Render to texture

[fjtrujy]

Implement an easy way of using render to Texture

[rickgaiser]

I would like to see a more generic approach of buffers in vram. Each buffer has:

• Width
• Height
• PSM
• Vram
  Just like GSTEXTURE.

Each buffer can be:

• Framebuffer (2k aligned)
• Z buffer (2k aligned)
• Texture buffer (64 words aligned)
• CLUT buffer (64 words aligned)

We should be able to use all buffers for all puposes, assuming a 2k alignment during buffer creation:

GSTEXTURE *tex, *disp;

// Display this buffer
gsKit_setDisplayBuffer(gsGlobal, disp);

// Simple rendering
gsKit_setRenderBuffer(gsGlobal, disp);          // render to display buffer
gsKit_prim_sprite_texture(gsGlobal, tex, ...);  // render texture to display

// Render to texture
gsKit_setRenderBuffer(tex);                     // render to texture
gsKit_prim_sprite_texture(gsGlobal, disp, ...); // render from display 'texture' to texture

We can add 2 GSTEXTURE objects in gsGlobal that represent the display/render buffers as GSTEXTURE objects, making it instantly possible to use them as textures.

Then as a second step we can start using GSTEXTURE object for render/display/texture functions, just like the functions you have created. But instead of two gsKit_renderToScreen and gsKit_renderToTexture we can then have 1 gsKit_setRenderBuffer.

[fjtrujy]

Closing this PR as I think current gskit is not in a state where that functionality can be easily implemented, so I will put the functions in the repos where I'm using it