1 files changed, 17 insertions, 0 deletions
diff --git a/Userland/Libraries/LibGfx/PNGShared.h b/Userland/Libraries/LibGfx/PNGShared.h
index 3486456f86..6f60d848ae 100644
--- a/Userland/Libraries/LibGfx/PNGShared.h
+++ b/Userland/Libraries/LibGfx/PNGShared.h
@@ -8,6 +8,9 @@
 
 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,
@@ -26,4 +29,18 @@ enum class FilterType : u8 {
     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 = abs(p - a);
+    int pb = abs(p - b);
+    int pc = abs(p - c);
+    if (pa <= pb && pa <= pc)
+        return a;
+    if (pb <= pc)
+        return b;
+    return c;
+}
+
 };