* Remove undrawn quads from the skybox mesh
CCSkybox had been implemented using a combination of two
inconsistent techniques. The rendering was being achieved via use of
the vertex shader's inherent support for cubemaps. That technique requires
only a single screen-covering quad, but the implemtation defined a cube.
Defining a cube mesh would be appropriate if one were simply mapping the
cubemap's 6 textures to faces, but is unnecessary if using the shader's
cubemap feature.
Not only was the use of a cube mesh unnecessary, but the particular way
the cube was defined and used meant that only one face would ever
contribute to the rendering. One of the other faces would always be culled
and the other four would be viewed edge on, mapping the the infinitesimally
thin lines defining the edges of the screen.
This commit simply removes the never-rendered faces, and adds comments
explaining the technique.
* Within test code, remove setScale calls applied to skyboxes.
A Skybox is defined in such a way that it's position, rotation and
scaling has no effect on it's rendering, so setScale has no effect.
The calls are removed from test code to avoid confusing anyone using
it as a template for their own programs.
* Make the Skybox correctly account for the camera's fov
The Skybox does not use the model/view and projection matricies. Instead
a single quad that maps exactly to the screen is rendered and the camera's
world matrix is passed into a shader that renders using cubemap lookups.
The way that works hardwires the fov to 90deg in both the horizontal and
vertical. That shows up particularly badly when the camera is pointed
directly downwards and rotated: the image deforms as it rotates.
This commit corrects the problem by using scaling factors from the
camera's projection matrix to prescale the matrix passed into the shader.
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