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livetrax/gtk2_ardour/editor_canvas.cc

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/*
Copyright (C) 2005 Paul Davis
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., 675 Mass Ave, Cambridge, MA 02139, USA.
$Id$
*/
#include <libgnomecanvasmm/init.h>
#include <jack/types.h>
#include <gtkmm2ext/utils.h>
#include <ardour/audioregion.h>
#include "ardour_ui.h"
#include "editor.h"
#include "waveview.h"
#include "simplerect.h"
#include "simpleline.h"
#include "imageframe.h"
#include "waveview_p.h"
#include "simplerect_p.h"
#include "simpleline_p.h"
#include "imageframe_p.h"
#include "canvas_impl.h"
#include "editing.h"
#include "rgb_macros.h"
#include "utils.h"
#include "time_axis_view.h"
#include "audio_time_axis.h"
#include "i18n.h"
using namespace std;
using namespace sigc;
using namespace ARDOUR;
using namespace PBD;
using namespace Gtk;
using namespace Glib;
using namespace Gtkmm2ext;
using namespace Editing;
/* XXX this is a hack. it ought to be the maximum value of an nframes_t */
const double max_canvas_coordinate = (double) JACK_MAX_FRAMES;
extern "C"
{
GType gnome_canvas_simpleline_get_type(void);
GType gnome_canvas_simplerect_get_type(void);
GType gnome_canvas_waveview_get_type(void);
GType gnome_canvas_imageframe_get_type(void);
}
static void ardour_canvas_type_init()
{
// Map gtypes to gtkmm wrapper-creation functions:
Glib::wrap_register(gnome_canvas_simpleline_get_type(), &Gnome::Canvas::SimpleLine_Class::wrap_new);
Glib::wrap_register(gnome_canvas_simplerect_get_type(), &Gnome::Canvas::SimpleRect_Class::wrap_new);
Glib::wrap_register(gnome_canvas_waveview_get_type(), &Gnome::Canvas::WaveView_Class::wrap_new);
Glib::wrap_register(gnome_canvas_imageframe_get_type(), &Gnome::Canvas::ImageFrame_Class::wrap_new);
// Register the gtkmm gtypes:
(void) Gnome::Canvas::WaveView::get_type();
(void) Gnome::Canvas::SimpleLine::get_type();
(void) Gnome::Canvas::SimpleRect::get_type();
(void) Gnome::Canvas::ImageFrame::get_type();
}
void
Editor::initialize_canvas ()
{
ArdourCanvas::init ();
ardour_canvas_type_init ();
/* don't try to center the canvas */
track_canvas.set_center_scroll_region (false);
track_canvas.set_dither (Gdk::RGB_DITHER_NONE);
track_canvas.signal_event().connect (bind (mem_fun (*this, &Editor::track_canvas_event), (ArdourCanvas::Item*) 0));
track_canvas.set_name ("EditorMainCanvas");
track_canvas.add_events (Gdk::POINTER_MOTION_HINT_MASK|Gdk::SCROLL_MASK);
track_canvas.signal_leave_notify_event().connect (mem_fun(*this, &Editor::left_track_canvas));
track_canvas.set_flags (CAN_FOCUS);
/* set up drag-n-drop */
vector<TargetEntry> target_table;
// Drag-N-Drop from the region list can generate this target
target_table.push_back (TargetEntry ("regions"));
target_table.push_back (TargetEntry ("text/plain"));
target_table.push_back (TargetEntry ("text/uri-list"));
target_table.push_back (TargetEntry ("application/x-rootwin-drop"));
track_canvas.drag_dest_set (target_table);
track_canvas.signal_drag_data_received().connect (mem_fun(*this, &Editor::track_canvas_drag_data_received));
/* stuff for the verbose canvas cursor */
Pango::FontDescription font = get_font_for_style (N_("VerboseCanvasCursor"));
verbose_canvas_cursor = new ArdourCanvas::Text (*track_canvas.root());
verbose_canvas_cursor->property_font_desc() = font;
verbose_canvas_cursor->property_anchor() = ANCHOR_NW;
verbose_canvas_cursor->property_fill_color_rgba() = color_map[cVerboseCanvasCursor];
verbose_cursor_visible = false;
/* a group to hold time (measure) lines */
time_line_group = new ArdourCanvas::Group (*track_canvas.root(), 0.0, 0.0);
cursor_group = new ArdourCanvas::Group (*track_canvas.root(), 0.0, 0.0);
time_canvas.set_name ("EditorTimeCanvas");
time_canvas.add_events (Gdk::POINTER_MOTION_HINT_MASK);
time_canvas.set_flags (CAN_FOCUS);
time_canvas.set_center_scroll_region (false);
time_canvas.set_dither (Gdk::RGB_DITHER_NONE);
meter_group = new ArdourCanvas::Group (*time_canvas.root(), 0.0, 0.0);
tempo_group = new ArdourCanvas::Group (*time_canvas.root(), 0.0, timebar_height);
marker_group = new ArdourCanvas::Group (*time_canvas.root(), 0.0, timebar_height * 2.0);
range_marker_group = new ArdourCanvas::Group (*time_canvas.root(), 0.0, timebar_height * 3.0);
transport_marker_group = new ArdourCanvas::Group (*time_canvas.root(), 0.0, timebar_height * 4.0);
tempo_bar = new ArdourCanvas::SimpleRect (*tempo_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
tempo_bar->property_fill_color_rgba() = color_map[cTempoBar];
tempo_bar->property_outline_pixels() = 0;
meter_bar = new ArdourCanvas::SimpleRect (*meter_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
meter_bar->property_fill_color_rgba() = color_map[cMeterBar];
meter_bar->property_outline_pixels() = 0;
marker_bar = new ArdourCanvas::SimpleRect (*marker_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
marker_bar->property_fill_color_rgba() = color_map[cMarkerBar];
marker_bar->property_outline_pixels() = 0;
range_marker_bar = new ArdourCanvas::SimpleRect (*range_marker_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
range_marker_bar->property_fill_color_rgba() = color_map[cRangeMarkerBar];
range_marker_bar->property_outline_pixels() = 0;
transport_marker_bar = new ArdourCanvas::SimpleRect (*transport_marker_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
transport_marker_bar->property_fill_color_rgba() = color_map[cTransportMarkerBar];
transport_marker_bar->property_outline_pixels() = 0;
range_bar_drag_rect = new ArdourCanvas::SimpleRect (*range_marker_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
range_bar_drag_rect->property_fill_color_rgba() = color_map[cRangeDragBarRectFill];
range_bar_drag_rect->property_outline_color_rgba() = color_map[cRangeDragBarRect];
range_bar_drag_rect->property_outline_pixels() = 0;
range_bar_drag_rect->hide ();
transport_bar_drag_rect = new ArdourCanvas::SimpleRect (*transport_marker_group, 0.0, 0.0, max_canvas_coordinate, timebar_height);
transport_bar_drag_rect ->property_fill_color_rgba() = color_map[cTransportDragRectFill];
transport_bar_drag_rect->property_outline_color_rgba() = color_map[cTransportDragRect];
transport_bar_drag_rect->property_outline_pixels() = 0;
transport_bar_drag_rect->hide ();
marker_drag_line_points.push_back(Gnome::Art::Point(0.0, 0.0));
marker_drag_line_points.push_back(Gnome::Art::Point(0.0, 0.0));
marker_drag_line = new ArdourCanvas::Line (*track_canvas.root());
marker_drag_line->property_width_pixels() = 1;
marker_drag_line->property_fill_color_rgba() = color_map[cMarkerDragLine];
marker_drag_line->property_points() = marker_drag_line_points;
marker_drag_line->hide();
range_marker_drag_rect = new ArdourCanvas::SimpleRect (*track_canvas.root(), 0.0, 0.0, 0.0, 0.0);
range_marker_drag_rect->property_fill_color_rgba() = color_map[cRangeDragRectFill];
range_marker_drag_rect->property_outline_color_rgba() = color_map[cRangeDragRect];
range_marker_drag_rect->hide ();
transport_loop_range_rect = new ArdourCanvas::SimpleRect (*time_line_group, 0.0, 0.0, 0.0, 0.0);
transport_loop_range_rect->property_fill_color_rgba() = color_map[cTransportLoopRectFill];
transport_loop_range_rect->property_outline_color_rgba() = color_map[cTransportLoopRect];
transport_loop_range_rect->property_outline_pixels() = 1;
transport_loop_range_rect->hide();
transport_punch_range_rect = new ArdourCanvas::SimpleRect (*time_line_group, 0.0, 0.0, 0.0, 0.0);
transport_punch_range_rect->property_fill_color_rgba() = color_map[cTransportPunchRectFill];
transport_punch_range_rect->property_outline_color_rgba() = color_map[cTransportPunchRect];
transport_punch_range_rect->property_outline_pixels() = 0;
transport_punch_range_rect->hide();
transport_loop_range_rect->lower_to_bottom (); // loop on the bottom
transport_punchin_line = new ArdourCanvas::SimpleLine (*time_line_group);
transport_punchin_line->property_x1() = 0.0;
transport_punchin_line->property_y1() = 0.0;
transport_punchin_line->property_x2() = 0.0;
transport_punchin_line->property_y2() = 0.0;
transport_punchin_line->property_color_rgba() = color_map[cPunchInLine];
transport_punchin_line->hide ();
transport_punchout_line = new ArdourCanvas::SimpleLine (*time_line_group);
transport_punchout_line->property_x1() = 0.0;
transport_punchout_line->property_y1() = 0.0;
transport_punchout_line->property_x2() = 0.0;
transport_punchout_line->property_y2() = 0.0;
transport_punchout_line->property_color_rgba() = color_map[cPunchOutLine];
transport_punchout_line->hide();
// used to show zoom mode active zooming
zoom_rect = new ArdourCanvas::SimpleRect (*track_canvas.root(), 0.0, 0.0, 0.0, 0.0);
zoom_rect->property_fill_color_rgba() = color_map[cZoomRectFill];
zoom_rect->property_outline_color_rgba() = color_map[cZoomRect];
zoom_rect->property_outline_pixels() = 1;
zoom_rect->hide();
zoom_rect->signal_event().connect (bind (mem_fun (*this, &Editor::canvas_zoom_rect_event), (ArdourCanvas::Item*) 0));
// used as rubberband rect
rubberband_rect = new ArdourCanvas::SimpleRect (*track_canvas.root(), 0.0, 0.0, 0.0, 0.0);
rubberband_rect->property_outline_color_rgba() = color_map[cRubberBandRect];
rubberband_rect->property_fill_color_rgba() = (guint32) color_map[cRubberBandRectFill];
rubberband_rect->property_outline_pixels() = 1;
rubberband_rect->hide();
tempo_bar->signal_event().connect (bind (mem_fun (*this, &Editor::canvas_tempo_bar_event), tempo_bar));
meter_bar->signal_event().connect (bind (mem_fun (*this, &Editor::canvas_meter_bar_event), meter_bar));
marker_bar->signal_event().connect (bind (mem_fun (*this, &Editor::canvas_marker_bar_event), marker_bar));
range_marker_bar->signal_event().connect (bind (mem_fun (*this, &Editor::canvas_range_marker_bar_event), range_marker_bar));
transport_marker_bar->signal_event().connect (bind (mem_fun (*this, &Editor::canvas_transport_marker_bar_event), transport_marker_bar));
/* separator lines */
tempo_line = new ArdourCanvas::SimpleLine (*tempo_group, 0, timebar_height, max_canvas_coordinate, timebar_height);
tempo_line->property_color_rgba() = RGBA_TO_UINT (0,0,0,255);
meter_line = new ArdourCanvas::SimpleLine (*meter_group, 0, timebar_height, max_canvas_coordinate, timebar_height);
meter_line->property_color_rgba() = RGBA_TO_UINT (0,0,0,255);
marker_line = new ArdourCanvas::SimpleLine (*marker_group, 0, timebar_height, max_canvas_coordinate, timebar_height);
marker_line->property_color_rgba() = RGBA_TO_UINT (0,0,0,255);
range_marker_line = new ArdourCanvas::SimpleLine (*range_marker_group, 0, timebar_height, max_canvas_coordinate, timebar_height);
range_marker_line->property_color_rgba() = RGBA_TO_UINT (0,0,0,255);
transport_marker_line = new ArdourCanvas::SimpleLine (*transport_marker_group, 0, timebar_height, max_canvas_coordinate, timebar_height);
transport_marker_line->property_color_rgba() = RGBA_TO_UINT (0,0,0,255);
ZoomChanged.connect (bind (mem_fun(*this, &Editor::update_loop_range_view), false));
ZoomChanged.connect (bind (mem_fun(*this, &Editor::update_punch_range_view), false));
double time_height = timebar_height * 5;
double time_width = FLT_MAX/frames_per_unit;
time_canvas.set_scroll_region(0.0, 0.0, time_width, time_height);
edit_cursor = new Cursor (*this, "blue", &Editor::canvas_edit_cursor_event);
playhead_cursor = new Cursor (*this, "red", &Editor::canvas_playhead_cursor_event);
initial_ruler_update_required = true;
track_canvas.signal_size_allocate().connect (mem_fun(*this, &Editor::track_canvas_allocate));
}
void
Editor::track_canvas_allocate (Gtk::Allocation alloc)
{
canvas_allocation = alloc;
if (!initial_ruler_update_required) {
if (!canvas_idle_queued) {
/* call this first so that we do stuff before any pending redraw */
Glib::signal_idle().connect (mem_fun (*this, &Editor::track_canvas_size_allocated), false);
canvas_idle_queued = true;
}
return;
}
initial_ruler_update_required = false;
track_canvas_size_allocated ();
}
bool
Editor::track_canvas_size_allocated ()
{
if (canvas_idle_queued) {
canvas_idle_queued = false;
}
canvas_width = canvas_allocation.get_width();
canvas_height = canvas_allocation.get_height();
full_canvas_height = canvas_height;
if (session) {
TrackViewList::iterator i;
double height = 0;
for (i = track_views.begin(); i != track_views.end(); ++i) {
if ((*i)->control_parent) {
height += (*i)->effective_height;
height += track_spacing;
}
}
if (height) {
height -= track_spacing;
}
full_canvas_height = height;
}
zoom_range_clock.set ((nframes_t) floor ((canvas_width * frames_per_unit)));
edit_cursor->set_position (edit_cursor->current_frame);
playhead_cursor->set_position (playhead_cursor->current_frame);
reset_hscrollbar_stepping ();
reset_scrolling_region ();
if (edit_cursor) edit_cursor->set_length (canvas_height);
if (playhead_cursor) playhead_cursor->set_length (canvas_height);
if (marker_drag_line) {
marker_drag_line_points.back().set_y(canvas_height);
marker_drag_line->property_points() = marker_drag_line_points;
}
if (range_marker_drag_rect) {
range_marker_drag_rect->property_y1() = 0.0;
range_marker_drag_rect->property_y2() = canvas_height;
}
if (transport_loop_range_rect) {
transport_loop_range_rect->property_y1() = 0.0;
transport_loop_range_rect->property_y2() = canvas_height;
}
if (transport_punch_range_rect) {
transport_punch_range_rect->property_y1() = 0.0;
transport_punch_range_rect->property_y2() = canvas_height;
}
if (transport_punchin_line) {
transport_punchin_line->property_y1() = 0.0;
transport_punchin_line->property_y2() = canvas_height;
}
if (transport_punchout_line) {
transport_punchout_line->property_y1() = 0.0;
transport_punchout_line->property_y2() = canvas_height;
}
update_fixed_rulers();
tempo_map_changed (Change (0), true);
Resized (); /* EMIT_SIGNAL */
return false;
}
void
Editor::reset_scrolling_region (Gtk::Allocation* alloc)
{
TreeModel::Children rows = route_display_model->children();
TreeModel::Children::iterator i;
double pos;
for (pos = 0, i = rows.begin(); i != rows.end(); ++i) {
TimeAxisView *tv = (*i)[route_display_columns.tv];
if (tv != 0 && !tv->hidden()) {
pos += tv->effective_height;
pos += track_spacing;
}
}
double last_canvas_unit = last_canvas_frame / frames_per_unit;
track_canvas.set_scroll_region (0.0, 0.0, max (last_canvas_unit, canvas_width), pos);
// XXX what is the correct height value for the time canvas ? this overstates it
time_canvas.set_scroll_region ( 0.0, 0.0, max (last_canvas_unit, canvas_width), canvas_height);
controls_layout.queue_resize();
}
void
Editor::controls_layout_size_request (Requisition* req)
{
TreeModel::Children rows = route_display_model->children();
TreeModel::Children::iterator i;
double pos;
for (pos = 0, i = rows.begin(); i != rows.end(); ++i) {
TimeAxisView *tv = (*i)[route_display_columns.tv];
if (tv != 0) {
pos += tv->effective_height;
pos += track_spacing;
}
}
RefPtr<Gdk::Screen> screen = get_screen();
if (!screen) {
screen = Gdk::Screen::get_default();
}
/* never let the width of the controls area shrink horizontally */
edit_controls_vbox.check_resize();
req->width = max (edit_controls_vbox.get_width(), controls_layout.get_width());
/* don't get too big. the fudge factors here are just guesses */
req->width = min (req->width, screen->get_width() - 300);
req->height = min ((gint) pos, (screen->get_height() - 400));
/* this one is important: it determines how big the layout thinks it really is, as
opposed to what it displays on the screen
*/
controls_layout.set_size (req->width, (gint) pos);
}
bool
Editor::track_canvas_map_handler (GdkEventAny* ev)
{
track_canvas.get_window()->set_cursor (*current_canvas_cursor);
return false;
}
bool
Editor::time_canvas_map_handler (GdkEventAny* ev)
{
time_canvas.get_window()->set_cursor (*timebar_cursor);
return false;
}
void
Editor::track_canvas_drag_data_received (const RefPtr<Gdk::DragContext>& context,
int x, int y,
const SelectionData& data,
guint info, guint time)
{
if (data.get_target() == "regions") {
drop_regions (context, x, y, data, info, time);
} else {
drop_paths (context, x, y, data, info, time);
}
}
void
Editor::drop_paths (const RefPtr<Gdk::DragContext>& context,
int x, int y,
const SelectionData& data,
guint info, guint time)
{
TimeAxisView* tvp;
AudioTimeAxisView* tv;
double cy;
vector<ustring> paths;
string spath;
GdkEvent ev;
nframes_t frame;
if (convert_drop_to_paths (paths, context, x, y, data, info, time)) {
goto out;
}
/* D-n-D coordinates are window-relative, so convert to "world" coordinates
*/
double wx;
double wy;
track_canvas.window_to_world (x, y, wx, wy);
wx += horizontal_adjustment.get_value();
wy += vertical_adjustment.get_value();
ev.type = GDK_BUTTON_RELEASE;
ev.button.x = wx;
ev.button.y = wy;
frame = event_frame (&ev, 0, &cy);
snap_to (frame);
if ((tvp = trackview_by_y_position (cy)) == 0) {
/* drop onto canvas background: create new tracks */
nframes_t pos = 0;
do_embed (paths, false, ImportAsTrack, 0, pos, false);
} else if ((tv = dynamic_cast<AudioTimeAxisView*>(tvp)) != 0) {
/* check that its an audio track, not a bus */
if (tv->get_diskstream()) {
do_embed (paths, false, ImportToTrack, tv->audio_track(), frame, true);
}
}
out:
context->drag_finish (true, false, time);
}
void
Editor::drop_regions (const RefPtr<Gdk::DragContext>& context,
int x, int y,
const SelectionData& data,
guint info, guint time)
{
const SerializedObjectPointers<boost::shared_ptr<Region> >* sr =
reinterpret_cast<const SerializedObjectPointers<boost::shared_ptr<Region> > *> (data.get_data());
for (uint32_t i = 0; i < sr->cnt; ++i) {
boost::shared_ptr<Region> r = sr->data[i];
boost::shared_ptr<AudioRegion> ar;
if ((ar = boost::dynamic_pointer_cast<AudioRegion>(r)) != 0) {
insert_region_list_drag (ar, x, y);
}
}
context->drag_finish (true, false, time);
}
void
Editor::maybe_autoscroll (GdkEvent* event)
{
nframes_t rightmost_frame = leftmost_frame + current_page_frames();
nframes_t frame = drag_info.current_pointer_frame;
bool startit = false;
static int last_autoscroll_direction = 0;
if (frame > rightmost_frame) {
if (rightmost_frame < max_frames) {
autoscroll_direction = 1;
startit = true;
}
} else if (frame < leftmost_frame) {
if (leftmost_frame > 0) {
autoscroll_direction = -1;
startit = true;
}
} else {
if (drag_info.last_pointer_frame > drag_info.current_pointer_frame) {
autoscroll_direction = -1;
} else {
autoscroll_direction = 1;
}
}
if ((autoscroll_direction != last_autoscroll_direction) || (leftmost_frame < frame < rightmost_frame)) {
stop_canvas_autoscroll ();
}
if (startit && autoscroll_timeout_tag < 0) {
start_canvas_autoscroll (autoscroll_direction);
}
last_autoscroll_direction = autoscroll_direction;
}
gint
Editor::_autoscroll_canvas (void *arg)
{
return ((Editor *) arg)->autoscroll_canvas ();
}
bool
Editor::autoscroll_canvas ()
{
nframes_t new_frame;
nframes_t limit = max_frames - current_page_frames();
GdkEventMotion ev;
nframes_t target_frame;
if (autoscroll_direction < 0) {
if (leftmost_frame < autoscroll_distance) {
new_frame = 0;
} else {
new_frame = leftmost_frame - autoscroll_distance;
}
target_frame = drag_info.current_pointer_frame - autoscroll_distance;
} else {
if (leftmost_frame > limit - autoscroll_distance) {
new_frame = limit;
} else {
new_frame = leftmost_frame + autoscroll_distance;
}
target_frame = drag_info.current_pointer_frame + autoscroll_distance;
}
/* now fake a motion event to get the object that is being dragged to move too */
ev.type = GDK_MOTION_NOTIFY;
ev.state &= Gdk::BUTTON1_MASK;
ev.x = frame_to_unit (target_frame);
ev.y = drag_info.current_pointer_y;
motion_handler (drag_info.item, (GdkEvent*) &ev, drag_info.item_type, true);
if (new_frame == 0 || new_frame == limit) {
/* we are done */
return false;
}
autoscroll_cnt++;
if (autoscroll_cnt == 1) {
/* connect the timeout so that we get called repeatedly */
autoscroll_timeout_tag = g_idle_add ( _autoscroll_canvas, this);
return false;
}
if (new_frame != leftmost_frame) {
reset_x_origin (new_frame);
}
if (autoscroll_cnt == 50) { /* 0.5 seconds */
/* after about a while, speed up a bit by changing the timeout interval */
autoscroll_distance = (nframes_t) floor (current_page_frames()/30.0f);
} else if (autoscroll_cnt == 150) { /* 1.0 seconds */
autoscroll_distance = (nframes_t) floor (current_page_frames()/20.0f);
} else if (autoscroll_cnt == 300) { /* 1.5 seconds */
/* after about another while, speed up by increasing the shift per callback */
autoscroll_distance = (nframes_t) floor (current_page_frames()/10.0f);
}
return true;
}
void
Editor::start_canvas_autoscroll (int dir)
{
if (!session || autoscroll_active) {
return;
}
stop_canvas_autoscroll ();
autoscroll_active = true;
autoscroll_direction = dir;
autoscroll_distance = (nframes_t) floor (current_page_frames()/50.0);
autoscroll_cnt = 0;
/* do it right now, which will start the repeated callbacks */
autoscroll_canvas ();
}
void
Editor::stop_canvas_autoscroll ()
{
if (autoscroll_timeout_tag >= 0) {
g_source_remove (autoscroll_timeout_tag);
autoscroll_timeout_tag = -1;
}
autoscroll_active = false;
}
gint
Editor::left_track_canvas (GdkEventCrossing *ev)
{
set_entered_track (0);
set_entered_regionview (0);
return FALSE;
}
void
Editor::canvas_horizontally_scrolled ()
{
/* this is the core function that controls horizontal scrolling of the canvas. it is called
whenever the horizontal_adjustment emits its "value_changed" signal. it typically executes in an
idle handler, which is important because tempo_map_changed() should issue redraws immediately
and not defer them to an idle handler.
*/
leftmost_frame = (nframes_t) floor (horizontal_adjustment.get_value() * frames_per_unit);
nframes_t rightmost_frame = leftmost_frame + current_page_frames ();
if (rightmost_frame > last_canvas_frame) {
last_canvas_frame = rightmost_frame;
reset_scrolling_region ();
}
update_fixed_rulers ();
tempo_map_changed (Change (0), !_dragging_hscrollbar);
}