From 6018731c1867c52a01e291613e95f6a3835a3f79 Mon Sep 17 00:00:00 2001 From: giraffedata Date: Wed, 23 Jan 2019 02:46:27 +0000 Subject: add comment git-svn-id: http://svn.code.sf.net/p/netpbm/code/trunk@3517 9d0c8265-081b-0410-96cb-a4ca84ce46f8 --- converter/other/pngx.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/converter/other/pngx.c b/converter/other/pngx.c index dfc74485..b96857e9 100644 --- a/converter/other/pngx.c +++ b/converter/other/pngx.c @@ -467,6 +467,15 @@ pngx_setIhdr(struct pngx * const pngxP, void pngx_setInterlaceHandling(struct pngx * const pngxP) { + /* It isn't clear what this does. The documentation is contradictory, + saying in some places that it gets the number of passes required. and + in others that it sets the interlacing scheme. In practice, whether + the compressor generates an interlaced image or not appears to be + controlled by png_set_IHDR and unaffected by this. + + Also, documentation says this returns 7 if the compressor is + interlacing, but it always returns 1 in practice. + */ pngxP->numPassesRequired = png_set_interlace_handling(pngxP->png_ptr); } -- cgit 1.4.1