Implement movie mask transition opcode

2026-07-29 16:01:00 -04:00
parent 12af952b77
commit 3378abdeca
18 changed files with 573 additions and 45 deletions
--- a/engine/Age.Engine/Sys4/MovieMaskSurface.cs
+++ b/engine/Age.Engine/Sys4/MovieMaskSurface.cs
@@ -0,0 +1,66 @@
+using Age.Engine.Model;
+
+namespace Age.Engine.Sys4;
+
+/// <summary>Platform-neutral pixel oracle for opcode 0x24d's type-1 movie transition.</summary>
+public static class MovieMaskSurface
+{
+    /// <summary>Extract logical top-down green samples into the requested native mask dimensions.
+    /// Missing source pixels retain <paramref name="fill"/>.</summary>
+    public static byte[] ExtractGreen(RgbaImage frame, int width, int height, byte fill)
+    {
+        int safeWidth = System.Math.Max(0, width);
+        int safeHeight = System.Math.Max(0, height);
+        var mask = new byte[checked(safeWidth * safeHeight)];
+        if (fill != 0) System.Array.Fill(mask, fill);
+        int copyWidth = System.Math.Min(safeWidth, frame.Width);
+        int copyHeight = System.Math.Min(safeHeight, frame.Height);
+        for (int row = 0; row < copyHeight; row++)
+        {
+            int source = checked(row * frame.Width * 4 + 1);
+            int destination = checked(row * safeWidth);
+            for (int column = 0; column < copyWidth; column++, source += 4)
+                mask[destination + column] = frame.Pixels[source];
+        }
+        return mask;
+    }
+
+    /// <summary>Apply AGE's exact packed-ARGB multiplication to a captured RGBA surface. RGB and
+    /// pixels outside the requested rectangle are preserved. The multiplication deliberately includes
+    /// carry from the packed red/green bytes; it is not conventional alpha*mask/255.</summary>
+    public static RgbaImage Apply(
+        RgbaImage captured, ReadOnlySpan<byte> mask, int maskWidth, int maskHeight, int x, int y)
+    {
+        if (maskWidth < 0 || maskHeight < 0
+            || mask.Length != checked(maskWidth * maskHeight))
+            throw new System.ArgumentException("mask dimensions do not match its byte count", nameof(mask));
+        var output = new RgbaImage(
+            captured.Width, captured.Height, (byte[])captured.Pixels.Clone());
+        long left = System.Math.Max(0L, x);
+        long top = System.Math.Max(0L, y);
+        long right = System.Math.Min((long)captured.Width, (long)x + maskWidth);
+        long bottom = System.Math.Min((long)captured.Height, (long)y + maskHeight);
+        if (right <= left || bottom <= top) return output;
+
+        for (int destinationY = (int)top; destinationY < (int)bottom; destinationY++)
+        {
+            int maskY = destinationY - y;
+            for (int destinationX = (int)left; destinationX < (int)right; destinationX++)
+            {
+                int pixel = checked((destinationY * captured.Width + destinationX) * 4);
+                byte red = captured.Pixels[pixel];
+                byte green = captured.Pixels[pixel + 1];
+                byte blue = captured.Pixels[pixel + 2];
+                byte alpha = captured.Pixels[pixel + 3];
+                uint argb = (uint)alpha << 24
+                            | (uint)red << 16
+                            | (uint)green << 8
+                            | blue;
+                uint product = unchecked((argb >> 8)
+                    * mask[checked(maskY * maskWidth + destinationX - x)]);
+                output.Pixels[pixel + 3] = (byte)(product >> 24);
+            }
+        }
+        return output;
+    }
+}