Multiple Globe updates

[bagnell]

The globe can be updated multiple times in a single frame to get terrain tiles for multiple render passes, for example, multiple camera views, viewports, framebuffers, etc.

scene.globe.initialize(frameState);

updateEnvironment(scene);

// set viewport/camera/ framebuffer

updatePrimitives(scene);
createPotentiallyVisibleSet(scene);
updateAndClearFramebuffers(scene, passState, color);
executeComputeCommands(scene);
executeCommands(scene, passState);

// update viewport/camera/framebuffer

updatePrimitives(scene);
createPotentiallyVisibleSet(scene);
executeCommands(scene, passState);

// any more updates/renders

resolveFramebuffers(scene, passState);
executeOverlayCommands(scene, passState);

scene.globe.finalize(frameState);

Globe.initialize and Globe.finalize (I'm open to name suggestions) will set up the globe for rendering and manage tile loading/unloading which only happens once per frame. Globe.update selects already loaded tiles for rendering based on the current view.

For #2594 and the infinite-2D branch.

[pjcozzi]

Nice, I'll look at this later today. @lilleyse can you review to see how this will work with your shadow changes?

[lilleyse]

Yeah I'll check this out soon.

[pjcozzi]

I would like to get this into 3d-tiles soon (a branch off of 3d-tiles, then a pull request). What is the best approach? @bagnell do you want to do it? @lilleyse or would you rather do it to get more experience with this change?

[pjcozzi]

In order to get this into 3D Tiles, we might need to add a separate primitive collection, e.g., scene.tilesets so that we can call initialize and finalize. Open to other ideas.

[pjcozzi]

As for naming, instead of initialize/finalize consider beginFrame/endFrame, the semantics better describe the lifetime (e.g. is initialize like a constructor function, and finalize like in Java?). I am tempted to name them something even more specific, but I don't know that we can really predict that much about their implementation.

[pjcozzi]

That's all my comments. @lilleyse can review and merge when ready.

[lilleyse]

Maybe not relevant to this PR, but is this a check we should be doing scene-wide?

[lilleyse]

Also perhaps this should be a helper function since it comes up 3 times.

        if (!this.show) {
            return;
        }

        var context = frameState.context;
        var width = context.drawingBufferWidth;
        var height = context.drawingBufferHeight;

        if (width === 0 || height === 0) {
            return;
        }

[pjcozzi]

This seemed odd to me too.

[bagnell]

...but is this a check we should be doing scene-wide?

The code in Globe is some of the oldest in Cesium and this was probably a workaround that was never removed. I'm going to remove it since, you're right, this should be a scene-wide check.

[lilleyse]

It might be helpful to add comments above initialize, update, and finalize eventually.

[lilleyse]

There should be a test that checks the new functionality by calling update multiple times during a single frame.

[lilleyse]

That's all from me.

[bagnell]

@lilleyse I can't think of a good test that would fail in master and pass here. I'm going to wait for the infinitely scrolling 2D for a good test. I can place the camera near the edge of the map in 2D and in master the pixel would be the background color but with multiple updates it would be the color of the imagery.

I have updated everything else from the comments.

[lilleyse]

Ok sounds good to me.

[pjcozzi]

What's the plan for merging this into 3d-tiles?

[lilleyse]

Just to make sure, does merging into 3d-tiles mean providing similar functionality for Cesium3DTileset?

[pjcozzi]

Yes, I think we'll want to do beginFrame/endFrame for 3D Tiles sooner rather than later so they work with shadows and we have a better framework for cache replacement.

[lilleyse]

I can work on bringing this into 3d-tiles.

[pjcozzi]

👍 Thanks.