Remove row crc computation

This computation did not make sense anymore since we began to put the
contents in the Row object. The fact that it worked was a coincidence.

Instead, we set rows as changed() on creation and reset that once they
have been drawn. This will allow in the future for a finer definition
of what to redraw or not.

Also update the PAINTING_ANALYSIS document

(cherry picked from commit 9e2da4a3ea)

development/PAINTING_ANALYSIS

@@ -60,6 +60,42 @@ cursor.
 
 * Clean-up of drawing code
 
+** Make SinglePar update flag useful again. 
+
+The current code can be very expensive when moving cursor inside a
+huge table, for example. We should test the flag again, although this
+will probably lead to some glitches here and there.
+
+** 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.
+
+** Create a unique row by paragraph and break it afterwards
+
+This should be a performance gain (only if paragraph breaking still
+shows as expensive after the rest is done)
+
+** 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
 

src/ParagraphMetrics.cpp

@@ -47,8 +47,6 @@
 #include "support/lstrings.h"
 #include "support/textutils.h"
 
-#include <boost/crc.hpp>
-
 #include <algorithm>
 #include <list>
 #include <stack>
@@ -84,42 +82,6 @@ void ParagraphMetrics::reset(Paragraph const & par)
 }
 
 
-size_t ParagraphMetrics::computeRowSignature(Row const & row,
-		BufferView const & bv) const
-{
-	boost::crc_32_type crc;
-	for (pos_type i = row.pos(); i < row.endpos(); ++i) {
-		if (par_->isInset(i)) {
-			Inset const * in = par_->getInset(i);
-			Dimension const d = in->dimension(bv);
-			int const b[] = { d.wid, d.asc, d.des };
-			crc.process_bytes(b, sizeof(b));
-		} else {
-			char_type const b[] = { par_->getChar(i) };
-			crc.process_bytes(b, sizeof(char_type));
-		}
-		if (bv.buffer().params().track_changes) {
-			Change change = par_->lookupChange(i);
-			char_type const b[] = { static_cast<char_type>(change.type) };
-			// 1 byte is enough to encode Change::Type
-			crc.process_bytes(b, 1);
-		}
-	}
-
-	pos_type const b1[] = { row.sel_beg, row.sel_end };
-	crc.process_bytes(b1, sizeof(b1));
-
-	Dimension const & d = row.dimension();
-	int const b2[] = { row.begin_margin_sel,
-	                   row.end_margin_sel,
-	                   d.wid, d.asc, d.des };
-	crc.process_bytes(b2, sizeof(b2));
-	crc.process_bytes(&row.separator, sizeof(row.separator));
-
-	return crc.checksum();
-}
-
-
 void ParagraphMetrics::setPosition(int position)
 {
 	position_ = position;

src/ParagraphMetrics.h

@@ -85,9 +85,6 @@ public:
 	///
 	bool hfillExpansion(Row const & row, pos_type pos) const;
 
-	///
-	size_t computeRowSignature(Row const &, BufferView const & bv) const;
-
 	///
 	int position() const { return position_; }
 	void setPosition(int position);

src/Row.cpp

@@ -162,20 +162,13 @@ Row::Row()
 	: separator(0), label_hfill(0), left_margin(0), right_margin(0),
 	  sel_beg(-1), sel_end(-1),
 	  begin_margin_sel(false), end_margin_sel(false),
-	  changed_(false), crc_(0),
+	  changed_(true),
 	  pit_(0), pos_(0), end_(0),
 	  right_boundary_(false), flushed_(false), rtl_(false),
 	  changebar_(false)
 {}
 
 
-void Row::setCrc(size_type crc) const
-{
-	changed_ = crc != crc_;
-	crc_ = crc;
-}
-
-
 bool Row::isMarginSelected(bool left_margin, DocIterator const & beg,
 		DocIterator const & end) const
 {

src/Row.h

@@ -139,9 +139,7 @@ public:
 	///
 	bool changed() const { return changed_; }
 	///
-	void setChanged(bool c) { changed_ = c; }
-	///
-	void setCrc(size_type crc) const;
+	void changed(bool c) const { changed_ = c; }
 	/// Set the selection begin and end.
 	/**
 	  * This is const because we update the selection status only at draw()
@@ -315,8 +313,6 @@ private:
 
 	/// has the Row appearance changed since last drawing?
 	mutable bool changed_;
-	/// CRC of row contents.
-	mutable size_type crc_;
 	/// Index of the paragraph that contains this row
 	pit_type pit_;
 	/// first pos covered by this row

src/TextMetrics.cpp

@@ -468,7 +468,7 @@ bool TextMetrics::redoParagraph(pit_type const pit)
 		row.pit(pit);
 		need_new_row = breakRow(row, right_margin);
 		setRowHeight(row);
-		row.setChanged(false);
+		row.changed(true);
 		if (row_index || row.endpos() < par.size()
 		    || (row.right_boundary() && par.inInset().lyxCode() != CELL_CODE)) {
 			/* If there is more than one row or the row has been
@@ -1888,8 +1888,7 @@ void TextMetrics::drawParagraph(PainterInfo & pi, pit_type const pit, int const
 				row.end_margin_sel = sel_end.pit() > pit;
 		}
 
-		// Row signature; has row changed since last paint?
-		row.setCrc(pm.computeRowSignature(row, *bv_));
+		// has row changed since last paint?
 		bool row_has_changed = row.changed()
 			|| bv_->hadHorizScrollOffset(text_, pit, row.pos())
 			|| bv_->needRepaint(text_, row);
@@ -1907,6 +1906,7 @@ void TextMetrics::drawParagraph(PainterInfo & pi, pit_type const pit, int const
 			// Paint only the insets if the text itself is
 			// unchanged.
 			rp.paintOnlyInsets();
+			row.changed(false);
 			y += row.descent();
 			continue;
 		}
@@ -1958,6 +1958,8 @@ void TextMetrics::drawParagraph(PainterInfo & pi, pit_type const pit, int const
 
 		// Restore full_repaint status.
 		pi.full_repaint = tmp;
+
+		row.changed(false);
 	}
 
 	//LYXERR(Debug::PAINTING, ".");