[
https://issues.apache.org/jira/browse/FOP-3141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17750385#comment-17750385
]
Jan Tošovský commented on FOP-3141:
-----------------------------------
I made some experiments and found the behavior of "fixed" is driven by
deliberate breaking out of the viewport in
[IFRenderer|https://github.com/apache/xmlgraphics-fop/blob/main/fop-core/src/main/java/org/apache/fop/render/intermediate/IFRenderer.java]:
{code:java}
//For FIXED, we need to break out of the current viewports to the
//one established by the page. We save the state stack for restoration
//after the block-container has been painted. See below.
List breakOutList = null;
if (bv.getPositioning() == Block.FIXED) {
breakOutList = breakOutOfStateStack();
}
AffineTransform positionTransform = new AffineTransform();
positionTransform.translate(bv.getXOffset(), bv.getYOffset());
{code}
{{bv.getYOffset()}} stores the desired "top" coordinate but that transformation
is not applied by that breakage. This handling is suspicious.
> <fo:block-container absolute-position="fixed"> - auto-calculating top/left
> positions based on bottom/right when height/width is provided
> ----------------------------------------------------------------------------------------------------------------------------------------
>
> Key: FOP-3141
> URL: https://issues.apache.org/jira/browse/FOP-3141
> Project: FOP
> Issue Type: Improvement
> Components: layout/block
> Affects Versions: 2.8
> Reporter: Jan Tošovský
> Priority: Minor
> Attachments: bottom.fo, bottom_absolute_fop.pdf,
> bottom_absolute_xep.pdf, bottom_auto_fop.pdf, bottom_auto_xep.pdf,
> bottom_current.pdf, bottom_expected.pdf, bottom_fixed_fop.pdf,
> bottom_fixed_xep.pdf
>
>
> When the block container is to be placed on the bottom edge, it is necessary
> to specify the top position even if the bottom and height attributes are
> specified (so the top position could be auto-calculated).
> I actually try generating some FO files originally designed for XEP, but for
> FOP I have to tweak all these top positions. It is straightforward, but I am
> losing the original semantics (top="18.8cm" instead of more clear bottom="0").
> I could locate the possible place for tweaking:
> [https://github.com/apache/xmlgraphics-fop/blob/main/fop-core/src/main/java/org/apache/fop/fo/properties/CommonRelativePosition.java]
> In the constructor, if the top is zero, but both the bottom and the height
> are non-zero, the top could be calculated. Same for the left and right +
> width).
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
