Complete native numbered-save round trips

engine/Age.Engine.Tests/RetainedSurfaceRasterizerTests.cs

@@ -0,0 +1,41 @@
+using Age.Engine.Model;
+using Age.Engine.Sys4;
+
+public class RetainedSurfaceRasterizerTests
+{
+    [Fact]
+    public void CompositeRangePublishesScaledRetainedTextureIntoOffscreenSurface()
+    {
+        var gfx = new GfxState();
+        gfx.SetSurface(2, 0x1234, -1);
+        gfx.BindDraw(100, 2, 0, 0, 4, 4, 0, 0);
+        gfx.SetCurrentScale(100, (50, 50, 100));
+        gfx.SetSurface(3, 0x5678, -1);
+        gfx.BindDraw(200, 3, 0, 0, 2, 2, 0, 0);
+
+        byte[] sourcePixels = new byte[4 * 4 * 4];
+        for (int index = 0; index < sourcePixels.Length; index += 4)
+        {
+            sourcePixels[index] = 0x44;
+            sourcePixels[index + 1] = 0x88;
+            sourcePixels[index + 2] = 0xcc;
+            sourcePixels[index + 3] = 0xff;
+        }
+        var source = new RgbaImage(4, 4, sourcePixels);
+        var excluded = new RgbaImage(2, 2, Enumerable.Repeat((byte)0xff, 16).ToArray());
+        var destination = new RgbaImage(2, 2, new byte[16]);
+
+        int rendered = RetainedSurfaceRasterizer.CompositeRange(
+            destination, gfx.SnapshotVisibleObjects(), 100, 1,
+            item => item.Handle == 100 ? source : excluded);
+
+        Assert.Equal(1, rendered);
+        for (int index = 0; index < destination.Pixels.Length; index += 4)
+        {
+            Assert.Equal(0x44, destination.Pixels[index]);
+            Assert.Equal(0x88, destination.Pixels[index + 1]);
+            Assert.Equal(0xcc, destination.Pixels[index + 2]);
+            Assert.Equal(0xff, destination.Pixels[index + 3]);
+        }
+    }
+}