Crash when buffer is empty / SwiftUI

[matts9000]

macOS Version(s) Used to Build

macOS 13 Ventura

Xcode Version(s)

Xcode 14

Description

Hello,

I experience crashes with invalid NIL in the following function of Renderer.swift:

func selectBuffers(width: CGFloat) -> (MTLBuffer, MTLBuffer) {
    var level = 0
    for (minBuffer, maxBuffer) in zip(minBuffers, maxBuffers) {
        if CGFloat(minBuffer.length / MemoryLayout<Float>.size) < width {
            return (minBuffer, maxBuffer)
        }
        level += 1
    }

    **return (minBuffers.last!, maxBuffers.last!)**
}

I tried to reproduce this in debug mode, but I does not happen there - it happens only with the app compiled for run.
What I see is that in debug the drawing is much slower. So what I suspect is, that as I'm using SwiftUI redraws happen with empty buffers, which cause this.

BTW: thanks for this wonderful implementation of a waveform drawer!

Crash Logs, Screenshots or Other Attachments (if applicable)

No response

[atomhax]

I'm not sure if it's helpful but here is a partial crash log confirming this issue. As you mentioned it's only in the wild when built for release. However it's only happening for 1 of my testers.

Thread 0 name:
Thread 0 Crashed:
0   sotomata                      	0x00000001001c0a78 Swift runtime failure: Unexpectedly found nil while unwrapping an Optional value + 0 (<compiler-generated>:0)
1   sotomata                      	0x00000001001c0a78 Renderer.selectBuffers(width:) + 916 (Renderer.swift:76)
2   sotomata                      	0x00000001001c0bc4 Renderer.encode(to:pass:width:) + 220 (Renderer.swift:89)
3   sotomata                      	0x00000001001c0fcc Renderer.draw(in:) + 456 (Renderer.swift:128)
4   sotomata                      	0x00000001001c10b8 @objc Renderer.draw(in:) + 52 (<compiler-generated>:0)
5   MetalKit                      	0x00000001ed4dc050 -[MTKView draw] + 160 (MTKView.m:1376)
6   QuartzCore                    	0x0000000188c106f8 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 412 (CALayer.mm:2521)
7   QuartzCore                    	0x0000000188c21a1c CA::Context::commit_transaction(CA::Transaction*, double, double*) + 444 (CAContextInternal.mm:2714)
8   QuartzCore                    	0x0000000188c50ff4 CA::Transaction::commit() + 648 (CATransactionInternal.mm:432)
9   QuartzCore                    	0x0000000188c3af3c CA::Transaction::flush_as_runloop_observer(bool) + 88 (CATransactionInternal.mm:940)
10  UIKitCore                     	0x0000000189c3bc04 _UIApplicationFlushCATransaction + 52 (UIApplication.m:3286)
11  UIKitCore                     	0x0000000189d8c4b0 _UIUpdateSequenceRun + 84 (_UIUpdateSequence.mm:114)
12  UIKitCore                     	0x000000018a3f0c8c schedulerStepScheduledMainSection + 144 (_UIUpdateScheduler.m:1015)
13  UIKitCore                     	0x000000018a3f01e8 runloopSourceCallback + 92 (_UIUpdateScheduler.m:1164)
14  CoreFoundation                	0x00000001877a2128 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 28 (CFRunLoop.c:1957)
15  CoreFoundation                	0x00000001877ae7b4 __CFRunLoopDoSource0 + 176 (CFRunLoop.c:2001)
16  CoreFoundation                	0x00000001877335e8 __CFRunLoopDoSources0 + 244 (CFRunLoop.c:2038)
17  CoreFoundation                	0x00000001877490d4 __CFRunLoopRun + 828 (CFRunLoop.c:2953)
18  CoreFoundation                	0x000000018774e3ec CFRunLoopRunSpecific + 612 (CFRunLoop.c:3418)
19  GraphicsServices              	0x00000001c2beb35c GSEventRunModal + 164 (GSEvent.c:2196)
20  UIKitCore                     	0x0000000189adb6e8 -[UIApplication _run] + 888 (UIApplication.m:3782)
21  UIKitCore                     	0x0000000189adb34c UIApplicationMain + 340 (UIApplication.m:5372)
22  SwiftUI                       	0x000000018b11f41c closure #1 in KitRendererCommon(_:) + 176 (UIKitApp.swift:37)
23  SwiftUI                       	0x000000018b0859bc runApp<A>(_:) + 152 (UIKitApp.swift:14)
24  SwiftUI                       	0x000000018b06fa64 static App.main() + 128 (App.swift:114)
25  sotomata                      	0x000000010001fb24 static MyApp.$main() + 24 (sotomataApp.swift:10)
26  sotomata                      	0x000000010001fb24 main + 36 (RecordingsView.swift:0)
27  dyld                          	0x00000001a6c26dec start + 2220 (dyldMain.cpp:1165)

[atomhax]

I think this PR may fix the issue. Please review and let me know.