WebGLRenderer: Let transmissionRenderTarget size match relevant viewport size (#28088)

Co-authored-by: Noeri Huisman <[email protected]>

src/renderers/WebGLRenderer.js

@@ -24,7 +24,6 @@ import {
 import { Color } from '../math/Color.js';
 import { Frustum } from '../math/Frustum.js';
 import { Matrix4 } from '../math/Matrix4.js';
-import { Vector2 } from '../math/Vector2.js';
 import { Vector3 } from '../math/Vector3.js';
 import { Vector4 } from '../math/Vector4.js';
 import { WebGLAnimation } from './webgl/WebGLAnimation.js';
@@ -203,7 +202,6 @@ class WebGLRenderer {
 
 		const _projScreenMatrix = new Matrix4();
 
-		const _vector2 = new Vector2();
 		const _vector3 = new Vector3();
 
 		const _emptyScene = { background: null, fog: null, environment: null, overrideMaterial: null, isScene: true };
@@ -1426,8 +1424,8 @@ class WebGLRenderer {
 
 			const transmissionRenderTarget = currentRenderState.state.transmissionRenderTarget;
 
-			_this.getDrawingBufferSize( _vector2 );
-			transmissionRenderTarget.setSize( _vector2.x, _vector2.y );
+			const activeViewport = camera.viewport || _currentViewport;
+			transmissionRenderTarget.setSize( activeViewport.z, activeViewport.w );
 
 			//
 
@@ -1445,6 +1443,11 @@ class WebGLRenderer {
 			const currentToneMapping = _this.toneMapping;
 			_this.toneMapping = NoToneMapping;
 
+			// Remove viewport from camera to avoid nested render calls resetting viewport to it (e.g Reflector).
+			// Transmission render pass requires viewport to match the transmissionRenderTarget.
+			const currentCameraViewport = camera.viewport;
+			if ( camera.viewport !== undefined ) camera.viewport = undefined;
+
 			renderObjects( opaqueObjects, scene, camera );
 
 			textures.updateMultisampleRenderTarget( transmissionRenderTarget );
@@ -1490,6 +1493,8 @@ class WebGLRenderer {
 
 			_this.setClearColor( _currentClearColor, _currentClearAlpha );
 
+			if ( currentCameraViewport !== undefined ) camera.viewport = currentCameraViewport;
+
 			_this.toneMapping = currentToneMapping;
 
 		}