If rendering with Swiftshader, which only works for offscreen renders on MacOS due to #70, the readback works correctly and a valid image is produced. But if rendering with the hardware via MoltenVK, all images read back empty, that is an image of the dimensions requested but only containing transparent black pixels. There are some possibly related issues on MoltenVK https://github.com/KhronosGroup/MoltenVK/issues/838, https://github.com/KhronosGroup/MoltenVK/issues/835, so the likely first step is to test a newer version of MoltenVK.
If rendering with Swiftshader, which only works for offscreen renders on MacOS due to #70, the readback works correctly and a valid image is produced. But if rendering with the hardware via MoltenVK, all images read back empty, that is an image of the dimensions requested but only containing transparent black pixels. There are some possibly related issues on MoltenVK https://github.com/KhronosGroup/MoltenVK/issues/838, https://github.com/KhronosGroup/MoltenVK/issues/835, so the likely first step is to test a newer version of MoltenVK.