test(video): add dmg-acid2 PPU rendering conformance test

tests/GameBoy.Core.Tests/DmgAcid2Tests.cs

@@ -0,0 +1,55 @@
+using GameBoy.Util;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace GameBoy.Tests
+{
+    public sealed class DmgAcid2Tests
+    {
+        private readonly ITestOutputHelper output;
+
+        public DmgAcid2Tests(ITestOutputHelper output)
+        {
+            this.output = output;
+        }
+
+        [Fact]
+        public void Acid2_FramebufferMatchesReference()
+        {
+            var emulator = new Emulator(TestRoms.Load("dmg-acid2.gb"));
+            for (int frame = 0; frame < 200; frame++)
+                emulator.RunFrame();
+
+            DecodedImage reference = PngImage.Decode(TestRoms.Path("dmg-acid2-ref.png"));
+            Assert.Equal(Emulator.ScreenWidth, reference.Width);
+            Assert.Equal(Emulator.ScreenHeight, reference.Height);
+
+            byte[] actual = emulator.Framebuffer;
+            int mismatches = 0;
+            int firstX = -1, firstY = -1;
+            for (int y = 0; y < reference.Height; y++)
+            {
+                for (int x = 0; x < reference.Width; x++)
+                {
+                    int index = y * reference.Width + x;
+                    int expectedShade = 3 - reference.Samples[index];
+                    if (actual[index] != expectedShade)
+                    {
+                        if (mismatches == 0)
+                        {
+                            firstX = x;
+                            firstY = y;
+                        }
+                        mismatches++;
+                    }
+                }
+            }
+
+            output.WriteLine($"mismatched pixels: {mismatches} / {reference.Width * reference.Height}");
+            if (mismatches > 0)
+                output.WriteLine($"first mismatch at ({firstX},{firstY})");
+
+            Assert.Equal(0, mismatches);
+        }
+    }
+}