ThreeJS后期多场景渲染

需求：场景模型需要Bloom，ssao等后期特效，但人物模型不需要。

之前做过类似的需求，一个场景伽马校正，另一个不需要，实现方式是用同一个renderer和camera， 多个scene，将renderer.autoClear = false，然后分别渲染scene1，scene2

尝试了下这套方案不可取，因为现在renderer通过后期混合器调用来渲染，然后就是一顿上网查，国内没有相关信息，google一下发现5，6年前在stackoverflow上有人问过，但不了了之..

看下了renderPass的源码：

var RenderPass = function ( scene, camera, overrideMaterial, clearColor, clearAlpha ) {

	Pass.call( this );

	this.scene = scene;
	this.camera = camera;

	this.overrideMaterial = overrideMaterial;

	this.clearColor = clearColor;
	this.clearAlpha = ( clearAlpha !== undefined ) ? clearAlpha : 0;

	this.clear = true;
	this.clearDepth = false;
	this.needsSwap = false;

};

发现RenderPass有clear属性可以利用下，新建一个renderPass在ssao后面，通过叠加的方式，可以实现需要的效果

        function initEffect() {
            let renderTargetParameters = { minFilter: THREE.LinearFilter, magFilter: THREE.LinearFilter, format: THREE.RGBAFormat, stencilBuffer: true };
            let renderTarget = new THREE.WebGLRenderTarget(window.innerWidth, window.innerHeight, renderTargetParameters);
            composer = new EffectComposer(renderer, renderTarget);

            renderPass = new RenderPass(scene, camera);
            composer.addPass(renderPass);

            var ssaoPass = new SSAOPass(scene, camera, window.innerWidth, window.innerHeight);
            ssaoPass.kernelRadius = 16;
            ssaoPass.maxDistance = 0.03;
            ssaoPass.maxDistance = 0.1;
            composer.addPass(ssaoPass);

            renderPass2 = new RenderPass(scene2, camera);
            renderPass2.clear = false
            composer.addPass(renderPass2);

            var bloomPass = new UnrealBloomPass(new THREE.Vector2(window.innerWidth, window.innerHeight));
            bloomPass.threshold = 0;
            bloomPass.strength = 0.1;
            bloomPass.radius = 0;
            composer.addPass(bloomPass);
        }

done:)