Fix for variable length array initialization error.

[YLouWashU]

This PR addresses the following issue:

On Mac-ARM64 computer when building from source, I got the following errors:

/tmp/Pangolin/components/pango_display/src/view.cpp:315:16: error: variable length arrays in C++ are a Clang extension [-Werror,-Wvla-cxx-extension]
  315 |     GLfloat zs[zsize];
      |                ^~~~~
/tmp/Pangolin/components/pango_display/src/view.cpp:315:16: note: initializer of 'zsize' is not a constant expression
/tmp/Pangolin/components/pango_display/src/view.cpp:314:15: note: declared here
  314 |     const int zsize = zl*zl;
      |               ^
1 error generated.

This is caused by compiler not allowing creation of variable length array.

This PR addresses this by creating a pointer that points to the data member of a std::vector.

[christian-rauch]

Would this also work if you use constexpr? And could you update the macOS runner first to reproduce the issue you are trying to fix?

[YLouWashU]

Would this also work if you use constexpr? And could you update the macOS runner first to reproduce the issue you are trying to fix?

I can't use constexpr because 'zl' is not compile time const. And also, can you remind me what is mac runner? Thanks!

[christian-rauch]

I assume you are trying to fix #985. There, we hypothesised that this is likely caused by newer macOS / AppleClang version. The CI is using macOS 14 and the issue seems to appear on macOS 15. So updating the CI pipeline here:

Pangolin/.github/workflows/build.yml

Line 19 in 122bb3e

os: [ubuntu-22.04, ubuntu-24.04, macos-14, windows-2022]

should reproduce the issue and your PR should fix the issue.

[christian-rauch]

Why do you allocate the memory through a std::vector and not malloc/free?

Or the other way around, if you already allocated the memory for the std::vector<GLfloat> why aren't you reusing this vector and just use the data pointer wherever zs is used?

Also, when you turn this into a dynamic array, you can remove the MSVC workaround above.

[christian-rauch]

I updated the runner, enabled VLA errors to have this triggered when new VLAs are added, and I replaced the zs VLA as suggested with a std::vector<> in #987. Can you check that PR if it solves your issue?

[YLouWashU]

I updated the runner, enabled VLA errors to have this triggered when new VLAs are added, and I replaced the zs VLA as suggested with a std::vector<> in #987. Can you check that PR if it solves your issue?

Thanks so much for the fix Christian! I have tested your PR on my end and it is working. Let's land yours instead. I will close this PR.

Closing because #987 is a more proper fix.