3d snapshot is not working because of this.contextAttr.preserveDrawingBuffer=false

[emiyalee1005]

Description of the problem

i can not snapshot the canvas by either using canvas.todataurl or stock viewer.getsnapshot() /bimsurfer also/ api,because preserveDrawingBuffer of webgl-context is set to false

xeogl version

• [ ] Dev
• [x] Master
• [ ] ...

Browser

• [x] All of them
• [ ] Chrome
• [ ] Firefox
• [ ] Internet Explorer

OS

• [x] All of them
• [ ] Windows
• [ ] Linux
• [ ] Android
• [ ] IOS

Hardware Requirements

[xeolabs]

Yes this is a tricky one because the zSpace display used by these demos only works with preserveDrawingBuffer set false.

Solution would be:

When relying on the default Scene provided by xeogl, then we would be able to configure what context attributes that xeogl will set on the default Scene's canvas, ie.

xeogl.defaultContextAttr.preserveDrawingBuffer = true;

// Creates default Scene at this point, with default context attributes as defined above
var myEntity = new xeogl.Entity({...}); 

and when creating your own scene, make it so that that your `preserveDrawingBuffer can override xeogl's:

var myScene = new xeogl.Scene({
    contextAttr: {
        preserveDrawingBuffer: true
   }
});

I'll do this one after the touch events.

[xeolabs]

Just fixed this in master. xeogl now supports two snapshot modes - see these examples:

• asynchronously - works on any xeogl.Scene
• synchronously - only works with xeogl.Scene configured with preserveDrawingBuffer:true, which incurs performance penalty