Add support for Cube Map Rotation and expose Skybox Rotation

[raytranuk]

Fixes #2505

Public API additions:

 * @class
 * @name pc.Scene
 *
 * @property {pc.Quat} skyboxRotation The rotation of the skybox to be displayed. Defaults to pc.Quat.IDENTITY

Example:

    var r = new pc.Quat();
    r.setFromEulerAngles(42, 42, 0);
    app.scene.skyboxRotation = r;

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[slimbuck]

As a user, I think it's confusing that setting an identity rotation matrix results in a mirror transform. I'd much rather keep the -1x always and optionally multiply in the rotation matrix.

Also, is it possible to have this rotation logic (the -1x and optional rotation matrix) encapsulated into single chunk/function? This way we can modify/customise easily in future.

[slimbuck]

Alternatively you could apply the -1x to the matrix when it's being set on the shader.

[raytranuk]

As a user, I think it's confusing that setting an identity rotation matrix results in a mirror transform. I'd much rather keep the -1x always and optionally multiply in the rotation matrix.

Also, is it possible to have this rotation logic (the -1x and optional rotation matrix) encapsulated into single chunk/function? This way we can modify/customise easily in future.

Alternatively you could apply the -1x to the matrix when it's being set on the shader.

I will move the rotation logic into a function and put it in a new chunk.

For the -1x flip, maybe the best way for users is to expose an extra boolean flag which defaults to true to determine is the -1x should be applied to the rotation - and maybe switch back to Quat from Mat3 for the rotation property?

[mvaligursky]

For the -1x flip, maybe the best way for users is to expose an extra boolean flag which defaults to true to determine is the -1x should be applied to the rotation - and maybe switch back to Quat from Mat3 for the rotation property?

yep I agree with this. Ideally we don't convert quat->matrix each frame, so it would need to store additional Mat3 as well?

[willeastcott]

Will this fully address #189?

[raytranuk]

Just curious why the docs for each property have been made single line? We normally try to make an effort for JSDoc blocks to stick to a reasonable number of columns (the coding standards never specified this maximum though). But it's good to be able to read them without having to scroll horizontally.

I restored it to multi-line

[Maksims]

PR name is misleading - this is not cubemap rotation, but skybox rotation.

Is it possible to rotate cubemap that is applied on material directly?
Box projection cubemaps been limited by not able to rotate them, leading to limited use cases. One of them is moving objects, e.g. train with box projected cubemap inside.

[raytranuk]

PR name is misleading - this is not cubemap rotation, but skybox rotation.

Is it possible to rotate cubemap that is applied on material directly?
Box projection cubemaps been limited by not able to rotate them, leading to limited use cases. One of them is moving objects, e.g. train with box projected cubemap inside.

@Maksims - You are right, this PR now only exposes skybox rotation, even though the shader code does support any cubemap to be rotated. A subsequent PR will also expose non-skybox cube map rotation - and we are discussing the best place to store the rotation. I'll adjust the name of this PR.