We cheat and just set the texture parameters instead and hope nothing
explodes.
So far it didn't.
This is only needed to support GLES 2.0 so it's quite a limited set of
hardware these days.
Instead of uploading a texture once per filter, ensure textures are
uploaded as little as possible and use samplers instead to switch
different filters.
Sometimes we have to reupload a texture unfortunately, when it is an
external one and we want to create mipmaps.
There are situations where our "default framebuffer" is not actually
zero, yet we still want to apply a scissor rect.
Generally, 0 is the default framebuffer. But on platforms where we need
to bind a platform-specific feature to a GL_FRAMEBUFFER, we might have a
default that is not 0. For example, on macOS we bind an IOSurfaceRef to
a GL_TEXTURE_RECTANGLE which then is assigned as the backing store for a
framebuffer. This is different than using gsk_gl_renderer_render_texture()
in that we don't want to incur an extra copy to the destination surface
nor do we even have a way to pass a texture_id into render_texture().
Don't pass texture + rect, but instead have
gdk_memory_texture_new_subtexture()
and use it to generate subtextures and pass them.
This has the advantage of downloading the a too large texture only once
instead of N times.
