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When querying the keycode produced by a scancode with a certain set of modifiers, it would fall back to defaults if a key hash value with the exact set of modifiers wasn't found, which resulted in certain modifier combination returning incorrect keycodes on non-ANSI keyboard layouts. For example, querying SDL_SCANCODE_Y with the alt modifier on a QWERTZ layout returns SDLK_Y instead of SDLK_Z on most platforms, as the backends don't generate a specific entry for this key + modifier combo, so the lookup would fall back to the default ANSI layout. Adding additional key+modifier combinations when building the keymap is one solution, but it makes an already expensive operation even more so, pushing the time needed to build the keymap into double-digit milliseconds in some cases due to the large amount of key combos that need to be queried, most of which are redundant. Instead, falling back to searching through the shift levels for the given modifier state when querying the keymap will ensure that the most appropriate keycode is returned. This does add some overhead to lookups if the key doesn't have an entry with the exact set of modifiers, but it is minimal as hash table lookups are an inexpensive operation, and unnecessary lookups are avoided. In my own testing of an optimized build, the difference between best-case and worst-case performance (the latter of which is highly unlikely in real-world usage) is only a few hundred nanoseconds. Additionally, the unmodified keys are queried when pumping events, so there is no additional overhead in that case.
Simple DirectMedia Layer (SDL for short) is a cross-platform library designed to make it easy to write multi-media software, such as games and emulators.
You can find the latest release and additional information at: https://www.libsdl.org/
Installation instructions and a quick introduction is available in INSTALL.md
This library is distributed under the terms of the zlib license, available in LICENSE.txt.
Enjoy!
Sam Lantinga (slouken@libsdl.org)