

Author: 06wj

src/light/LightShadow.js

@@ -208,22 +208,28 @@ const LightShadow = Class.create(/** @lends LightShadow.prototype */{
         renderer.clear(clearColor);
         camera.updateViewProjectionMatrix();
         semantic.setCamera(camera);
-        renderer.forceMaterial = shadowMaterial;
-        this.renderShadowScene(renderer);
-        delete renderer.forceMaterial;
+        this.renderShadowScene(renderer, shadowMaterial);
         framebuffer.unbind();
         semantic.setCamera(currentCamera);
         renderer.viewport();
     },
-    renderShadowScene(renderer) {
+    renderShadowScene(renderer, shadowMaterial) {
+        const preForceMaterial = renderer.forceMaterial;
+
         const renderList = renderer.renderList;
         renderList.traverse((mesh) => {
             if (isNeedRenderMesh(mesh)) {
+                renderer.forceMaterial = mesh.material.getShadowMaterial(shadowMaterial);
                 renderer.renderMesh(mesh);
             }
         }, (instancedMeshes) => {
-            renderer.renderInstancedMeshes(instancedMeshes.filter(mesh => isNeedRenderMesh(mesh)));
+            if (instancedMeshes.length) {
+                renderer.forceMaterial = instancedMeshes[0].material.getShadowMaterial(shadowMaterial);
+                renderer.renderInstancedMeshes(instancedMeshes.filter(mesh => isNeedRenderMesh(mesh)));
+            }
         });
+
+        renderer.forceMaterial = preForceMaterial;
     },
     showShadowMap() {
         this.renderer.on('afterRender', () => {

src/material/Material.js

@@ -901,7 +901,25 @@ const Material = Class.create(/** @lends Material.prototype */ {
                 origin[key] = data[key];
             }
         }
-    }
+    },
+
+    /**
+     * 获取阴影材质，子类可重写
+     * @param {Material} shadowMaterial 通用阴影材质
+     * @return {Material}
+     */
+    getShadowMaterial(shadowMaterial) {
+        if (shadowMaterial.side !== this.side) {
+            shadowMaterial.side = this.side;
+            shadowMaterial.isDirty = true;
+        }
+
+        if (shadowMaterial.frontFace !== this.frontFace) {
+            shadowMaterial.frontFace = this.frontFace;
+            shadowMaterial.isDirty = true;
+        }
+        return shadowMaterial;
+    },
 });
 
 export default Material;