iOS orientation change triggers MTL assertion

[OkanArikan]

While running the imgui-sapp sample on an iPhone (fips config sapp-metal-ios-xcode-debug), changing device orientation triggers a MTL assertion:

-[MTLDebugRenderCommandEncoder setScissorRect:]:3635: failed assertion `Set Scissor Rect Validation
(rect.y(0) + rect.height(480))(480) must be <= render pass height(320)

from function _sg_mtl_apply_scissor_rect, line [_sg.mtl.cmd_encoder setScissorRect:r];

[floooh]

Hmm yeah, I can also reproduce this on the simulator. The problem seems to be that the UIScreen.mainScreen.bounds property here doesn't flip x and y when the device is rotated, while the underlying view framebuffer appears to flip dimensions (otherwise that error message from the Metal validation layer wouldn't happen):

sokol/sokol_app.h

Line 3938 in e8931e4

CGRect screen_rect = UIScreen.mainScreen.bounds;

I need to come up with a different way to query the display dimensions I guess. Currently I'm deep into updating the dormant WebGPU code though.

[OkanArikan]

Perhaps the other way around (UIScreen.mainScreen.bounds correct but the drawable is not resized)? Removing

sokol/sokol_app.h

Line 4033 in e8931e4

_sapp.ios.view.autoResizeDrawable = false;

seems to fix the issue (let the iOS resize the drawable).

imgui-sapp and imgui-hidpi-sapp seem to work fine after that line is removed.

You have a comment above it and I did not have enough context. Happy to send you a PR if you think this is correct.

[floooh]

Hmm, I had to switch off autoResizeDrawable because it didn't honor the contentScaleFactor (as is mentioned in the comment above), I'll need to check if that's still the case in recent iOS versions.

[floooh]

Note: moving this ticket over to the sokol repository.

[floooh]

Ok, I now have both autoResizeEnabled on the MTKView, and explicitely set the view size in _sapp_ios_update_dimensions(). This seems to be the only way to "make it work" despite not making much sense.

It's yet another argument to scrap MTKView and insteas use CAMetalLayer directly though ;)

[OkanArikan]

Thank you for looking into this.

[floooh]

@OkanArikan: unfortunately this fix triggers a Metal validation layer error now (at least in the simulator, haven't checked on device yet), see #726.

[floooh]

...it seems I can no longer reproduce the original issue of triggering that assertion when the device orientation changes (on an iOS iPhone12 simulator with Xcode 13.4.1). I have reverted this "fix" (e.g. autoResizeEnabled is now turned off again). This fixes both the validation layer warning while device rotation appears to work.