feat: pause Metal renderer and graph when app is in background

VoidLink/ImGuiRenderer.mm

@@ -128,6 +128,12 @@
 - (void)drawInMTKView:(MTKView *)view
 {
 #if !defined(IMGUI_DISABLE)
+    // Don't render if app is in background to avoid GPU submission errors
+    // Allow rendering when inactive (control center, notifications)
+    if ([[UIApplication sharedApplication] applicationState] == UIApplicationStateBackground) {
+        return;
+    }
+    
     ImGuiIO &io = ImGui::GetIO();
     io.DisplaySize.x = view.bounds.size.width;
     io.DisplaySize.y = view.bounds.size.height;

VoidLink/Metal/MetalViewController.h

@@ -22,4 +22,7 @@
                             enableHdr:(BOOL)enableHdr
                        metricsHandler:(MetricsHandler _Nonnull)metricsHandler;
 
+- (void)pauseRendering;
+- (void)resumeRendering;
+
 @end

VoidLink/Metal/MetalViewController.m

@@ -91,6 +91,11 @@
 }
 
 - (void)waitToRenderTo:(nonnull CAMetalLayer *)layer {
+    // Skip waiting when renderer is paused
+    if (_renderer.isStopping) {
+        return;
+    }
+
     // Renderer obtains a nextDrawable, waiting if necessary
     if (@available(iOS 13.0, *)) {
         [_renderer waitToRenderTo:layer];
@@ -102,14 +107,20 @@
 
 /// Draw frame (used by manual loop)
 - (void)renderTo:(nonnull CAMetalLayer *)layer {
+    CFTimeInterval timeout = (1.0f / _framerate) - _renderer.averageGPUTime;
+    Frame *frame = [_frameQueue dequeueWithTimeout:timeout];
+
     if (!_renderer.isStopping) {
-        CFTimeInterval timeout = (1.0f / _framerate) - _renderer.averageGPUTime;
-        Frame *frame = [_frameQueue dequeueWithTimeout:timeout];
+        // Only render if not paused
         if (frame) {
             if (@available(iOS 13.0, *)) {
                 [_renderer renderFrame:frame toLayer:layer];
             }
         }
+    } else {
+        // When paused, we still dequeue frames to prevent accumulation
+        // but don't render them. Also sleep a bit to reduce CPU usage
+        usleep(100000);
     }
 }
 
@@ -117,6 +128,26 @@
     [_renderer drawableResize:size];
 }
 
+- (void)pauseRendering {
+    if (_displayLink) {
+        _displayLink.paused = YES;
+    }
+    if (_renderer) {
+        _renderer.isStopping = YES;
+    }
+    Log(LOG_I, @"[MetalViewController] Rendering paused");
+}
+
+- (void)resumeRendering {
+    if (_renderer) {
+        _renderer.isStopping = NO;
+    }
+    if (_displayLink) {
+        _displayLink.paused = NO;
+    }
+    Log(LOG_I, @"[MetalViewController] Rendering resumed");
+}
+
 - (void)viewDidDisappear:(BOOL)animated {
     [super viewDidDisappear:animated];
 

VoidLink/Stream/VideoDecoderRenderer.m

@@ -291,7 +291,9 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
                 // we missed a callback
                 // Log(LOG_W, @"*** slow frametime %.3f ms", frametime * 1000.0);
             }
-            [[ImGuiPlots sharedInstance] observeFloat:PLOT_FRAMETIME value:frametime * 1000.0];
+            if ([[UIApplication sharedApplication] applicationState] != UIApplicationStateBackground) {
+                [[ImGuiPlots sharedInstance] observeFloat:PLOT_FRAMETIME value:frametime * 1000.0];
+            }
         }
         lastTargetLocal = targetLocal;
 
@@ -843,11 +845,24 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
                             frameNumber:(int)frameNumber
                               frameType:(int)frameType
                         decodeStartTime:(CFTimeInterval)decodeStartTime {
-  if (frameType == FRAME_TYPE_IDR || _decompressionSession == nil) {
+  // Check if we need to create/recreate the decompression session
+  BOOL needsNewSession = (frameType == FRAME_TYPE_IDR || _decompressionSession == nil);
+
+  // Also check if the session might have been invalidated by iOS during background
+  if (!needsNewSession && _decompressionSession != nil) {
+    Boolean isValid = VTDecompressionSessionCanAcceptFormatDescription(_decompressionSession, _formatDesc);
+    if (!isValid) {
+      Log(LOG_W, @"Decompression session is invalid, needs recreation");
+      needsNewSession = YES;
+    }
+  }
+
+  if (needsNewSession) {
     [self setupDecompressionSession];
   }
 
   if (_decompressionSession == nil) {
+    Log(LOG_E, @"Failed to create decompression session");
     return kVTInvalidSessionErr;
   }
 
@@ -910,24 +925,26 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
               }
               int framesDropped = [self->_frameQueue enqueue:frame withSlackSize:3];
 
-              static PlotMetrics frameQueueMetrics = {};
-              [[ImGuiPlots sharedInstance] observeFloatReturnMetrics:PLOT_QUEUED_FRAMES value:[self->_frameQueue count] plotMetrics:&frameQueueMetrics];
-              [self safeCopyMetricsTo:&self->_frameQueueMetrics from:&frameQueueMetrics];
+              if ([[UIApplication sharedApplication] applicationState] != UIApplicationStateBackground) {
+                  static PlotMetrics frameQueueMetrics = {};
+                  [[ImGuiPlots sharedInstance] observeFloatReturnMetrics:PLOT_QUEUED_FRAMES value:[self->_frameQueue count] plotMetrics:&frameQueueMetrics];
+                  [self safeCopyMetricsTo:&self->_frameQueueMetrics from:&frameQueueMetrics];
 
-              [[ImGuiPlots sharedInstance] observeFloat:PLOT_DROPPED value:framesDropped];
+                  [[ImGuiPlots sharedInstance] observeFloat:PLOT_DROPPED value:framesDropped];
 
-              // It's important we capture host metrics on the incoming thread, as this frame object
-              // may have been dropped by the above enqueue
-              static CFTimeInterval lastHostFrame = 0.0f;
-              if (lastHostFrame != 0) {
-                [[ImGuiPlots sharedInstance] observeFloat:PLOT_HOST_FRAMETIME value:(frame.pts - lastHostFrame) * 1000.0];
+                  // It's important we capture host metrics on the incoming thread, as this frame object
+                  // may have been dropped by the above enqueue
+                  static CFTimeInterval lastHostFrame = 0.0f;
+                  if (lastHostFrame != 0) {
+                    [[ImGuiPlots sharedInstance] observeFloat:PLOT_HOST_FRAMETIME value:(frame.pts - lastHostFrame) * 1000.0];
+                  }
+                  lastHostFrame = frame.pts;
+
+                  // Decode time is not graphed because it is marked as hidden, but we can use the same mechanism for the value used by stats
+                  static PlotMetrics decodeMetrics = {};
+                  [[ImGuiPlots sharedInstance] observeFloatReturnMetrics:PLOT_DECODE value:(CACurrentMediaTime() - decodeStartTime) * 1000.0 plotMetrics:&decodeMetrics];
+                  [self safeCopyMetricsTo:&self->_decodeMetrics from:&decodeMetrics];
               }
-              lastHostFrame = frame.pts;
-
-              // Decode time is not graphed because it is marked as hidden, but we can use the same mechanism for the value used by stats
-              static PlotMetrics decodeMetrics = {};
-              [[ImGuiPlots sharedInstance] observeFloatReturnMetrics:PLOT_DECODE value:(CACurrentMediaTime() - decodeStartTime) * 1000.0 plotMetrics:&decodeMetrics];
-              [self safeCopyMetricsTo:&self->_decodeMetrics from:&decodeMetrics];
           });
       });
 

VoidLink/ViewControllers/StreamFrameViewController.m

@@ -1042,6 +1042,17 @@
         [self.pipController stopPictureInPicture];
     }
     
+    if ([_settings.renderingBackend intValue] == RENDER_METAL && self.metalViewController) {
+        Log(LOG_I, @"Resuming Metal renderer on foreground");
+        [self.metalViewController resumeRendering];
+    }
+    
+    if (self.imguiView && self.imguiView.mtkView && _settings.enableGraphs) {
+        self.imguiView.mtkView.enableSetNeedsDisplay = YES;
+        self.imguiView.mtkView.paused = NO;
+        Log(LOG_I, @"Resuming ImGui renderer on foreground");
+    }
+    
     [self->_streamMan.videoRenderer resetFramePacing];
     _isRestoringFromPiP = NO;
 }
@@ -1052,6 +1063,17 @@
     NSLog(@"did enter background, %d, %@, %d", _settings.enablePIP, self.pipController, self.pipController.isPictureInPictureActive);
     if (_settings.enablePIP && self.pipController && self.pipController.isPictureInPictureActive) {
         //Log(LOG_I, @"PIP is active, not terminating stream");
+    } else {
+        if ([_settings.renderingBackend intValue] == RENDER_METAL && self.metalViewController) {
+            Log(LOG_I, @"Pausing Metal renderer on background");
+            [self.metalViewController pauseRendering];
+        }
+        
+        if (self.imguiView && self.imguiView.mtkView) {
+            self.imguiView.mtkView.paused = YES;
+            self.imguiView.mtkView.enableSetNeedsDisplay = NO;
+            Log(LOG_I, @"Pausing ImGui renderer on background");
+        }
     }
 
     if (_inactivityTimer != nil) {