LibGfx: Move all image loaders and writers to a subdirectory

Userland/Libraries/LibGfx/ImageFormats/PNGShared.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2022, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Array.h>
+#include <AK/SIMD.h>
+
+namespace Gfx::PNG {
+
+// https://www.w3.org/TR/PNG/#5PNG-file-signature
+static constexpr Array<u8, 8> header = { 0x89, 'P', 'N', 'G', 13, 10, 26, 10 };
+
+// https://www.w3.org/TR/PNG/#6Colour-values
+enum class ColorType : u8 {
+    Greyscale = 0,
+    Truecolor = 2, // RGB
+    IndexedColor = 3,
+    GreyscaleWithAlpha = 4,
+    TruecolorWithAlpha = 6,
+};
+
+// https://www.w3.org/TR/PNG/#9Filter-types
+enum class FilterType : u8 {
+    None,
+    Sub,
+    Up,
+    Average,
+    Paeth,
+};
+
+// https://www.w3.org/TR/PNG/#9Filter-type-4-Paeth
+ALWAYS_INLINE u8 paeth_predictor(u8 a, u8 b, u8 c)
+{
+    int p = a + b - c;
+    int pa = AK::abs(p - a);
+    int pb = AK::abs(p - b);
+    int pc = AK::abs(p - c);
+    if (pa <= pb && pa <= pc)
+        return a;
+    if (pb <= pc)
+        return b;
+    return c;
+}
+
+ALWAYS_INLINE AK::SIMD::u8x4 paeth_predictor(AK::SIMD::u8x4 a, AK::SIMD::u8x4 b, AK::SIMD::u8x4 c)
+{
+    return AK::SIMD::u8x4 {
+        paeth_predictor(a[0], b[0], c[0]),
+        paeth_predictor(a[1], b[1], c[1]),
+        paeth_predictor(a[2], b[2], c[2]),
+        paeth_predictor(a[3], b[3], c[3]),
+    };
+}
+
+};