Multipass

[Robadob]

Hoping to implement multi-pass render support in a reconfiguration of Scene similar to this.

Should hopefully be rather painless, just need to make sure the way buffers are passed from 1 shader to the next is clean.

[Robadob]

Code is written, pending debugging to get a simple demo to actually work.

Need to fix hardcoded depthStencil format and lack of multisampling prior to merge.

[Robadob]

Code works, just finalising the example scene before squash-merge.

[Robadob]

Shadows now work largely as intended, here's a short list of what I deem remaining tasks before PR/Squash-Merge

• Review exponent rendering paper, confirm all steps followed
  • ~2k x 2k tex~
  • ~5x5 Gauss~
  • ~mip map with trilinear filtering (+ anisotropic?)~
  • Skip section 3 detection of failure (and replacement with 2x2 PCF)
• Review differences between master and branch
  • Cleanup/Refactor/Comment code
• ~Replace deer model with something high poly~ This can wait till we have proper model loading, too many higher poly models split the obj mesh into components with separate textures/materials.
• ~Implement a textured version of the shadow shader~
• ~Recolor the plane to be white~
• ~Test whether we can implement light as a spotlight, rather than a generic light at infinite distance.~ Requires a bunch of changes that aren't important enough to bother with right now.
• ~See about fixing the issue created by fixing the specular in soft shadows. (pass both hard and soft shadow maps?)~ No, Exponent paper is about hard shadows.
• ~Switch main to allow launching of both scenes~
• ~Handle inverted texcoord.y in Spirte2d.frag~
  • ~Can we invert image rows on load?~
  • ~e.g. this: http://www.gribblegames.com/articles/game_programming/sdlgl/invert_sdl_surfaces.html~
• ~Clarify Gauss methods (E.g. current method is single channel)~

[Robadob]

P.S. This lacks support for cubemap framebuffers, can be added if George requires.