rviz plugin　真难debug

This class is not instantiated by pluginlib::ClassLoader, so the constructor has no restrictions.

DriveWidget( QWidget* parent = 0 );

这个classloader 找半天都找不到

Override sizeHint() to give the layout managers some idea of a good size for this.

virtual QSize sizeHint() const { return QSize( 150, 150 ); }

# why can we just set him a size signal?

Every mouse move event received here sends a velocity because Qt only sends us mouse move events if there was previously a mouse-press event while in the widget.

void DriveWidget::mouseMoveEvent( QMouseEvent* event )
{
  sendVelocitiesFromMouse( event->x(), event->y(), width(), height() );
}

Mouse-press events should send the velocities too, of course.

void DriveWidget::mousePressEvent( QMouseEvent* event )
{
  sendVelocitiesFromMouse( event->x(), event->y(), width(), height() );
}

# both move event and clicked event will triggering an event , event based programming 

When the mouse leaves the widget but the button is still held down, we don’t get the leaveEvent() because the mouse is “grabbed” (by default from Qt). However, when the mouse drags out of the widget and then other buttons are pressed (or possibly other window-manager things happen), we will get a leaveEvent() but not a mouseReleaseEvent(). Without catching this event you can have a robot stuck “on” without the user controlling it.

void DriveWidget::leaveEvent( QEvent* event )
{
  stop();
}

# if you don't explain this explicitly, you better not to explain it. or may fill it with less details. Because even more details make no difference.

Compute and emit linear and angular velocities based on Y and X mouse positions relative to the central square.

void DriveWidget::sendVelocitiesFromMouse( int x, int y, int width, int height )
{
  int size = (( width > height ) ? height : width );
  int hpad = ( width - size ) / 2;
  int vpad = ( height - size ) / 2;

  linear_velocity_ = (1.0 - float( y - vpad ) / float( size / 2 )) * linear_scale_;
  angular_velocity_ = (1.0 - float( x - hpad ) / float( size / 2 )) * angular_scale_;
  Q_EMIT outputVelocity( linear_velocity_, angular_velocity_ );

# that's the core functionality but in order to implement that we need more fixing stuff. code is dirty though.

For the plugin to be found and understood by other ROS packages (in this case, rviz), it needs a “plugin_description.xml” file. This file can be named anything you like, as it is specified in the plugin package’s “manifest.xml” file like so:

<export>
    <rviz plugin="${prefix}/plugin_description.xml"/>
</export>

#　does that rviz at the prefix really matters?

The first line says that the compiled library lives in lib/librviz_plugin_tutorials (the ”.so” ending is appended by pluginlib according to the OS). This path is relative to the top directory of the package:

<library path="lib/librviz_plugin_tutorials">

#where is those lib files?

The next section is a class entry describing the TeleopPanel:

<class name="rviz_plugin_tutorials/Teleop"
       type="rviz_plugin_tutorials::TeleopPanel"
       base_class_type="rviz::Panel">
  <description>
    A panel widget allowing simple diff-drive style robot base control.
  </description>
</class>

This specifies the name, type, base class, and description of the class. The name field must be a combination of the first two strings given to the PLUGINLIB_DECLARE_CLASS() macro in the source file. It must be the “package” name, a “/” slash, then the “display name” for the class.

The type entry must be the fully-qualified class name, including any namespace(s) it is inside.

The base_class_type is either rviz::Panel for a panel class, or rviz::Display for a display class.

The description subsection is a simple text description of the class, which is shown in the class-chooser dialog and in the Displays panel help area. This section can contain HTML, including hyperlinks, but the markup must be escaped to avoid being interpreted as XML markup. For example a link tag might look like: <a href="my-web-page.html">.