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livetrax/libs/canvas/container.cc
Robin Gareus 70b00f5201
Canvas: allow to group rendering of child items
> This group functionality can be convenient for performing
> intermediate compositing. One common use of a group is to
> render objects as opaque within the group, (so that they
> occlude each other), and then blend the result with
> translucence onto the destination.
https://www.cairographics.org/manual/cairo-cairo-t.html#cairo-push-group

The main use case where will be to render opaque layered
[MIDI] regions transparently onto a grid.
2022-12-10 02:37:04 +01:00

85 lines
2.0 KiB
C++

/*
* Copyright (C) 2012 Carl Hetherington <carl@carlh.net>
* Copyright (C) 2014-2017 Paul Davis <paul@linuxaudiosystems.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "canvas/container.h"
using namespace ArdourCanvas;
Container::Container (Canvas* canvas)
: Item (canvas)
, _render_with_alpha (-1)
{
}
Container::Container (Item* parent)
: Item (parent)
, _render_with_alpha (-1)
{
}
Container::Container (Item* parent, Duple const & p)
: Item (parent, p)
, _render_with_alpha (-1)
{
}
void
Container::prepare_for_render (Rect const & area) const
{
Item::prepare_for_render_children (area);
}
void
Container::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
{
if (_render_with_alpha == 0) {
return;
} else if (_render_with_alpha > 0) {
context->push_group ();
}
Item::render_children (area, context);
if (_render_with_alpha >= 1.0) {
context->pop_group ();
} else if (_render_with_alpha > 0) {
context->pop_group_to_source ();
context->paint_with_alpha (_render_with_alpha);
}
}
void
Container::compute_bounding_box () const
{
_bounding_box = Rect ();
/* nothing to do here; Item::bounding_box() will add all children for us */
set_bbox_clean ();
}
void
Container::set_render_with_alpha (double alpha)
{
if (_render_with_alpha == alpha) {
return;
}
_render_with_alpha = alpha;
redraw ();
}