15-466 Offscreen Rendering / Framebuffer Example

This example stores high-dynamic-range (linear light) information to an offscreen buffer (in 16-bit-per-channel floating point), blurs that information to simulate single-scattering in the eye, and tone-maps the result for display.

Key implementation notes:

• a new shader, LitGlowColorTextureProgram, is used to make the headlights and taillights emit light (notice also the special loading code that sets up the scene to use this shader for those objects)
• PlayMode::draw calls framebuffers.realloc in order to keep offscreen render targets the same size as the game window
• PlayMode::draw uses glBindFramebuffer to draw to a (non-screen) framebuffer
• helper functions in Framebuffers.cpp are used to add bloom and to tone map
• notice the "full-screen triangle with no attributes" vertex shader hack used in the various full-screen shader programs in Framebuffers

Areas for modification or improvement:

• ToneMapProgram (in Framebuffers.cpp) is a good place to adjust the tone mapping curve. Several commented-out examples are there to play with.
• bloom_kernel (in Framebuffers.cpp) computes the blur kernel used for the bloom effect, while KERNEL_RADIUS sets its size.
• the strength of the bloom effect is set by the opacity of the color returned by BlurYProgram. Set it to 1.0 and you'll have an "everything looks blurry" effect instead.
• could use different kernels or sizes for BlurXProgram and BlurYProgram to make non-symmetric blurs for artistic effect
• many games compute bloom effects at lower resolution (1/2 or even 1/4) because they are blurry anyway; could consider using a shader (or glBlitFramebuffer) to downsample before blur_x_program is run and to upsample after blur_y_program is run (you'll also need a few lower-resolution temporary framebuffers to sample to/from)
• the min and max in the texelFetch functions exist because texel access beyond texture bounds is undefined unless running in robust mode; these comparisons could likely be avoided or modified to improve performance.
• could use TEXTURE_RECTANGLE instead of TEXTURE_2D for the framebuffers (nothing about the code requires the slightly increased functionality of a TEXTURE_2D)

This example uses NEST.