On Mon, Jun 2, 2014 at 8:32 PM, Robert O'Callahan <rob...@ocallahan.org>
wrote:
> On Tue, Jun 3, 2014 at 3:28 PM, Rik Cabanier <caban...@gmail.com> wrote:
>
>> Yes, isIdentity is used as an indication that nothing needs to be done or
>> that the transform hasn't changed.
>> Maybe we should rename it to isDefault, isInitial or isNoOp?
>>
>
> I think isIdentity is the right name.
>
> Glancing through Gecko I see places where we're able to entirely skip
> possibly-expensive transformation steps if we have an identity matrix, so I
> guess isIdentity is useful to have since even if we make
> multiplication-by-identity free, checking isIdentity might mean you can
> completely avoid traversing some application data structure.
>
Yes, that's what I'm seeing in WebKit and Blink as well.
For instance:
const AffineTransform transform = context->getCTM();
if (m_shadowsIgnoreTransforms && !transform.isIdentity()) {
FloatQuad transformedPolygon =
transform.mapQuad(FloatQuad(shadowedRect));
transformedPolygon.move(m_offset);
layerRect =
transform.inverse().mapQuad(transformedPolygon).boundingBox();
} else {
layerRect = shadowedRect;
layerRect.move(m_offset);
}
and:
if (!currentTransform.isIdentity()) {
FloatPoint3D absoluteAnchorPoint(anchorPoint());
absoluteAnchorPoint.scale(size().width(), size().height(), 1);
transform.translate3d(absoluteAnchorPoint.x(),
absoluteAnchorPoint.y(), absoluteAnchorPoint.z());
transform.multiply(currentTransform);
transform.translate3d(-absoluteAnchorPoint.x(),
-absoluteAnchorPoint.y(), -absoluteAnchorPoint.z());
}
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