use compression level 8 when writing png thumbnails (#505)

by default imlib2 uses a compression level of 2 for writing
pngs, which is rather low.

a compression level of 8 should result in slightly lower
thumbnail filesizes without affecting the encoding speed too
much (since these thumbnails are very small already).

Reviewed-on: https://codeberg.org/nsxiv/nsxiv/pulls/505
Reviewed-by: eylles <eylles@noreply.codeberg.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/thumbs.c b/thumbs.c
index f55a152..159aad7 100644
--- a/thumbs.c
+++ b/thumbs.c
@@ -121,6 +121,7 @@ static void tns_cache_write(tns_t *tns, Imlib_Image im, const char *filepath, bo
 			imlib_context_set_image(im);
 			if (imlib_image_has_alpha()) {
 				imlib_image_set_format("png");
+				imlib_image_attach_data_value("compression", NULL, 8, NULL);
 			} else {
 				imlib_image_set_format("jpg");
 				imlib_image_attach_data_value("quality", NULL, 90, NULL);