From 1743ac47348ad82b00d476858e9c7aa4dc8554e6 Mon Sep 17 00:00:00 2001
From: Nathaniel Quillin <github@nathanielquillin.com>
Date: Mon, 20 Jul 2020 23:49:32 -0700
Subject: [PATCH] Initialize offset memory for PyImagingPhotoPut.

When using image mode "1" or "L" block.offset[3] is never initialized. In some use cases the block is passed to Tk_PhotoPutBlock (https://github.com/tcltk/tk/blob/master/generic/tkImgPhoto.c#L2752) and block.offset[3] is stored in alphaoffset which is later referenced.
---
 src/Tk/tkImaging.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Tk/tkImaging.c b/src/Tk/tkImaging.c
index 161a835fbd2..aca84523cb8 100644
--- a/src/Tk/tkImaging.c
+++ b/src/Tk/tkImaging.c
@@ -114,7 +114,7 @@ PyImagingPhotoPut(ClientData clientdata, Tcl_Interp* interp,
 
     if (strcmp(im->mode, "1") == 0 || strcmp(im->mode, "L") == 0) {
         block.pixelSize = 1;
-        block.offset[0] = block.offset[1] = block.offset[2] = 0;
+        block.offset[0] = block.offset[1] = block.offset[2] = block.offset[3] = 0;
     } else if (strncmp(im->mode, "RGB", 3) == 0) {
         block.pixelSize = 4;
         block.offset[0] = 0;