Reduce in half the redraws when scrolling.

Now there's a single fl_scroll() call for each scroll operation,
instead of calling fl_scroll() and then draw().

The patch also fixes support for FL_DAMAGE_EXPOSE in FltkViewport::draw().

Test data:

      FL_DAMAGE_CHILD    = 0x01,    1
      FL_DAMAGE_EXPOSE   = 0x02,    2
      FL_DAMAGE_SCROLL   = 0x04,    4
      FL_DAMAGE_OVERLAY  = 0x08,    8
      FL_DAMAGE_USER1    = 0x10,   16
      FL_DAMAGE_USER2    = 0x20,   32
      FL_DAMAGE_ALL      = 0x80   128

-----------------------------------------------------------------------------.
       | scroll: keys  |      focus click     |      Alt-Tab        | unfocus|
       | or mousewheel | viewport | statusbar | unfocus |    focus  | click  |
-----------------------------------------------------------------------------|
d4235  |     5,5       |   16     |           |   128   |128,128,128|        |
d4529  |     5,5       |   16     |           |   128   |128,128,128|        |
dpatch |     5         |   16     |           |   128   |128,128,128|        |
-----------------------------------------------------------------------------'

</pre>

  The  first  column means dillo version (hg rev). The second one
the  FLTK damage bits received by FltkViewport::draw() per scroll
operation (also viewable at dillo's stdout).

  The  other columns show excessive calls, but that's another bug
that  is not as relevant as scrolling now, so feel free to ignore
them by now.

3 files changed, 20 insertions, 18 deletions

diff --git a/dw/fltkviewbase.cc b/dw/fltkviewbase.cc
index 4778cd87..145d4136 100644
--- a/dw/fltkviewbase.cc
+++ b/dw/fltkviewbase.cc
@@ -434,7 +434,7 @@ void FltkViewBase::finishDrawing (core::Rectangle *area)
 void FltkViewBase::queueDraw (core::Rectangle *area)
 {
    drawRegion.addRectangle (area);
-   damage (FL_DAMAGE_USER1);
+   damage (FL_DAMAGE_USER1);  // USER1 for buffered draw
 }
 
 void FltkViewBase::queueDrawTotal ()
diff --git a/dw/fltkviewport.cc b/dw/fltkviewport.cc
index 707c0bd7..e903e05f 100644
--- a/dw/fltkviewport.cc
+++ b/dw/fltkviewport.cc
@@ -193,34 +193,37 @@ void FltkViewport::draw_area (void *data, int x, int y, int w, int h)
   }
 
   fl_pop_clip();
-
 }
 
+/*
+ * Draw the viewport.
+ *
+ *  + Damage flags come in different ways, draw() should cope with them all.
+ *  + FL_DAMAGE_CHILD can flag scroll bars or embedded FLTK widgets.
+ */
 void FltkViewport::draw ()
 {
    int hdiff = vscrollbar->visible () ? SCROLLBAR_THICKNESS : 0;
    int vdiff = hscrollbar->visible () ? SCROLLBAR_THICKNESS : 0;
    int d = damage();
 
-   if (d & FL_DAMAGE_SCROLL) {
-      clear_damage (FL_DAMAGE_SCROLL);
+   MSG("FltkViewport::draw d=%d  =>  ", d);
+   if (d == (FL_DAMAGE_SCROLL | FL_DAMAGE_CHILD)) {
       fl_scroll(x(), y(), w() - hdiff, h() - vdiff,
                 -scrollDX, -scrollDY, draw_area, this);
-      clear_damage (d & ~FL_DAMAGE_SCROLL);
-   }
-
-   if (d) {
+      MSG("fl_scroll()\n");
+   } else {
       draw_area(this, x(), y(), w () - hdiff, h () - vdiff);
+      MSG("draw_area()\n");
+   }
 
-      if (d == FL_DAMAGE_ALL || hscrollbar->damage ())
-         draw_child (*hscrollbar);
-      if (d == FL_DAMAGE_ALL || vscrollbar->damage ())
-         draw_child (*vscrollbar);
-
-      if (d == FL_DAMAGE_ALL && hdiff && vdiff) {
-         fl_color(FL_BACKGROUND_COLOR);
-         fl_rectf(x()+w()-hdiff, y()+h()-vdiff, hdiff, vdiff);
-      }
+   if ((d & (FL_DAMAGE_ALL | FL_DAMAGE_EXPOSE)) || vscrollbar->damage ())
+      draw_child (*vscrollbar);
+   if ((d & (FL_DAMAGE_ALL | FL_DAMAGE_EXPOSE)) || hscrollbar->damage ())
+      draw_child (*hscrollbar);
+   if ((d & (FL_DAMAGE_ALL | FL_DAMAGE_EXPOSE)) && (hdiff && vdiff)) {
+      fl_color(FL_BACKGROUND_COLOR);
+      fl_rectf(x()+w()-hdiff, y()+h()-vdiff, hdiff, vdiff);
    }
 
    scrollDX = 0;
diff --git a/dw/layout.cc b/dw/layout.cc
index 3535d794..28633c85 100644
--- a/dw/layout.cc
+++ b/dw/layout.cc
@@ -931,7 +931,6 @@ void Layout::resizeIdle ()
 
       // Tell the view about the new world size.
       view->setCanvasSize (canvasWidth, canvasAscent, canvasDescent);
-      //  view->queueDrawTotal (false);
 
       if (usesViewport) {
          int currHThickness = currHScrollbarThickness();