[3.x] Unbind texture slots when changing framebuffer

[lawnjelly]

Prevent bugs whereby texture still in use.

Roughly based on @clayjohn's draft clayjohn@baf691a

Fixes #61632

Maintains a list of texture slots that have been bound in the current frame, so they can be unbound when setting a new render target.

Notes

• Have pushed forward with this as clayjohn is busy with 4.x
• I wasn't sure if we needed to keep it in frame.
• Rather than keeping this up to date manually I figured a wrapper might be a better bet.

Clayjohn's original draft did this:

	// Unbind user textures that have been set since the last render target change.
	// Unbind the internal slots that may have been used by  Godot.
	for (int i = 1; i <= 13; i++) {
		glActiveTexture(GL_TEXTURE0 + storage->config.max_texture_image_units - i);
		glBindTexture(GL_TEXTURE_2D, 0);
	}
	// Unbind from 0 up to the max texture slot used by the user.
	for (int i = 0; i < storage->frame.max_texture_binding + 2; i++) {
		glActiveTexture(GL_TEXTURE0 + i);
		glBindTexture(GL_TEXTURE_2D, 0);
	}

This seems likely to duplicate unbinding for a bunch of slots.

I experimented with keeping a maximum slot from the beginning and minimum from the end of the texture unit range, but decided in the end it was probably the best trade off to keep a list of slots in use. In combination with a lookup table (bitfield used here) it should be very efficient with negligible cost.

[clayjohn]

Looks great! I think the overhead of accidentally unbinding a texture slot that wasn't bound would be pretty low. But this doesn't add much more complexity to have the peace of mind that we aren't unbinding too much.

It would be nice to have this forward ported to 4.x as well.

[lawnjelly]

It would be nice to have this forward ported to 4.x as well.

Sure, it's pretty simple.

[akien-mga]

Thanks!

[harrisyu]

I found 8 errors before running a project like this:

E 0:00:00.183   RasterizerStorageGLES3::GLWrapper::gl_active_texture: Condition "(unsigned int)p_texture >= texture_unit_table.get_num_bits()" is true.
  <C++ Source>  D:\build\godot-switch\godot-nx\drivers\gles3\rasterizer_storage_gles3.h:1519 @ RasterizerStorageGLES3::GLWrapper::gl_active_texture()

I think is because
gl_wrapper.initialize() must be called before using gl_wrapper.gl_active_texture().
get_num_bits() is 0 before gl_wrapper.initialize() .

[lawnjelly]

You are correct initialize() is meant to be called before gl_active_texture(). It won't cause any problems but I'll see if I can work out where this is being called from, and see if we can initialize() earlier. 👍

[lawnjelly]

Ah yes, silly me, I must have only tested GLES2. GLES3 is calling active texture in the storage initialize before the wrapper is initialized. Will fix this (should just be initializing the wrapper earlier in the function).

Until then just ignore these messages, they are benign.