This is more of an FYI for @boris because it is a known issue. But, it has been affecting me and potentially others, especially on mobile devices for quite some time now. For the affected, the issue is actually more about functionality than performance. There is indeed a performance aspect to this but imho even the trivial implementation solving this issue is going to perform well enough.
The basic problem comes down to that you cannot zoom‑in fully if GL_MAX_TEXTURE_SIZE is smaller than an image in one dimension.
| Zoom level | GL_MAX_TEXTURE_SIZE | |
|---|---|---|
| 2 | 16384 | 4096 |
For example, my smartphone has a limit of GL_MAX_TEXTURE_SIZE == 2048. Hence, things look even worse than in the example above (often enough without zooming‑in). Strangely enough, even Mesa 3D’s software renderer has a limit of GL_MAX_TEXTURE_SIZE == 16384 which you would normally expect to be GL_MAX_TEXTURE_SIZE == 2147483647 because this is the maximum GLint value. Eventually the Mesa 3D software renderer is going to be affected too, especially when things should evolve to GP photography. But, I am sidetracking. Low GL_MAX_TEXTURE_SIZEs on mobile devices is an existing issue that cuts into functionality.