mirror of
https://git.lyx.org/repos/lyx.git
synced 2024-11-30 05:12:40 +00:00
26eb5092fb
We already have a CoordCache of insets dimensions. It is not necessary to store the same information in two places. Give a name to CoordCache tables types to improve code readability. Remove ParagraphMetrics::singleWidth, which is not used anymore.
175 lines
6.4 KiB
Org Mode
175 lines
6.4 KiB
Org Mode
# -*- org -*-
|
|
Understanding the painting process
|
|
|
|
This file tries to describe the state of the metrics/painting
|
|
mechanism, and identify the improvements that could be made. The first
|
|
section can be read alone, although the context for them is really
|
|
given in the following ones.
|
|
|
|
Please keep this file up to date as the code evolves!!!
|
|
|
|
Abbreviations:
|
|
bv: BufferView
|
|
pm: ParagraphMetrics
|
|
tm::TextMetrics
|
|
|
|
* Questions / Ideas
|
|
|
|
These questions are consequences of the description made in the
|
|
following section. Some actions are proposed.
|
|
|
|
** SinglePar update
|
|
|
|
The flag Update::SinglePar is set in many places but never acted on.
|
|
Instead, metrics update is skipped whenever the recorded height of
|
|
current paragraph did not change and Update::Force was not specified.
|
|
Is it better to keep that (which incurs extra work) or to condition it
|
|
on Update::SinglePar? If the first solution is kept, the flag
|
|
SingleParUpdate shall be removed.
|
|
|
|
Moreover, I fail to see (yet) where the 'single' part of the program
|
|
is acted on.
|
|
|
|
** Buffer::change issues
|
|
|
|
When calling Buffer::changed outside of bv::processUpdateFlags,
|
|
how do we know that the update strategy is set correctly? It is
|
|
possible to reset the strategy at the end of bv::draw. What would be
|
|
a good value? NoScreenUpdate?
|
|
|
|
On a related note, what is the semantics of a call to
|
|
Buffer::changed(false)? What does the caller mean?
|
|
|
|
** How to avoid redraw with FitCursor when the cursor is already OK?
|
|
|
|
In this case, we invoke Buffer::change(false) with drawing disabled
|
|
and NoScreenUpdate strategy.
|
|
|
|
In the draw phase, bv::checkCursorScrollOffset (the horizontal
|
|
scrolling machinery) will change the strategy to FullScreenUpdate if
|
|
the current row needs further scrolling.
|
|
|
|
When the update strategy it kept to NoScreenUpdate, there is currently
|
|
a no-draw full repaint, which should not be necessary. It would be
|
|
possible to avoid that if the call to checkCursorScrollOffset was done
|
|
in bv::processUpdateFlags instead of bv::draw.
|
|
|
|
The global idea would be to extend FitCursor to cover also horizontal
|
|
cursor.
|
|
|
|
|
|
* Proposals
|
|
|
|
** set inset position during metrics phase
|
|
|
|
This implies to set inset positions relative to outer inset during
|
|
metrics phase and then in a second loop to descend into insets and
|
|
update positions correctly.
|
|
|
|
Effect: avoid going through the painter machinery when it is not necessary.
|
|
|
|
** Merging bv::updateMetrics and tm::metrics
|
|
|
|
While the full metrics computation tries hard to limit the number of
|
|
paragraphs that are rebroken, the version that is used for inner inset
|
|
does not try any such optimization. This can be very bad for very tall
|
|
insets. We should re-use the bv::updateMetrics logic: + transfer all the logic of bv::updateMetrics to tm.
|
|
+ Main InsetText should not be special.
|
|
|
|
** Metrics outside of visible area
|
|
|
|
Currently metrics are computed for current visible paet of text, the
|
|
page above and the page below. It should be possible to compute hidden
|
|
rows ony on demand, although it might be a bit slow.
|
|
|
|
There was a proposal to always compute _all_ rows, but this may become
|
|
expensive for large files. This would though help scrolling.
|
|
|
|
|
|
* Description of current drawing mechanism
|
|
|
|
** Two stage drawing
|
|
|
|
There are two parts to drawing the work area: + the metrics phase computes the size of insets and breaks the
|
|
paragraphs into rows. It stores the dimension of insets (both
|
|
normal and math) in bv::coordCache.
|
|
|
|
+ the drawing phase draws the contents and caches the inset
|
|
positions. Since the caching of positions is useful in itself,
|
|
there is a provision for drawing "without" drawing when the only
|
|
thing we want is to cache inset positions
|
|
(Painter::setDrawingEnabled).
|
|
|
|
The machinery is controlled via bv::processUpdateFlags. This method is
|
|
called at the end of bv::mouseEventDispatch and in
|
|
GuiApplication::dispatch, via the updateCurrentView method. There are
|
|
also several calls in code related to dialogs. We should evaluate
|
|
whether this is correct.
|
|
|
|
Depending on the Update::flags passed to the method, it sets an update
|
|
strategy in (NoScreenUpdate, SingleParUpdate, FullScreenUpdate,
|
|
DecorationUpdate). It triggers a recomputation of the metrics when either: + Update::Force has been specified
|
|
+ Update::FitCursor has been specified and there is a need to scroll
|
|
the display. + the current paragraph, after rebreak, does not have the same height as in
|
|
existing metrics. Note that the Update::SinglePar flag is *never*
|
|
taken into account.
|
|
|
|
The screen is drawn (with appropriate update strategy), except when
|
|
update flag is Update::None.
|
|
|
|
|
|
** Metrics computation
|
|
|
|
This is triggered by bv::updateMetrics, which calls tm::redoParagraph for
|
|
+ all visible paragraphs + paragraph above the screen (up to one page)
|
|
+ paragraphs below the screen (up to one page again)
|
|
|
|
The paragraphs outside of the screen are required to make PageUp/Down
|
|
work.
|
|
|
|
tm::redoParagraph will call Inset::metrics for each inset. In the case
|
|
of text insets, this will invoke recursively tm::metrics, which redoes
|
|
all the paragraphs of the inset.
|
|
|
|
|
|
** Drawing the work area.
|
|
|
|
This is done in bv::draw. This method is triggered mainly by
|
|
Buffer::changed, which draws all the work areas that show the given buffer.
|
|
|
|
Note that, When Buffer::changed is called outside of
|
|
bv::processUpdateFlags, it is not clear whether the update strategy
|
|
has been set to a reasonable value beforehand.
|
|
|
|
The action depends on the update strategy: + NoScreenUpdate: repaint the whole screen with drawing disabled.
|
|
This is only needed to update the inset positions. I am not sure
|
|
when this is necessary, actually. This is triggered when:
|
|
- Update::FitCursor is set but the cursor is already visible. It is
|
|
not clear why something needs to be done in this case, since this
|
|
should be equivalent to Update::None.
|
|
- this is also set when update flag is Update::None, but this value
|
|
is AFAICS not acted on in the code (meaning that nothing happens
|
|
at all in this case).
|
|
|
|
+ FullScreenUpdate: repaint the whole screen. This is set when:
|
|
- updateMetrics has been invoked.
|
|
- scroll value of current row has changed (although this should not
|
|
be necessary). + DecorationUpdate: actually like FullScreenUpdate, although it is
|
|
intended to only update inset decorations. This triggers when:
|
|
- Update::Decoration is set (without Update::Force) as flag.
|
|
- An hovered inset is detected.
|
|
|
|
+ SingleParUpdate: only tries to repaint current paragraph in a way
|
|
that is not yet very clear to me.
|