Document System.Drawing OutOfMemoryException to ExternalException breaking change for .NET 10 with C# and VB examples

docs/core/compatibility/10.0.md

@@ -44,6 +44,7 @@ If you're migrating an app to .NET 10, the breaking changes listed here might af
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docs/core/compatibility/core-libraries/10.0/system-drawing-outofmemory-externalexception.md

@@ -0,0 +1,61 @@
+---
+title: "Breaking change: System.Drawing OutOfMemoryException changed to ExternalException"
+description: "Learn about the breaking change in .NET 10 where System.Drawing GDI+ OutOfMemory errors now throw ExternalException instead of OutOfMemoryException."
+ms.date: 08/15/2025
+ai-usage: ai-assisted
+---
+
+# System.Drawing OutOfMemoryException changed to ExternalException
+
+GDI+ error handling in System.Drawing has been updated to throw <xref:System.Runtime.InteropServices.ExternalException> instead of <xref:System.OutOfMemoryException> for `Status.OutOfMemory` errors.
+
+## Version introduced
+
+.NET 10 Preview 5
+
+## Previous behavior
+
+When GDI+ encountered `Status.OutOfMemory` errors (often due to invalid input rather than actual memory issues), System.Drawing APIs threw <xref:System.OutOfMemoryException>.
+
+## New behavior
+
+When GDI+ encounters `Status.OutOfMemory` errors, System.Drawing APIs now throw <xref:System.Runtime.InteropServices.ExternalException> instead.
+
+## Type of breaking change
+
+This is a [behavioral change](../../categories.md#behavioral-change).
+
+## Reason for change
+
+GDI+ isn't particularly good at returning errors when it's unable to create internal objects. There are many cases where object creation fails due to invalid input, and higher-level code gets a null and turns it into `Status.OutOfMemory`. This is frequently a source of confusion since the error is often not related to actual memory issues.
+
+The change to `ExternalException` provides more accurate error reporting, as this exception type is already thrown in other System.Drawing code paths for similar GDI+ errors.
+
+## Recommended action
+
+If your code catches `OutOfMemoryException` when using System.Drawing APIs, ensure you also catch `ExternalException` to handle these GDI+ errors.
+
+```csharp
+try
+{
+    // System.Drawing operations
+}
+catch (ExternalException ex)
+{
+    // Handle GDI+ errors (including former OutOfMemoryException cases)
+}
+catch (OutOfMemoryException ex)
+{
+    // Handle actual memory issues
+}
+```
+
+## Affected APIs
+
+All System.Drawing APIs that interact with GDI+ and previously could throw `OutOfMemoryException` for `Status.OutOfMemory` errors, including but not limited to:
+
+- <xref:System.Drawing.Bitmap?displayProperty=fullName> constructors and methods
+- <xref:System.Drawing.Graphics?displayProperty=fullName> methods
+- <xref:System.Drawing.Image?displayProperty=fullName> methods
+- <xref:System.Drawing.Icon?displayProperty=fullName> constructors and methods
+- Other System.Drawing types that use GDI+ internally

docs/core/compatibility/toc.yml

@@ -54,6 +54,8 @@ items:
                 href: core-libraries/10.0/sigterm-signal-handler.md
               - name: System.Linq.AsyncEnumerable included in core libraries
                 href: core-libraries/10.0/asyncenumerable.md
+              - name: System.Drawing OutOfMemoryException changed to ExternalException
+                href: core-libraries/10.0/system-drawing-outofmemory-externalexception.md
               - name: YMM embedded rounding removed from AVX10.2
                 href: core-libraries/10.0/ymm-embedded-rounding.md
           - name: Cryptography