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LibPDF: Use a RAII object to restore state in recursive render

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Previously, if one operator returned an error, the TRY() would cause
us to return without restoring the outer graphics state, leading to
problems such as handing a 3-tuple to a grayscale color space
(because the inner object set up a grayscale color space that we
failed to dispose of).

Makes us crash later on page 43 of
https://devstreaming-cdn.apple.com/videos/wwdc/2017/821kjtggolzxsv/821/821_get_started_with_display_p3.pdf
This commit is contained in:
Nico Weber 2023-10-18 11:46:11 -04:00 committed by Tim Flynn
parent c58193bafa
commit b835d2bd66
Notes: sideshowbarker 2024-07-16 21:45:42 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/b835d2bd66
Pull-request: https://github.com/SerenityOS/serenity/pull/21489
1 changed files with 19 additions and 2 deletions
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21
Userland/Libraries/LibPDF/Renderer.cpp
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@ -644,7 +644,25 @@ RENDERER_HANDLER(paint_xobject)
return {};
}
MUST(handle_save_state({}));
// Use a RAII object to restore the graphics state, to make sure it gets restored even if
// a TRY(handle_operator()) causes us to exit the operators loop early.
class ScopedState {
public:
ScopedState(Renderer& renderer)
: m_renderer(renderer)
{
MUST(m_renderer.handle_save_state({}));
}
~ScopedState()
{
MUST(m_renderer.handle_restore_state({}));
}
private:
Renderer& m_renderer;
};
ScopedState scoped_state { *this };
Vector<Value> matrix;
if (xobject->dict()->contains(CommonNames::Matrix)) {
matrix = xobject->dict()->get_array(m_document, CommonNames::Matrix).value()->elements();
@ -655,7 +673,6 @@ RENDERER_HANDLER(paint_xobject)
auto operators = TRY(Parser::parse_operators(m_document, xobject->bytes()));
for (auto& op : operators)
TRY(handle_operator(op, xobject_resources));
MUST(handle_restore_state({}));
return {};
}