问题
I'm trying to have a second camera to show a "from the sky" view of an AFrame scene. I've learned how to do it using a 2D canvas for rendering, following this example:
But I wonder if this could be done without using a external <div>, something like rendering directly to some asset, or maybe directly to the texture...
My current code is:
<html>
<head>
<script src="//aframe.io/releases/0.8.2/aframe.min.js"></script>
<script>
// Original code:
// https://wirewhiz.com/how-to-use-a-cameras-output-as-a-texture-in-aframe/
//
AFRAME.registerComponent('view',{
'schema': {
canvas: {
type: 'string',
default: ''
},
// desired FPS
fps: {
type: 'number',
default: 90.0
}
},
'init': function() {
var targetEl = document.querySelector(this.data.canvas);
this.counter = 0;
this.renderer = new THREE.WebGLRenderer( { antialias: true } );
this.renderer.setPixelRatio( window.devicePixelRatio );
this.renderer.setSize( targetEl.offsetWidth, targetEl.offsetHeight );
// creates spectator canvas
targetEl.appendChild(this.renderer.domElement);
this.renderer.domElement.id = "canvas";
this.renderer.domElement.crossorigin="anonymous"
this.renderer.domElement.height=300;
this.renderer.domElement.width=400;
this.el.removeAttribute('look-controls');
this.el.removeAttribute('wasd-controls');
console.log(this.renderer.domElement);
console.log(document.querySelector('a-scene'))
},
'tick': function(time, timeDelta) {
var loopFPS = 1000.0 / timeDelta;
var hmdIsXFasterThanDesiredFPS = loopFPS / this.data.fps;
var renderEveryNthFrame = Math.round(hmdIsXFasterThanDesiredFPS);
if(this.counter % renderEveryNthFrame === 0){
this.render(timeDelta);
}
this.counter += 1;
},
'render': function(){
this.renderer.render( this.el.sceneEl.object3D , this.el.object3DMap.camera );
}
});
</script>
<body>
<a-scene physics="debug: true">
<a-plane static-body position="0 0 -4" rotation="-90 0 0" width="30" height="40"
color="yellow"></a-plane>
<a-box color="red" position="0 2 0" depth="8" width="8"></a-box>
<a-entity id="secondaryCamera" position="0 40 0" rotation="-90 0 0">
<a-camera view="canvas:#spectatorDiv;" active="false">
</a-camera>
</a-entity>
<a-entity position="0 0 10" look-controls>
<a-entity camera position="0 1.6 0" wasd-controls>
<a-entity geometry="primitive:plane; width:.2; height:.2" material="src:#canvas; opacity: .6"
position="0.2 -0.3 -0.7" rotation="0 -10 0"></a-entity>
<a-cylinder radius="2" color="green"></a-box>
</a-entity>
</a-entity>
</a-scene>
<div style="height:300px; width:400px;" id='spectatorDiv'></div>
</body>
</html>
回答1:
Check out the screenshot component implementation. Render to a render target, and then do whatever you want with the pixel data (use it as a texture inside WebGL, copy to a canvas...)
回答2:
After some tinkering and considering all suggestions, I've come to this code, that gives me what I wanted. In short, I built a component (camrenderer) that uses a canvas within the a-assets element for rendering the output of the camera. This allows any material to reference it (in the code below, see it added to a plane attached to the main camera). For ensuring the material gets updated when the rendering changes, you also need to add another component (canvas-updater) to the object acting as screen.
Therefore, the camera renderer can be referenced by any material in any component, with no extra hacks.
<html>
<head>
<script src="//aframe.io/releases/0.8.2/aframe.min.js"></script>
<script>
AFRAME.registerComponent('camrender',{
'schema': {
// desired FPS
fps: {
type: 'number',
default: 90.0
},
// Id of the canvas element used for rendering the camera
cid: {
type: 'string',
default: 'camRenderer'
},
// Height of the renderer element
height: {
type: 'number',
default: 300
},
// Width of the renderer element
width: {
type: 'number',
default: 400
}
},
'update': function(oldData) {
var data = this.data
if (oldData.cid !== data.cid) {
// Find canvas element to be used for rendering
var canvasEl = document.getElementById(this.data.cid);
// Create renderer
this.renderer = new THREE.WebGLRenderer({
antialias: true,
canvas: canvasEl
});
// Set properties for renderer DOM element
this.renderer.setPixelRatio( window.devicePixelRatio );
this.renderer.domElement.crossorigin = "anonymous";
};
if (oldData.width !== data.width || oldData.height !== data.height) {
// Set size of canvas renderer
this.renderer.setSize(data.width, data.height);
this.renderer.domElement.height = data.height;
this.renderer.domElement.width = data.width;
};
if (oldData.fps !== data.fps) {
// Set how often to call tick
this.tick = AFRAME.utils.throttleTick(this.tick, 1000 / data.fps , this);
};
},
'tick': function(time, timeDelta) {
this.renderer.render( this.el.sceneEl.object3D , this.el.object3DMap.camera );
}
});
AFRAME.registerComponent('canvas-updater', {
dependencies: ['geometry', 'material'],
tick: function () {
var el = this.el;
var material;
material = el.getObject3D('mesh').material;
if (!material.map) { return; }
material.map.needsUpdate = true;
}
});
</script>
</head>
<body>
<a-scene>
<a-assets>
<canvas id="cam2"></canvas>
</a-assets>
<a-plane position="0 0 -4" rotation="-90 0 0" width="30" height="40"
color="yellow"></a-plane>
<a-box color="red" position="0 2 0" depth="8" width="16"></a-box>
<a-box color="blue" position="0 2 6" depth="2" width="6"></a-box>
<a-entity position="0 40 0" rotation="-90 0 0">
<a-camera camrender="cid: cam2" active="false">
</a-camera>
</a-entity>
<a-entity position="0 0 10" look-controls>
<a-entity camera position="0 1.6 0" wasd-controls>
<a-entity geometry="primitive:plane; width:.2; height:.2"
material="src:#cam2; opacity: .6" canvas-updater
position="0.2 -0.3 -0.7" rotation="0 -10 0"></a-entity>
<a-cylinder radius="2" color="green"></a-cylinder>
</a-entity>
</a-entity>
</a-scene>
</body>
</html>
Notes:
Thanks to Diego Marcos who put me on-track.
Thanks to Piotr Adam Milewski who suggested using Utils.ThrottleTick, which simplifies the code a lot.
This version includes a fix for a problem found with current master (but also works with
0.8.2)I've created a npm package with this components: A-Frame Playground Components. So you can just use it instead of the script above.
来源：https://stackoverflow.com/questions/53905525/aframe-how-to-render-a-camera-to-a-texture