Cleanup renderer object creation

[pjcozzi]

Some objects use a create function like context.createRenderState; others have an explicit cache like context.getShaderCache().getShaderProgram; and others are just allocated with new like DrawCommand.

Likewise, some things need destroy, others need release, and others do not require anything.

As we add more caching (CC #638), we'll be able to converge. Details TBA.

[pjcozzi]

In addition material creation is inconsistent with the rest of Cesium.

[pjcozzi]

4ac0a1e made a minor incremental improvement so shader programs are created with context.createShaderProgram and destroyed with destroy. Under the hood they are still cached.

Since the renderer is @private, we can address this further later.

[pjcozzi]

Temporarily removed the Material texture cache: #2850

[pjcozzi]

@lilleyse, let's do a pull request for each bullet:

• createRenderbuffer / createFramebuffer
• createVertexArray / createVertexArrayFromGeometry
• createRenderState
• createTexture2D / createTexture2DFromFramebuffer / createCubeMap
• createShaderProgram / replaceShaderProgram
• createSampler
• createVertexBuffer / createIndexBuffer

[pjcozzi]

@lilleyse here's a few ideas for createRenderState:

• Remove context.createRenderState, of course.
• Change the RenderState constructor function to take options, which will have two properties: context and renderState. However, users will not call this directly, instead...
• Add RenderState.fromCache (which is a static function, not on the prototype), which takes the same options and is basically the implementation of context.createRenderState. Make sure to move the actual cache from Context.js:

var nextRenderStateId = 0;
var renderStateCache = {};

• I'm not 100% convinced that this actually works with multiple WebGL contexts, but I didn't look closely and I am not aware of any bugs. Think it through, and if there are issues, we can simply move the caches to be per context.

[pjcozzi]

@lilleyse createCubeMap should be straightforward, do it before 2D textures. Just move the implementation into the CubeMap constructor function, and then update everything. There will only be a few places; cube maps are just used for stars and in the tests.

[pjcozzi]

@lilleyse createTexture2D / createTexture2DFromFramebuffer will also be pretty straightforward. The only thing of note is to move createTexture2DFromFramebuffer to a static function, Texture.fromFramebuffer.

[pjcozzi]

@lilleyse for createShaderProgram / replaceShaderProgram, replace them with new ShaderProgram.fromCache and ShaderProgram.replaceCache static functions.

We'll talk in person about createSampler, createVertexBuffer, and createIndexBuffer. Basically, we'll create a new Sampler class, and then we need to think about buffers in context with WebGL 2 uniform buffers and transform feedback.

[lilleyse]

It seems safe to move the cache to RenderState since RenderState doesn't seem to store any GL resources. Are there any examples with multiple contexts that I could test with?

[pjcozzi]

Here's a good start (which clearly works so we are probably OK and I'm sure I thought about this at some point): http://analyticalgraphicsinc.github.io/cesium-google-earth-examples/demos/multiple/

Code: https://github.com/AnalyticalGraphicsInc/cesium-google-earth-examples/tree/master/demos/multiple

[lilleyse]

After looking closer, it does initialize its viewport width and height with the context drawing buffer's width and height. This may be a problem in some cases.

Edit: never mind, it initializes to undefined if an explicit viewport isn't given.

[pjcozzi]

@lilleyse open future pull requests into the renderer-refactor branch.

[pjcozzi]

@lilleyse for buffers, also check out the code from our book:

• https://github.com/virtualglobebook/OpenGlobe/tree/master/Source/Renderer/GL3x/Buffers
• https://github.com/virtualglobebook/OpenGlobe/tree/master/Source/Renderer/Buffers

I'm not at all advocating for the same approach, but taking a brief look should help identify strengths and weaknesses.