add png_types.nim

nimPNG/png_types.nim

@@ -0,0 +1,14 @@
+type
+  PNGFilterStrategy* = enum
+    #every filter at zero
+    LFS_ZERO,
+    #Use filter that gives minimum sum, as described in the official PNG filter heuristic.
+    LFS_MINSUM,
+    #Use the filter type that gives smallest Shannon entropy for this scanLine. Depending
+    #on the image, this is better or worse than minsum.
+    LFS_ENTROPY,
+    #Brute-force-search PNG filters by compressing each filter for each scanLine.
+    #Experimental, very slow, and only rarely gives better compression than MINSUM.
+    LFS_BRUTE_FORCE,
+    #use predefined_filters buffer: you specify the filter type for each scanLine
+    LFS_PREDEFINED