Multiple Viewports

[bagnell]

Allow for multiple viewports/camera views in a single canvas.

• One SceneManager containing multiple Scenes
  • SceneManager contains all non-view dependent primitives.
    • Primitives updated once and rendered in each viewport
    • Option on each primitive to hide for any number of viewports
  • Each Scene contains a copy of view dependent primitives.
    • Includes Globe
      • All globes search terrain geometry and texture cache before requests
      • All globes have the same terrain and imagery providers?
      • Allow globes to have different terrain and imagery providers?
      • Allow for different celestial bodies? (not implemented)
    • Includes 3D Tilesets
      • All tilesets search a geometry and texture cache before requests
      • Allow different styling?
        • Each tileset will have its own style and batch table
    • Any other primitive where each vertex needs to be multiplied by a view dependent transform on the CPU.
• One Scene with a list of Viewports that contain a camera and viewport rectangle.
  • Non-view dependent primitives updated and rendered in each viewport.
  • View dependent primitives can keep a command list per-viewport after updating for each camera
    • Can not have different terrain or imagery provider
    • Can not style 3D Tilesets per viewport.

The first option is more flexible but more complex. The second option is simpler but has a couple of constraints.

• Z-order the viewports. Model after PrimitiveCollection.
• ScreenSpaceCameraController needs to know which viewport the input originated in.
• Viewport positioning.
  • Absolute values. App responsible for resizes
  • Custom positioning implementation
  • Position with CSS and hidden divs. Potentially expensive.
• Screen space passes for each viewport and for the final framebuffer.
• Allow the same primitive to have a different material in each viewport? (probably not)

[bagnell]

We have an overlay pass. Do we want to execute those on the entire canvas or each viewport? It's only used for the shadow map debug views and ViewportQuad which isn't used anywhere. Can we remove it?

Where do we put the credits by default?

[pjcozzi]

CC #3001

[bagnell]

Having different scene modes will be possible with the first option. Would it be possible with the second?

Are we maintaining backwards compatibility? It would be difficult with the first option, probably easy for the second option.

[bagnell]

All of the widgets created by Viewer are constructed with a Scene. Which viewport should they use? If there is more than one viewport, should we disable them by default? Should we require explicit creation with a scene/viewport reference?

[yoyomule]

What is the current progress?

[pjcozzi]

@yoyomule there is initial work in the viewports branch; however, it requires pretty significant changes to the core rendering engine so we couldn't justify the effort at the time. We'll revisit, but the timeline is TBA. You are welcome to pick up this work sooner if you are interested, see CONTRIBUTING.md.

[lilleyse]

Requested on the forum: https://groups.google.com/forum/#!topic/cesium-dev/vNyg1-fVvfw

[pjcozzi]

Partial support added in #6958.

[OmarShehata]

Requested again on the forum: https://groups.google.com/d/msg/cesium-dev/SUqz4UGrSMA/F-l1ZuRTBwAJ

There is a common need for monitoring system:
Users want to see more then one screen at the same time and each screen show a map in 3D or 2D and display diffrent images.
For example,the first shows satellite images in 3D ,the second shows road map in 2D, .....
They expect the multiple screens show the same data and synchronized.
The data maybe come from server or mouse ploting.

[DoubleYellowEgg]

What is the current progress?
Is there no follow-up to this question?

[ggetz]

Here's a use case on the forum where a user would like to use one DataSourceCollection (i.e. list of entities) across multple views: https://community.cesium.com/t/shareddatasources/35455/3

[mxfh]

Specifically one would like to control the culling of tileset a bit more flexibly.
Or have control over what tiles to (pre-)load by adding some unused camera focussing the areas of interest.

Memory is costly here, so adding a second viewer is not quite the option and not helping with the culling issue at all.

Out-of-frustum tiles get unloaded way to early and can cause faulty/flickering shadows in the scene.
See unity support for this as example:

CesiumGS/cesium-unity#421

and a discussion on Unity:
https://community.cesium.com/t/increase-frustrum-culling-tolerance/31570/5?u=mxfh

I'm not aware of a similar issue for JS, but having more control of Tileset culling and loading could certainly be welcome. This also affects Terrain Tiles to some lesser extent.