Initial release

Sources/KnotchyCore/Stream/FrameSampler.swift

@@ -0,0 +1,22 @@
+/// Tells a blank frame from one with page content.
+public enum FrameSampler {
+    public static let grid = 48
+    public static let maxDimension = 1 << 15
+    public static let maxBytesPerRow = 1 << 20
+
+    /// Malformed input counts as uniform so it can never pose as content; the caps prevent overflow.
+    public static func isUniform(_ pixels: UnsafeRawBufferPointer, width: Int, height: Int, bytesPerRow: Int) -> Bool {
+        guard (1...maxDimension).contains(width), (1...maxDimension).contains(height),
+              bytesPerRow >= width * 4, bytesPerRow <= maxBytesPerRow,
+              pixels.count >= (height - 1) * bytesPerRow + width * 4
+        else { return true }
+        let first = pixels.loadUnaligned(fromByteOffset: 0, as: UInt32.self)
+        for gy in 0..<grid {
+            for gx in 0..<grid {
+                let offset = (gy * height / grid) * bytesPerRow + (gx * width / grid) * 4
+                if pixels.loadUnaligned(fromByteOffset: offset, as: UInt32.self) != first { return false }
+            }
+        }
+        return true
+    }
+}