[LyX/master] Make the non-drawing cases faster in TextMetrics::drawParagraph

[Jean-Marc Lasgouttes]

commit fc73ebc16c4f0aca76360415a94eca57f283e44e
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Mon Feb 29 16:07:35 2016 +0100

    Make the non-drawing cases faster in TextMetrics::drawParagraph
    
    There are two main cases:
    * when drawing is disabled from the start, use a simplified code that only 
paints insets (in order to cache positions).
    * when the row is not visible, do the same.
    
    The goal of this optimization is to be able to always run a no-drawing draw 
after the metrics have been computed.

diff --git a/src/TextMetrics.cpp b/src/TextMetrics.cpp
index 80ee0aa..69ab7b5 100644
--- a/src/TextMetrics.cpp
+++ b/src/TextMetrics.cpp
@@ -1864,15 +1864,31 @@ void TextMetrics::draw(PainterInfo & pi, int x, int y) 
const
 
 void TextMetrics::drawParagraph(PainterInfo & pi, pit_type const pit, int 
const x, int y) const
 {
-       BufferParams const & bparams = bv_->buffer().params();
        ParagraphMetrics const & pm = par_metrics_[pit];
        if (pm.rows().empty())
                return;
-
-       bool const original_drawing_state = pi.pain.isDrawingEnabled();
-       int const ww = bv_->workHeight();
        size_t const nrows = pm.rows().size();
 
+       // Use fast lane when drawing is disabled.
+       if (!pi.pain.isDrawingEnabled()) {
+               for (size_t i = 0; i != nrows; ++i) {
+
+                       Row const & row = pm.rows()[i];
+                       // Adapt to cursor row scroll offset if applicable.
+                       int row_x = x - bv_->horizScrollOffset(text_, pit, 
row.pos());
+                       if (i)
+                               y += row.ascent();
+
+                       RowPainter rp(pi, *text_, pit, row, row_x, y);
+
+                       rp.paintOnlyInsets();
+                       y += row.descent();
+               }
+               return;
+       }
+
+       BufferParams const & bparams = bv_->buffer().params();
+       int const ww = bv_->workHeight();
        Cursor const & cur = bv_->cursor();
        DocIterator sel_beg = cur.selectionBegin();
        DocIterator sel_end = cur.selectionEnd();
@@ -1909,10 +1925,18 @@ void TextMetrics::drawParagraph(PainterInfo & pi, 
pit_type const pit, int const
 
                RowPainter rp(pi, *text_, pit, row, row_x, y);
 
+               // It is not needed to draw on screen if we are not inside.
                bool const inside = (y + row.descent() >= 0
                        && y - row.ascent() < ww);
-               // It is not needed to draw on screen if we are not inside.
-               pi.pain.setDrawingEnabled(inside && original_drawing_state);
+               pi.pain.setDrawingEnabled(inside);
+               if (!inside) {
+                       // Paint only the insets to set inset cache correctly
+                       // FIXME: remove paintOnlyInsets when we know that 
positions
+                       // have already been set.
+                       rp.paintOnlyInsets();
+                       y += row.descent();
+                       continue;
+               }
 
                if (selection)
                        row.setSelectionAndMargins(sel_beg_par, sel_end_par);
@@ -1929,8 +1953,7 @@ void TextMetrics::drawParagraph(PainterInfo & pi, 
pit_type const pit, int const
                }
 
                // Row signature; has row changed since last paint?
-               if (pi.pain.isDrawingEnabled())
-                       row.setCrc(pm.computeRowSignature(row, bparams));
+               row.setCrc(pm.computeRowSignature(row, bparams));
                bool row_has_changed = row.changed()
                        || bv_->hadHorizScrollOffset(text_, pit, row.pos());
 
@@ -1961,7 +1984,7 @@ void TextMetrics::drawParagraph(PainterInfo & pi, 
pit_type const pit, int const
 
                // Instrumentation for testing row cache (see also
                // 12 lines lower):
-               if (lyxerr.debugging(Debug::PAINTING) && inside
+               if (lyxerr.debugging(Debug::PAINTING)
                        && (row.selection() || pi.full_repaint || 
row_has_changed)) {
                                string const foreword = text_->isMainText() ?
                                        "main text redraw " : "inset text 
redraw: ";
@@ -1999,7 +2022,7 @@ void TextMetrics::drawParagraph(PainterInfo & pi, 
pit_type const pit, int const
                pi.full_repaint = tmp;
        }
        // Re-enable screen drawing for future use of the painter.
-       pi.pain.setDrawingEnabled(original_drawing_state);
+       pi.pain.setDrawingEnabled(true);
 
        //LYXERR(Debug::PAINTING, ".");
 }