Load file to texture & apply transformations with stacked shaders

[fenollp]

The time it takes to transmit data to GPU is non negligible.

Right now what we do is

1. mmap the file to RAM
2. create RAM buffers for vertices & colors & the indices of the elements that are worth rendering
3. transfer these buffers to GPU memory
4. draw
5. repeat

Instead we could

1. load the file into a texture (mmap on GPU?)
2. create vertices & their colors with shaders (tricky part*)
3. draw
4. repeat

This would make the host code much simpler.
Thus porting to Web or Android would be much simpler.

*The tricky part is that to do something like Algo3DCubeFrebet with shaders, one needs to somehow:

1. read multiple bytes from the file-texture
2. write a color to the output texture but at different coordinates
   I believe that (x1,y1) --> (x2,y2,z) transformation is hard for a GPU.
   Maybe compute shaders can help here?

@icehess Ideas?

[fenollp]

If shaders can be used to fill a texture then things such as https://github.com/rikusalminen/triangles/blob/613a27d047f0caba934173448260b932e33b0924/shaders/icosphere/icosphere.glslv could be used as well.

Also: https://github.com/voidstarHQ/voidstar/blob/b5182cc3758bae1ef1b718e5df37f68a40c24b12/pi.glsl

[fenollp]

https://www.khronos.org/opengl/wiki/Vertex_Texture_Fetch

[fenollp]

Some experiments at

voidstar/hacking/argh.cc

Line 401 in b5182cc

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, fW, fH, 0, GL_BGR, GL_UNSIGNED_BYTE,