From e82c5c660778b3805f50f3f2901923692c17db2a Mon Sep 17 00:00:00 2001
From: Jesse Yurkovich <deadpin>
Date: Sun, 18 Jul 2021 10:42:52 +1000
Subject: Fix T89868: Crash showing thumbnail of wide-aspect image

Scaling down images could create images with a width or height of zero.

Clamp at 1 to prevent a crash, also add an assert to scaling functions.

Ref D11956
---
 source/blender/editors/render/render_preview.c | 5 +++--
 source/blender/imbuf/intern/scaling.c          | 6 ++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/source/blender/editors/render/render_preview.c b/source/blender/editors/render/render_preview.c
index c7fa2a0ec87..5aa63ac56d8 100644
--- a/source/blender/editors/render/render_preview.c
+++ b/source/blender/editors/render/render_preview.c
@@ -1308,8 +1308,9 @@ static void icon_copy_rect(ImBuf *ibuf, uint w, uint h, uint *rect)
     scaledy = (float)h;
   }
 
-  ex = (short)scaledx;
-  ey = (short)scaledy;
+  /* Scaling down must never assign zero width/height, see: T89868. */
+  ex = MAX2(1, (short)scaledx);
+  ey = MAX2(1, (short)scaledy);
 
   dx = (w - ex) / 2;
   dy = (h - ey) / 2;
diff --git a/source/blender/imbuf/intern/scaling.c b/source/blender/imbuf/intern/scaling.c
index 757ec5f4b41..79c2583f983 100644
--- a/source/blender/imbuf/intern/scaling.c
+++ b/source/blender/imbuf/intern/scaling.c
@@ -1666,6 +1666,8 @@ static void scalefast_Z_ImBuf(ImBuf *ibuf, int newx, int newy)
  */
 bool IMB_scaleImBuf(struct ImBuf *ibuf, unsigned int newx, unsigned int newy)
 {
+  BLI_assert_msg(newx > 0 && newy > 0, "Images must be at least 1 on both dimensions!");
+
   if (ibuf == NULL) {
     return false;
   }
@@ -1712,6 +1714,8 @@ struct imbufRGBA {
  */
 bool IMB_scalefastImBuf(struct ImBuf *ibuf, unsigned int newx, unsigned int newy)
 {
+  BLI_assert_msg(newx > 0 && newy > 0, "Images must be at least 1 on both dimensions!");
+
   unsigned int *rect, *_newrect, *newrect;
   struct imbufRGBA *rectf, *_newrectf, *newrectf;
   int x, y;
@@ -1884,6 +1888,8 @@ static void *do_scale_thread(void *data_v)
 
 void IMB_scaleImBuf_threaded(ImBuf *ibuf, unsigned int newx, unsigned int newy)
 {
+  BLI_assert_msg(newx > 0 && newy > 0, "Images must be at least 1 on both dimensions!");
+
   ScaleTreadInitData init_data = {NULL};
 
   /* prepare initialization data */
-- 
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