From 2a087df8fc709c67d69280206b609f2ec22babbb Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Tue, 2 Mar 2021 10:19:22 +0000
Subject: [PATCH] add some printf dbg

to linnsgif, trying to find the GIF decode bug
---
 libvips/foreign/libnsgif/libnsgif.c | 31 +++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/libvips/foreign/libnsgif/libnsgif.c b/libvips/foreign/libnsgif/libnsgif.c
index 5550a613..d8d5df19 100644
--- a/libvips/foreign/libnsgif/libnsgif.c
+++ b/libvips/foreign/libnsgif/libnsgif.c
@@ -571,6 +571,8 @@ static void gif__record_previous_frame(gif_animation *gif)
         const uint32_t *frame_data;
         uint32_t *prev_frame;
 
+	printf( "gif__record_previous_frame:\n" );
+
         if (gif->decoded_frame == GIF_INVALID_FRAME ||
             gif->decoded_frame == gif->prev_index) {
                 /* No frame to copy, or already have this frame recorded. */
@@ -613,6 +615,8 @@ static gif_result gif__recover_previous_frame(const gif_animation *gif)
         unsigned width  = gif->width  < gif->prev_width  ? gif->width  : gif->prev_width;
         uint32_t *frame_data;
 
+	printf( "gif__recover_previous_frame:\n" );
+
         if (prev_frame == NULL) {
                 return GIF_FRAME_DATA_ERROR;
         }
@@ -659,6 +663,31 @@ gif_internal_decode_frame(gif_animation *gif,
         unsigned int x, y, decode_y, burst_bytes;
         register unsigned char colour;
 
+	printf( "gif_internal_decode_frame: frame = %d, clear_image = %d\n",
+	     frame, clear_image );
+	printf( "gif->frames[frame].disposal_method == " );
+	switch( gif->frames[frame].disposal_method ) {
+	case 0:
+		printf( "NONE\n" );
+		break;
+
+	case GIF_FRAME_COMBINE:
+		printf( "COMBINE\n" );
+		break;
+
+	case GIF_FRAME_CLEAR:
+		printf( "CLEAR\n" );
+		break;
+
+	case GIF_FRAME_RESTORE:
+		printf( "RESTORE\n" );
+		break;
+
+	case GIF_FRAME_QUIRKS_RESTORE:
+		printf( "QUIRKS_RESTORE\n" );
+		break;
+	}
+
         /* Ensure this frame is supposed to be decoded */
         if (gif->frames[frame].display == false) {
                 return GIF_OK;
@@ -880,6 +909,7 @@ gif_internal_decode_frame(gif_animation *gif,
                 }
 
                 /* Decompress the data */
+		printf( "... decompressing frame data\n" );
                 for (y = 0; y < height; y++) {
                         if (interlace) {
                                 decode_y = gif_interlaced_line(height, y) + offset_y;
@@ -924,6 +954,7 @@ gif_internal_decode_frame(gif_animation *gif,
                         }
                 }
         } else {
+		printf( "... clearing frame\n" );
                 /* Clear our frame */
                 if (gif->frames[frame].disposal_method == GIF_FRAME_CLEAR) {
                         for (y = 0; y < height; y++) {