mirror of
https://git.lyx.org/repos/lyx.git
synced 2024-11-23 02:14:50 +00:00
192 lines
6.9 KiB
Org Mode
192 lines
6.9 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
|
|
|
|
This flag only has an effect in the current BufferView, but I think it
|
|
is useful in other views too. Doing this will require some work on the
|
|
update pipeline, though.
|
|
|
|
** 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.
|
|
|
|
|
|
* Clean-up of drawing code
|
|
|
|
** Set Row::changed() in a finer way
|
|
|
|
*** singleParUpdate
|
|
|
|
When the height of the current paragraph changes, there is no need for
|
|
a full screen update. Only the rows after the current one need to have
|
|
their position recomputed.
|
|
|
|
This is also true when scrolling (how to do that?)
|
|
|
|
*** redoParagraph
|
|
|
|
It should be possible to check whether the new row is the same as the
|
|
old one and keep its changed() status in this case. This would reduce
|
|
a lot the amount of stuff to redraw.
|
|
|
|
** Put labels and friends in the Row as elements
|
|
|
|
It should not be necessary to access the Paragraph object to draw.
|
|
Adding the static elements to Row is a lot of work, but worth it IMO.
|
|
|
|
** do not add the vertical margin of main text to first/last row
|
|
|
|
Would make code cleaner. Probably no so difficult.
|
|
|
|
** When a paragraph ends with a newline, compute correctly the height of the extra row.
|
|
** 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.
|
|
|
|
The difficulty for a tall table cell for example, is that it may be
|
|
necessary to break the whole contents to know the width of the cell.
|
|
|
|
|
|
* Description of current drawing mechanism
|
|
|
|
** Three-stage drawing
|
|
|
|
There are three 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 nodraw drawing phase paints the screen (see below) with a null
|
|
painter. The only useful effect is to store the inset positions. + an update() signal is sent. This in turn will trigger a paint
|
|
event, and the actual screen painting will happen then.
|
|
|
|
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.
|
|
+ Update::SinglePar has been specified and the current paragraph has
|
|
not changed height.
|
|
|
|
If a computation of metrics has taken place, Force is removed from the
|
|
flags and ForceDraw is added instead.
|
|
|
|
It is OK to call processUpateFlags several times before an update. In
|
|
this case, the effects are cumulative. processUpdateFlags executes the
|
|
metrics-related actions, but defers the actual drawing to the next
|
|
paint event.
|
|
|
|
The screen is drawn (with appropriate update strategy), except when
|
|
update flag is Update::None.
|
|
|
|
|
|
** Metrics computation (and nodraw drawing phase)
|
|
|
|
This is triggered by bv::updateMetrics, which calls tm::redoParagraph for
|
|
all visible paragraphs. Some Paragraphs above or below the screen (needed
|
|
for page up/down) and computed as needed.
|
|
|
|
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.
|
|
|
|
At the end of the function, bv::updatePosCache is called. It triggers
|
|
a repaint of the document with a NullPainter (a painter that does
|
|
nothing). This has the effect of caching all insets positions.
|
|
|
|
** Drawing the work area.
|
|
|
|
This is done in bv::draw. This method is triggered by a paint event,
|
|
mainly called through 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.
|
|
|
|
BufferView::draw can also be called with a null painter from
|
|
BufferView::updateMetrics().
|