没有平面也可以添加模型。

ShadowEditor.Web/src/editor/assets/ModelPanel.jsx

@@ -59,7 +59,7 @@ class ModelPanel extends React.Component {
 
         return <div className={classNames('ModelPanel', className)}
             style={style}
-               >
+        >
             <SearchField
                 data={categoryData}
                 placeholder={_t('Search Content')}
@@ -165,12 +165,8 @@ class ModelPanel extends React.Component {
 
     // 点击场景添加
     clickSceneToAdd(obj) {
-        app.toast(_t('Please click an plane in the scene.'));
-        app.on(`intersect.ModelPanel`, intersect => {
-            if (!intersect) {
-                return;
-            }
-            app.on(`intersect.ModelPanel`, null);
+        app.on(`raycast.ModelPanel`, (intersect, event) => {
+            app.on(`raycast.ModelPanel`, null);
             obj.position.copy(intersect.point);
             this.addToCenter(obj);
         });

ShadowEditor.Web/src/event/EventList.js

@@ -78,7 +78,8 @@ var EventList = [
     'transformControlsMouseDown', // 变形控件按下鼠标键
     'transformControlsMouseUp', // 变形控件抬起鼠标键
 
-    'intersect', // 选择模型整体或部分
+    'raycast', // 光线投射（不碰到模型也会触发）
+    'intersect', // 碰撞到模型（只有碰撞到模型才会触发）
     'beforeRender', // 渲染前执行
     'afterRender', // 渲染后执行
     'animate', // 进行动画

ShadowEditor.Web/src/event/RaycastEvent.js

@@ -44,17 +44,29 @@ RaycastEvent.prototype.onMouseUp = function (event) {
         return;
     }
 
-    var domElement = app.editor.renderer.domElement;
+    let domElement = app.editor.renderer.domElement;
 
     this.mouse.x = event.offsetX / domElement.clientWidth * 2 - 1;
     this.mouse.y = -event.offsetY / domElement.clientHeight * 2 + 1;
 
     this.raycaster.setFromCamera(this.mouse, app.editor.view === 'perspective' ? app.editor.camera : app.editor.orthCamera);
 
-    var intersects = this.raycaster.intersectObjects(app.editor.scene.children, true);
+    let intersects = this.raycaster.intersectObjects(app.editor.scene.children, true);
 
     if (intersects.length > 0) {
+        app.call('raycast', this, intersects[0], event);
         app.call('intersect', this, intersects[0], event, intersects);
+    } else {
+        // 没有碰撞到任何物体，则跟y=0的平面碰撞
+        let plane = new THREE.Plane().setFromNormalAndCoplanarPoint(new THREE.Vector3(0, 1, 0), new THREE.Vector3());
+        let target = new THREE.Vector3();
+        this.raycaster.ray.intersectPlane(plane, target);
+
+        app.call('raycast', this, {
+            point: target,
+            distance: this.raycaster.ray.distanceSqToPoint(target),
+            object: null
+        }, event);
     }
 };