There are two callers of nsFilterInstance::PaintFilteredFrame:
1. nsSVGUtils::PaintFrameWithEffects at [1]
This function is used while painting a filtered element on a path which
display item painting is not supported yet, such as drawing elements inside a
indirect painted SVG object, such as a mask, a clipPath or a gradient object.
Let's say we have a masked element, which refers to an SVG mask, and there is
a filtered element inside that SVG mask.
Using nsFilterInstance::PaintFilteredFrame to paint that filtered frame in
the mask, we have to pass a gfxContext and a transform matrix to it. The
transform of the gfxContext 'target' that we pass in consists of a transform
from the referenced frame, of the masked frame, to the masked frame. We also
pass in a transform matrix 'aTransform', this matrix contains a transform
from the the masked frame to the filtered frame in *device units*, which
means it contains css-to-dev-px scaling factor.
2. nsSVGIntegrationUtils::PaintFilter at [2]
This function is used by normal display item painting.
The same, we pass a gfxContext 'context' and a transform matrix 'tm' into
nsFilterInstance::PaintFilteredFrame. The transform matrix of 'context'
consists of a transform from the referenced frame, of the filtered frame,
to this filtered frame, but the scale factor was taken out . The transform
matrix 'tm' we pass in contains scale transform from the referenced frame to
the filtered frame in *device unit*.
Inside nsFilterInstance::PaintFilteredFrame, we treat the transform matrix of
'aCtx' and 'aTransform' as parameters we pass in in #2 caller. So it can be
failed in #1. For example, if the filtered frame inside a masked frame has a
translation transform applied, since that translation was put in 'aTransfrom',
but we only use the scale factor of 'aTransform' in
nsFilterInstance::PaintFilteredFrame, translation factor disappears.
In this patch, I unified the definition of parameters of
nsFilterInstance::PaintFilteredFrame:
1. nsFilterInstance::PaintFilteredFrame(aCtx): the transform matrix of aCtx
should be a transform from the referenced frame to the filtered frame in
*css units*. Originally, the aCtx we passed in #1 is in device units, which
should be fixed; the aCtx we passed in #2 does not even include css scaling
factor, need be fixed too.
2. nsFilterInstance::PaintFilteredFrame(aTransform): this transform matrix
should contain only scaling factor in device units. And I removed it in the
end since I found we can get this value easily right inside the callee.
[1]
https://hg.mozilla.org/mozilla-central/file/ef585ac7c476/layout/svg/nsSVGUtils.cpp#l857
[2]
https://hg.mozilla.org/mozilla-central/file/ef585ac7c476/layout/svg/nsSVGIntegrationUtils.cpp#l1114
MozReview-Commit-ID: gRV128NyQv
--HG--
extra : rebase_source : 15d130babd07734c3c36e24e9ea8b5c4e5f7dbbf
7249e683c3