Fix unhandled ArgumentOutOfRangeException when exporting FlameGraph with unrendered canvas

src/PerfView.Tests/StackViewer/StackWindowTests.cs

@@ -859,5 +859,39 @@ public override string GetFrameName(StackSourceFrameIndex frameIndex, bool verbo
                 return frameIndex.ToString();
             }
         }
+
+        [WpfFact]
+        [WorkItem(2308, "https://github.com/Microsoft/perfview/issues/2308")]
+        public void TestExportFlameGraphWithInvalidCanvasSize()
+        {
+            // Create a canvas with zero size (simulating an unrendered or collapsed canvas)
+            var canvas = new Canvas();
+            canvas.Width = 0;
+            canvas.Height = 0;
+            canvas.Measure(new Size(0, 0));
+            canvas.Arrange(new Rect(0, 0, 0, 0));
+
+            var tempFile = Path.GetTempFileName();
+            try
+            {
+                // Attempt to export should throw InvalidOperationException with a meaningful message
+                var exception = Assert.Throws<InvalidOperationException>(() =>
+                {
+                    FlameGraph.Export(canvas, tempFile);
+                });
+
+                // Verify the exception message is helpful
+                Assert.Contains("canvas has an invalid size", exception.Message);
+                Assert.Contains("width=0", exception.Message);
+                Assert.Contains("height=0", exception.Message);
+            }
+            finally
+            {
+                if (File.Exists(tempFile))
+                {
+                    File.Delete(tempFile);
+                }
+            }
+        }
     }
 }

src/PerfView/StackViewer/FlameGraph.cs

@@ -83,7 +83,18 @@ public static IEnumerable<FlameBox> Calculate(CallTree callTree, double maxWidth
         public static void Export(Canvas flameGraphCanvas, string filePath)
         {
             var rectangle = new Rect(flameGraphCanvas.RenderSize);
-            var renderTargetBitmap = new RenderTargetBitmap((int)rectangle.Right, (int)rectangle.Bottom, 96d, 96d, PixelFormats.Default);
+            int width = (int)rectangle.Right;
+            int height = (int)rectangle.Bottom;
+
+            // Validate that the canvas has a valid size before attempting to export
+            if (width <= 0 || height <= 0)
+            {
+                throw new InvalidOperationException(
+                    $"Cannot export flame graph: the canvas has an invalid size (width={width}, height={height}). " +
+                    "Please ensure the flame graph is visible and has been rendered before attempting to export.");
+            }
+
+            var renderTargetBitmap = new RenderTargetBitmap(width, height, 96d, 96d, PixelFormats.Default);
             renderTargetBitmap.Render(flameGraphCanvas);
 
             var pngEncoder = new PngBitmapEncoder();

src/PerfView/StackViewer/StackWindow.xaml.cs

@@ -2764,10 +2764,18 @@ private void DoSaveFlameGraph(object sender, RoutedEventArgs e)
             var result = saveDialog.ShowDialog();
             if (result == true)
             {
-                if (FlameGraphCanvas.IsEmpty || m_RedrawFlameGraphWhenItBecomesVisible)
-                    RedrawFlameGraph();
+                try
+                {
+                    if (FlameGraphCanvas.IsEmpty || m_RedrawFlameGraphWhenItBecomesVisible)
+                        RedrawFlameGraph();
 
-                FlameGraph.Export(FlameGraphCanvas, saveDialog.FileName);
+                    FlameGraph.Export(FlameGraphCanvas, saveDialog.FileName);
+                    StatusBar.Log($"Saved flame graph to {saveDialog.FileName}");
+                }
+                catch (InvalidOperationException ex)
+                {
+                    StatusBar.LogError($"Failed to save flame graph: {ex.Message}");
+                }
             }
         }