OpenGL + SDL_TTF：纹理索引回收

Question

I am currently in the process of migrating a bunch of applications from SDL2 rendering (internally using OpenGL) to "pure" OpenGL rendering. During this work I have figured out how to upload textures to the GPU and learned that every texture has an index.

To render text I use the SDL_TTF functions that allow you to, basically, upload a texture to the GPU depicting some text. Most applications I am migrating aren't text heavy but I noticed a possible problem with them.

Imagine an application that accepts user text input and puts in on the screen: each keystroke would generate a new texture with all the text entered (any other previous texture related to the same functionality would be deleted). So, to write "Hello" we would get five textures: "H", "He", "Hel", "Hell" and finally "Hello". As said, every "previous" texture (in this case from "H" to "Hell") would be deleted and only the memory for "Hello" would remain.

Still, in text heavy applications (for example, using this method to put the score of a game, doing it badly enough that you generate a new texture for each frame) lots of textures would be uploaded and deleted and the texture index would keep on growing.

My main question here is: will OpenGL recycle those indexes or will it just run out of numbers and crash?.

PS: I am aware of the possibility of packing all the TTF characters into an atlas and just get the letters I need. I wouldn't like looking into that now unless my current approach is dangerous (this atlas thing sort of feels like old bitmap fonts).

PS2: I am also aware that changing textures constantly isn't exactly performant (GPU wise) but these applications aren't graphically challenging and have good performance in older systems.

Answer 1

OpenGL objects are referred to by what the OpenGL specification calls "names" (other often used terms in programming are "handle" or "id"/"identifier"). When a new name is first bound (with glBind… ) a corresponding OpenGL object (texture, buffer, etc.) is created; some OpenGL functions create objects and return the name to it ( glCreate… ). After a (valid) name is deleted (with glDelete… ) the corresponding OpenGL object will be deallocated once the last internal reference to it gets released. Names may be validly reused (by OpenGL) after deleting them, thereafter referring to a different object.

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Don't reinvent the wheel. Text rendering with OpenGL is ridiculously convoluted and there does not (yet¹) exist the one perfect method. There are however several libraries that address the texture generation and resource management problems. Do yourself a favour and use one of those. In your case freetype-gl would be the best option (IMHO): https://github.com/rougier/freetype-gl

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1: I'm currently working on a new shader based glyph rasterizer that addresses most of the known problems, but it's not done yet.