Demonstrates the OpenGL feature of transform feedback using GLUtil & Vinyl-GL. Transform feedback lets you read things shader programs have computed on the GPU, normally not sent back to the CPU.
This enables hacky GPGPU computing that's appropriate for programs that are already using OpenGL for graphics, where a full-blown GPGPU API may be a burden or the computation being done is easy enough to write on a shader. Practitioners may or may not embrace black magic.
GLFW is used for the rendering context. It can be substituted for whatever you normally use (SDL, GLUT).
Once built, copy the binary & the etc folder into a fixed directory.
Run the executable from the shell, or the shaders may not be loaded.
The examples run. It's pretty idiomatic with GLUtil, but not in a completely general way. Integration with the Vinyl-GL idiom needs to be done, which should generate the configuration of the buffers during creation & extraction, & of the shader program for setting feedback varyings. This entails interpreting records in ways that will generate the strides & maybe offset to read from the buffers at, which is part of the usual job of Vinyl-GL, and would use the generalized GLUtil-idiomatic calculations. However, those parameters would just cloud these examples, since the buffers are only holding values from one output variable of the shader. Thus, they are not exposed in the GLUtil-idiomatic calculations.
The examples are designed for use only with InterleavedAttribs
as the transform feedback buffer mode, and with a specified number
of outputs to obtain from feedback, rather than a calculation of
the number of outputs that will be received, which may depend on
the shader pipeline or on the shaders themselves. This calculation
could be addressed in a number of situations, if not completely
generally.
For ideas on how Haskell's transform feedback capabilities can develop further, as well as an idea of what the raw OpenGL would look like, please cross-reference with open.gl/feedback. An expository cross-examination between that and a Haskell example may come in the future.