[Git][freetype/freetype-demos][gsoc-2022-chariri] * src/ftinspect/engine/engine.cpp: Fix crash on changing glyph index after

[Charlie Jiang (@cqjjjzr)]

Charlie Jiang pushed to branch gsoc-2022-chariri at FreeType / FreeType Demo Programs

Commits:

• 7a22072e
  by Charlie Jiang at 2022-07-08T02:03:14+08:00

  * src/ftinspect/engine/engine.cpp: Fix crash on changing glyph index after
  changing size quickly.
  
  When changing glyph index, the glyph name will be request by calling
  `Engine::glyphName`, which uses the cached `ftSize_`. However, `ftSize_` which
  is set by `FTC_Manager_LookupSize`, is not guaranteed to survive after other
  `FTC_ImageCache_LookupScaler` calls (called when the size changes).
  
  When one changes the size quickly (especially by Shift+MouseWheel), the object
  the old `ftSize_` points to is actually freed by `FTC_Manager_LookupSize`
  because the element count reachs the limit in the internal MRU caches.
  Therefore the `ftSize_` becomes a dangling pointer, causing crash when
  navigating to other glyphs.
  
  This bug was not so apparent before because one couldn't change the size so
  quickly, so memory allocating were maybe less frequent, and the dangling
  pointer still holds valid data. But more intense test still can reveal this.
  
  The solution here is simple, just lookup `ftSize_` again before fetching the
  glyph name.
  

1 changed file:

• src/ftinspect/engine/engine.cpp

Changes:

src/ftinspect/engine/engine.cpp

---

...	...	@@ -339,6 +339,9 @@ Engine::glyphName(int index)
339	339	if (index < 0)
340	340	throw std::runtime_error("Invalid glyph index");
341	341
	342	+ if (!FTC_Manager_LookupSize(cacheManager_, &scaler_, &ftSize_))
	343	+ return name;
	344	+
342	345	if (ftSize_ && FT_HAS_GLYPH_NAMES(ftSize_->face))
343	346	{
344	347	char buffer[256];

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