ImageSurface: Support memory pressure

src/Libs/cairo-1.0/Internal/SurfaceHandle.cs

@@ -1,9 +1,30 @@
-namespace Cairo.Internal;
+using System;
+
+namespace Cairo.Internal;
 
 public partial class SurfaceOwnedHandle
 {
+    private long _memoryPressure;
+
+    internal void AddMemoryPressure(long memoryPressure)
+    {
+        if (memoryPressure > 0)
+        {
+            _memoryPressure = memoryPressure;
+            GC.AddMemoryPressure(_memoryPressure);
+        }
+    }
+
+    private void RemoveMemoryPressure()
+    {
+        if (_memoryPressure > 0)
+            GC.RemoveMemoryPressure(_memoryPressure);
+    }
+
     protected override bool ReleaseHandle()
     {
+        RemoveMemoryPressure();
+
         Surface.Destroy(handle);
         return true;
     }

src/Libs/cairo-1.0/Public/ImageSurface.cs

@@ -7,20 +7,27 @@ public class ImageSurface : Surface
     public ImageSurface(Format format, int width, int height)
         : base(Internal.ImageSurface.Create(format, width, height))
     {
+        Handle.AddMemoryPressure(GetSizeInBytes());
     }
 
     public Format Format => Internal.ImageSurface.GetFormat(Handle);
     public int Height => Internal.ImageSurface.GetHeight(Handle);
     public int Width => Internal.ImageSurface.GetWidth(Handle);
+
+    /// <summary>
+    /// Number of bytes per row.
+    /// </summary>
     public int Stride => Internal.ImageSurface.GetStride(Handle);
 
+    private int GetSizeInBytes() => Stride * Height;
+
     public Span<byte> GetData()
     {
-        IntPtr data = Internal.ImageSurface.GetData(Handle);
-        int len = Stride * Height; // Stride is the number of bytes per row.
+        var data = Internal.ImageSurface.GetData(Handle);
+
         unsafe
         {
-            return new Span<byte>(data.ToPointer(), len);
+            return new Span<byte>(data.ToPointer(), GetSizeInBytes());
         }
     }
 }

src/Libs/cairo-1.0/Public/Surface.cs

@@ -47,7 +47,24 @@ public Surface CreateSimilar(Content content, int width, int height)
         => new Surface(Internal.Surface.CreateSimilar(Handle, content, width, height));
 
     public Surface CreateSimilarImage(Format format, int width, int height)
-        => new Surface(Internal.Surface.CreateSimilarImage(Handle, format, width, height));
+    {
+        var handle = Internal.Surface.CreateSimilarImage(Handle, format, width, height);
+
+        //See: https://www.cairographics.org/manual/cairo-Image-Surfaces.html#cairo-format-t
+        var bytesPerPixel = format switch
+        {
+            Format.A1 => 1 / 8d,
+            Format.A8 => 1,
+            Format.Argb32 => 4,
+            Format.Rgb24 => 4,
+            Format.Rgb30 => 4,
+            Format.Rgb16565 => 2,
+            _ => 0 //No memory pressure is applied
+        };
+        handle.AddMemoryPressure((long) (width * height * bytesPerPixel));
+
+        return new Surface(handle);
+    }
 
     public Surface CreateForRectangle(double x, double y, double width, double height)
         => new Surface(Internal.Surface.CreateForRectangle(Handle, x, y, width, height));