The worker currently works by receiving GENERATE_BUFFERS messages and
will send back the same kind of message, with the generated buffers
attached. All properties of the original message are kept, so that
when a GENERATE_BUFFERS message comes back to the main thread it
is possible to know what and how the buffers where generated.
This is typically used for the `projectionTransform` matrix, and
will also be necessary when working with tiles.
The worker receives a transferable array of instructions
and sends back two transferable arrays (vertex and index buffer).
The projection transform is also sent so that when the main thread
receives the buffers from the worker it also knows which projection to
apply when rendering the geometries.
The base webgl renderer module now has two types of utilities:
* `writeXFeatureInstructions` will write a series of values in a given
typed array, which represent how a given feature will be rendered; for points,
this means position, size, color, etc.
* `writeXFeatureToBuffers` will fill up the given index & vertex buffers
with values based on the provided render instructions
As such, the logic for rendering features is:
user-input style > instructions array >(*) index/vertex buffers > draw
(*) this transformation is intended to be done on a worker.
The `WebGLHelper` class now provides a `makeProjectionTransform` method
that updates a transform to match the projection for a given frame state.
This also means that the WebGLHelper does not set the projection matrix
uniform anymore, this is the responsibility of the renderer as
the rendered coordinates will not be in world space from now on.
By default, alpha premultiplying should be done by the initial rendering
(eg quads) and not the final post processing pass.
The default post processing pass expects premultiplied color values and
will not do this operation itself.
Now the shader and program caches are simply arrays of native WebGL created objects.
The WebGLHelper simply takes the sources of the frag and vert shader and produces a program.
This removes 2 classes & reduces the general verbosity of the API.
Also a `getShaderCompilationErrors` was added on `WebGLHelper` to help debug GLSL errors.
