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.