OpenGL

[katajakasa]

WIP, do not merge.

Plan:

1. Dump sprites to an RG8 texture atlas (R = color, G = alpha)
2. Dump vertices and texture coords to a VBO
3. Dump palettes and remappings to UBO(s) (or possibly consider 1D textures later for gotta go faster ?)
4. Create an R8 texture and bind it to FBO, set FBO as target.
5. Draw all objects. Shader should do any palette trickery now.
6. Switch back to default FBO, and bind the previous render target texture.
7. Ram the textuer through RGBA conversion with current palette.
8. Run any upscaler shaders we want also (scalehqx, vhs, scanline, etc).
9. Profit!

Notes:

• Currently FBO size is 320x200, and we change the viewport to match that on fbo rendering phase. If/when we do sprite packs for larger sprites, we should bump the size. Perhaps some config option ?
• When everything else works, consider using https://github.com/libretro/glsl-shaders for upscaling the result in rgba phase.

It might make sense to split the rendering into three, as the news caster guy wants images from arenas without the text and UI crap. So perhaps first render all game objects, then snatch any screenshots, and then draw the UI crap.

Cleanup TODO:

• Consider getting rid of discard in glsl shaders
• Maybe texture1d for palette + remappings instead of ubo ?
• https://www.reddit.com/r/gamedev/comments/2j17wk/a_slightly_faster_bufferless_vertex_shader_trick/
• Look into the fread() bug. Something related to windows or mingw or msys2 ?

[turol]

Prefer libepoxy over libglew. It supports GL ES too and starts up faster.

[katajakasa]

Prefer libepoxy over libglew. It supports GL ES too and starts up faster.

Interesting, I will take a look. Glew is a total pain to maintain.

[turol]

Reading from UBO with a varying offset might be a slow path. Use a texture instead. Either GL_TEXTURE_1D or a 2d texture with width or height of 1.

Using discard in shader is potentially a slow path. Prefer outputting fully transparent color instead.

[katajakasa]

Reading from UBO with a varying offset might be a slow path. Use a texture instead. Either GL_TEXTURE_1D or a 2d texture with width or height of 1.

Using discard in shader is potentially a slow path. Prefer outputting fully transparent color instead.

Interesting. I added these on my future to-do list.

[turol]

You probably want this: https://www.reddit.com/r/gamedev/comments/2j17wk/a_slightly_faster_bufferless_vertex_shader_trick/

[katajakasa]

You probably want this: https://www.reddit.com/r/gamedev/comments/2j17wk/a_slightly_faster_bufferless_vertex_shader_trick/

Lol. On to the list it goes.

[katajakasa]

Further work items are now here: #612