Improve custom layer compatibility

[sakitam-fdd]

Background

For #2264 mapbox custom layer integration, it introduces an external GL context for mapbox. It's exciting, but for other map engines like maptalks canvas in the GL context created externally is not rendered correctly，and I've found some reasons：

• Externally created temporary canvas does not update clientWidth and clientHeight, so I modified the following two places.
  https://github.com/uber/deck.gl/blob/4779b1040c6379c713f1a8b2d6b688b2b2909982/modules/core/src/lib/deck.js#L358
  https://github.com/uber/deck.gl/blob/4779b1040c6379c713f1a8b2d6b688b2b2909982/modules/core/src/lib/draw-layers.js#L40

  clientWidth => width
  clientHeight => height

• This is the examples maptalks.deckgl

• So I think the above modifications will have better compatibility.

To Do List

• Add label and assign to milestone
• Coding
• Doc update
• Whats new update
• Test

[ibgreen]

So I think the above modifications will have better compatibility.

@sakitam-fdd Thanks for reporting! We are of course interested in improving compatibility with other systems, however using clientWidth and clientHeight is critical in order to correctly support retina displays.

https://webglfundamentals.org/webgl/lessons/webgl-anti-patterns.html.

clientWidth represents the size of the canvas on screen, and in retina mode it will be smaller than the width and height which represent the actual size of the underlying WebGL drawing buffer, which will be scaled to the canvasWidth.

We could use width if clientWidth is not defined. But per your description, it sounds like clientWidth is defined but not updates. I am not sure how to detect that your underlying module does not update clientWidth.

[sakitam-fdd]

@ibgreen Thank you for your reply. A straightforward reason for this is that instead of drawing in a unified webgl context, it just creates an offscreen Canvas that doesn't really render canvas into the dom, and there won't be any clientWidth updates. I will think about other solutionsor and you have better suggestions?

[fuzhenn]

@ibgreen Thanks for your attention! @maptalks 's maintainer here.

The problem here is in maptalks, all the layer canvases are pre-rendered off-screen, where clientWidth and clientHeight are always 0. Meanwhile, clientWidth and clientHeight are read-only properties, so they can't be updated by upper module.

Thus it would be nice if deck.gl can fall back to canvas's width/height when clientWidth and clientHeight are 0. This should solve this off-screen canvas problem.

Thanks!

[1chandu]

Resolved by #2405

[Pessimistress]

Fix published in deck.gl@6.3.3