miniscule fix for building on systems where the hardcoded path to libdrm headers doesn't exist

[pillowtrucker]

, e.g. NixOS.
I hope this still works on other systems.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.52%. Comparing base (a5f3143) to head (be9edd1).

❗ Current head be9edd1 differs from pull request most recent head 9b9393e

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3387      +/-   ##
==========================================
- Coverage   77.52%   77.52%   -0.01%     
==========================================
  Files        1065     1065              
  Lines       67901    67901              
==========================================
- Hits        52639    52638       -1     
- Misses      15262    15263       +1     

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[RAOF]

Neat!

This information should be available in pkgconfig, right? I think it would be a better idea to pull it from there (as that's where the compiler will pull it from) - I'm not sure if CMake's find_path will match the pkgconfig behaviour, and things could get weird if those don't match.

[pillowtrucker]

Oh, I totally missed that there is a similar variable already set by pkg_check_modules.
The problem with that though is that it can (and does) return more than one directory, so it would still have to be something like

find_path(DRM_FOURCC_INCLUDE_DIR NAMES "drm_fourcc.h" PATH_SUFFIXES "libdrm" "" HINTS ${DRM_INCLUDE_DIRS})

which is kind of redundant, but I guess it doesn't hurt either. find_path always returns the first match, so it's guaranteed to be at most one entry. Should I make that change ?

[pillowtrucker]

Fixed up and rebuilt and briefly tested. There was a third occurrence of the hardcoded path there that I had missed which apparently didn't cause any build or runtime failure on my computer, but left the DRM_MODIFIERS_FILE incomplete, that's also been taken into account now.

[RAOF]

Thanks for the ping! This fell off my plate when travelling to the recent sprint, the week-long sprint, and then the travel back 😉

I've tweaked the find_path invocation slightly, to make it fail if it doesn't find drm_fourcc.h and to make sure it only looks in places pkgconf lists. Please check that this still works for you, and then I think this is good!

[pillowtrucker]

Yep that still builds and runs on nix. Good call, because otherwise the find_* functions first look in all of the paths in one of the CMAKE_* environment variables set by nix.

[AlanGriffiths]

Ignoring paranoid thoughts like "what if DRM_FOURCC_INCLUDE_DIR includes spaces?" this looks reasonable.

Addressed