290432 - Add push/pop translation functions to nsIRenderingContext

Status: RESOLVED FIXED

(Core Graveyard :: GFX, defect)

Description

[Robert O'Callahan (:roc) (email my personal email if necessary)]

In a couple of places frames need to save and restore the current translation in
the rendering context while they paint a child. We don't use PushState/PopState
because those do a lot more work than we really need to do. We can't just apply
a negative translation at the end because roundoff errors can accumulate.
Instead we save and restore part of the translation matrix. This causes problems
for Cairo since Cairo doesn't have a translation matrix; what actually happens
is that it conses up a fake one, and when frames poke the translation matrix to
restore the old translation, that has no effect.

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix

This just moves the save and restore code behind virtual functions in
nsIRenderingContext so that I can override them to do something else in
nsCairoRenderingContext.

Comment 2

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 180776 [details] [diff] [review]
fix

>Index: gfx/public/nsIRenderingContext.h

>+  struct PushedTranslation {
>+    float mSavedX, mSavedY;
>+  };
>+  NS_IMETHOD PushTranslation(PushedTranslation* aState) = 0;
>+
>+  NS_IMETHOD PopTranslation(PushedTranslation* aState) = 0;

Is there a reason to have PopTranslation called manually instead of having the
PushedTranslation destructor pop?  The latter can't be forgotten and all...

>Index: gfx/src/shared/nsRenderingContextImpl.cpp

> nsRenderingContextImpl::PushTranslation(PushedTranslation* aState)

NS_PRECONDITION(aState, ...)

> nsRenderingContextImpl::PopTranslation(PushedTranslation* aState)

NS_PRECONDITION(aState, ....)

r+sr=bzbarsky, with either approach on popping...

Comment 3

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix #2

OK, here's the patch with an auto-object to do the popping.

Comment 4

[Boris Zbarsky [:bzbarsky]]

Comment on attachment 181100 [details] [diff] [review]
fix #2

Looks good.

Comment 5

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Comment on attachment 181100 [details] [diff] [review]
fix #2

Modest code refactoring that should have no effect on the regular builds but is
needed for Cairo Gfx to work.

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

*** Bug 290903 has been marked as a duplicate of this bug. ***

Comment 7

[Asa Dotzler [:asa]]

Comment on attachment 181100 [details] [diff] [review]
fix #2

a=asa

Comment 8

[Robert O'Callahan (:roc) (email my personal email if necessary)]

checked in