WebGLRenderer: Add support for changing the assigned render target depth texture (#28584)

* Add support for swapping depth textures

* Don't swap textures if cube target

* Don't recreate render buffers

* Only attach the buffers if they have been created already

* remove unused argument

* Don't rebind the buffers if we can

* Handle cases where the depth texture is disposed and unbound

src/renderers/WebGLRenderer.js

@@ -2260,6 +2260,28 @@ class WebGLRenderer {
 					// Color and depth texture must be rebound in order for the swapchain to update.
 					textures.rebindTextures( renderTarget, properties.get( renderTarget.texture ).__webglTexture, properties.get( renderTarget.depthTexture ).__webglTexture );
 
+				} else if ( renderTarget.depthBuffer ) {
+
+					// check if the depth texture is already bound to the frame buffer and that it's been initialized
+					const depthTexture = renderTarget.depthTexture;
+					if ( renderTargetProperties.__boundDepthTexture !== depthTexture ) {
+
+						// check if the depth texture is compatible
+						if (
+							depthTexture !== null &&
+							properties.has( depthTexture ) &&
+							( renderTarget.width !== depthTexture.image.width || renderTarget.height !== depthTexture.image.height )
+						) {
+
+							throw new Error( 'WebGLRenderTarget: Attached DepthTexture is initialized to the incorrect size.' );
+
+						}
+
+						// Swap the depth buffer to the currently attached one
+						textures.setupDepthRenderbuffer( renderTarget );
+
+					}
+
 				}
 
 				const texture = renderTarget.texture;

src/renderers/webgl/WebGLProperties.js

@@ -2,6 +2,12 @@ function WebGLProperties() {
 
 	let properties = new WeakMap();
 
+	function has( object ) {
+
+		return properties.has( object );
+
+	}
+
 	function get( object ) {
 
 		let map = properties.get( object );
@@ -36,6 +42,7 @@ function WebGLProperties() {
 	}
 
 	return {
+		has: has,
 		get: get,
 		remove: remove,
 		update: update,

src/renderers/webgl/WebGLTextures.js

@@ -1555,6 +1555,37 @@ function WebGLTextures( _gl, extensions, state, properties, capabilities, utils,
 		const renderTargetProperties = properties.get( renderTarget );
 		const isCube = ( renderTarget.isWebGLCubeRenderTarget === true );
 
+		// if the bound depth texture has changed
+		if ( renderTargetProperties.__boundDepthTexture !== renderTarget.depthTexture ) {
+
+			// fire the dispose event to get rid of stored state associated with the previously bound depth buffer
+			const depthTexture = renderTarget.depthTexture;
+			if ( renderTargetProperties.__depthDisposeCallback ) {
+
+				renderTargetProperties.__depthDisposeCallback();
+
+			}
+
+			// set up dispose listeners to track when the currently attached buffer is implicitly unbound
+			if ( depthTexture ) {
+
+				const disposeEvent = () => {
+
+					delete renderTargetProperties.__boundDepthTexture;
+					delete renderTargetProperties.__depthDisposeCallback;
+					depthTexture.removeEventListener( 'dispose', disposeEvent );
+
+				};
+
+				depthTexture.addEventListener( 'dispose', disposeEvent );
+				renderTargetProperties.__depthDisposeCallback = disposeEvent;
+
+			}
+
+			renderTargetProperties.__boundDepthTexture = depthTexture;
+
+		}
+
 		if ( renderTarget.depthTexture && ! renderTargetProperties.__autoAllocateDepthBuffer ) {
 
 			if ( isCube ) throw new Error( 'target.depthTexture not supported in Cube render targets' );
@@ -1570,16 +1601,42 @@ function WebGLTextures( _gl, extensions, state, properties, capabilities, utils,
 				for ( let i = 0; i < 6; i ++ ) {
 
 					state.bindFramebuffer( _gl.FRAMEBUFFER, renderTargetProperties.__webglFramebuffer[ i ] );
-					renderTargetProperties.__webglDepthbuffer[ i ] = _gl.createRenderbuffer();
-					setupRenderBufferStorage( renderTargetProperties.__webglDepthbuffer[ i ], renderTarget, false );
+
+					if ( renderTargetProperties.__webglDepthbuffer[ i ] === undefined ) {
+
+						renderTargetProperties.__webglDepthbuffer[ i ] = _gl.createRenderbuffer();
+						setupRenderBufferStorage( renderTargetProperties.__webglDepthbuffer[ i ], renderTarget, false );
+
+					} else {
+
+						// attach buffer if it's been created already
+						const glAttachmentType = renderTarget.stencilBuffer ? _gl.DEPTH_STENCIL_ATTACHMENT : _gl.DEPTH_ATTACHMENT;
+						const renderbuffer = renderTargetProperties.__webglDepthbuffer[ i ];
+						_gl.bindRenderbuffer( _gl.RENDERBUFFER, renderbuffer );
+						_gl.framebufferRenderbuffer( _gl.FRAMEBUFFER, glAttachmentType, _gl.RENDERBUFFER, renderbuffer );
+
+					}
 
 				}
 
 			} else {
 
 				state.bindFramebuffer( _gl.FRAMEBUFFER, renderTargetProperties.__webglFramebuffer );
-				renderTargetProperties.__webglDepthbuffer = _gl.createRenderbuffer();
-				setupRenderBufferStorage( renderTargetProperties.__webglDepthbuffer, renderTarget, false );
+
+				if ( renderTargetProperties.__webglDepthbuffer === undefined ) {
+
+					renderTargetProperties.__webglDepthbuffer = _gl.createRenderbuffer();
+					setupRenderBufferStorage( renderTargetProperties.__webglDepthbuffer, renderTarget, false );
+
+				} else {
+
+					// attach buffer if it's been created already
+					const glAttachmentType = renderTarget.stencilBuffer ? _gl.DEPTH_STENCIL_ATTACHMENT : _gl.DEPTH_ATTACHMENT;
+					const renderbuffer = renderTargetProperties.__webglDepthbuffer;
+					_gl.bindRenderbuffer( _gl.RENDERBUFFER, renderbuffer );
+					_gl.framebufferRenderbuffer( _gl.FRAMEBUFFER, glAttachmentType, _gl.RENDERBUFFER, renderbuffer );
+
+				}
 
 			}