So I am making a fairly complex 2d game using modern OpenGL. Right now I am passing a VBO with model matrix, texture cords etc. for all of my sprites (it’s an “Entity” based game so everything is essentially a sprite) to the shader and using glDrawElements to draw them. Everything is working fine and I can draw many thousands of transformed sprites and I have a camera system working with zoom etc. However, I am using a single sampler2D uniform with my texture atlas. The problem is that I want to be able to use multiple texture atlases. How do other games/engines handle this?
The only thing I can think of is something like this:
I know I can have up to GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS textures bound, but in order to draw them I need to set a sampler2D uniform for each texture and pass them to the shader. Then, in the shader I need to know which sampler2D to use when I draw. I somehow need to figure this out based on what data I have in my VBO (I assume I would pass a texture id or something for each vertex). Is this approach even possible using glDrawElements, is there a better/sane way to do this? I realize that I could sort my sprites by texture atlas and use multiple glDrawElement calls, but the problem is I need the sprites to be in a specific order for layering.
If this isn’t very clear please let me know so I can try and reword it. I am new to OpenGL so it’s hard for me to explain what I am trying to do when I don’t even know what I’m doing.
