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
+sections 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!!!
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,
cursor.
-* Clean-up of drawing code
+* TODO 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.
+a full screen update (at top level, at least). Only the rows after the
+current one need to have their position recomputed.
-This is also true when scrolling (how to do that?)
*** redoParagraph
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
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.
+Also, the anchor is relative to the outer paragraph, which means that
+for a very long inset it is necessary to rebreak until the contents
+that needs to be shown (to compute the heights).
+
+All in all, this is difficult to get right. This is less important now
+that SinglePar updates work in nested insets.
* Description of current drawing mechanism
+ 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.
+ normal and math) in bv::coordCache and the vertical position of the
+ top-level paragraphs.
+ the nodraw drawing phase paints the screen (see below) with a null
- painter. The only useful effect is to store the inset positions.
+ painter. The only useful effect is to store the positions of
+ visible insets.
+ an update() signal is sent. This in turn will trigger a paint
event, and the actual screen painting will happen then.
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:
+DecorationUpdate). It triggers a call to updateMetrics 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.
+ 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
+It is OK to call processUpdateFlags 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.
** 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.
+This is done bv::updateMetrics. When the parameter 'force' of this
+method is true, that first thing that is done is to clear the metrics
+caches to start from a clean slate.
+
+Then, starting upwards then downwards from the anchor paragraph
+(anchor_pit_) and its vertical position (anchor_ypos_),
+tm::updateMetrics every visible paragraph whose metrics is not know
+(all of them when force==true) is recomputed using tm::redoParagraph.
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.
+all the paragraphs of the inset. Then, a single big row is created in
+tm::tokenizeParagraph, which is later broken in multiple rows by
+tm::breakParagraph.
-At the end of the function, bv::updatePosCache is called. It triggers
+If it turns out that the top or bottom margin are incorrect (paragraphs
+are too high/low), tm::updateMetrics will be called again with fixed
+values of anchor_ypos_ (this does not incur much extra work).
+
+At the end of bv::updateMetrics, 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.
+This way of working means that scrolling can be achieved by just
+updating anchor_ypos_ and calling bv::processUpdateFlags(Update::ForceDraw).
+
** Drawing the work area.
This is done in bv::draw. This method is triggered by a paint event,
projects / lyx.git / blobdiff