Skydome projection to allow dome / box sky texture projections

[mvaligursky]

Fixes #5160

• skydome projection, allowing cubemap to be rendered into a dome or a box

New API

Scene.sky.type  // SKYMESH_INFINITE, SKYMESH_BOX, SKYMESH_DOME
Scene.sky.node // GraphNode with transformation (ignored for INFINITE)
Scene.sky.center - center of the dome (tripod)  (ignored for INFINITE)

Note that the sky settings are now in a standalone Scene.sky object. In the future, all sky properties will be moved here instead of being in the Scene directly. This will give us the option to set an instance of an object like this on a camera for example, allowing different sky settings per camera.

Typical use:

        // setup dome based sky
        app.scene.sky.type = pc.SKYTYPE_DOME;
        app.scene.sky.node.setLocalScale(200, 200, 200);
        app.scene.sky.center = new pc.Vec3(0, 0.05, 0);

Skybox example with controls over the parameters:

Dome:

Box:

Infinite:

Fixes #5160

[willeastcott]

Do we plan to have a SKYMESH_CUSTOM for a user-supplied mesh?

[mvaligursky]

Do we plan to have a SKYMESH_CUSTOM for a user-supplied mesh?

It's definitely an option to add that was discussed, but in a separate PR

[willeastcott]

LGTM! 🚀 But please get 1 more review before merging.

[mvaligursky]

@willeastcott thanks for all the comments, all done.