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Viewer(3U) InterViews Reference Manual Viewer(3U)


Viewer - displays a graphical component view hierarchy


#include <Unidraw/viewer.h>


A Viewer displays a graphical component view and provides an interface to scrolling and zooming it. The viewer also processes user input events and generates the appropriate calls on Unidraw objects in response. The Viewer class is a derived from GraphicBlock; thus it can draw the structured graphics hierarchy embodied in GraphicView's graphic. A viewer uses a damage object to keep the screen up to date. Viewer's sensor catches up and down events, and its Handle implements implements the tool manipulation loop.



Both constructors take the enclosing editor, the GraphicView object that the viewer will display, a page object, and optionally a grid, a natural width and height, initial page orientation, alignment, and zooming specifications. The second form adds a parameter for specifying the Viewer's instance name.
Viewer augments GraphicBlock's Update semantics by repairing any damage that has been accumulated. In addition, Update will replace its graphical view if its subject differs from the editor's component; in that case, it will create a graphical view of the editor's component, delete its own view, and replace it with the new one.
Viewer's Adjust operation will automatically update the editor's MagnifVar (if it defines one) to reflect the current magnification.
By default, Handle employs the editor's current tool on a LEFTMOUSE down event. On MIDDLEMOUSE or RIGHTMOUSE down events, it momentarily engages the editor's MoveTool or SelectTool, respectively, allowing the user to move or select a graphical component without changing the current tool explicitly. Nothing happens if the editor does not define a keyboard equivalent for engaging these tools. The Handle function calls either the UseTool or MomentaryUseTool protected member functions (described below) in response to these events.
Explicitly set or get a constructor-specified parameter. The Set operations delete the value they replace if it is different from the given one.
Viewer's SetMagnification operation amends GraphicBlock::SetMagnification to set the value of the enclosing editor's MagnifVar, if it defines one.
Set and get the viewer's orientation parameter, which specifies whether the graphical view, page, and grid will appear in portrait or landscape mode. No transformation will be applied in portrait mode, while landscape mode will rotate the page -90 degrees and translate it vertically by an amount equal to the width of the page's bounding box.
Return the enclosing editor's selection object; it is equivalent to calling GetEditor and then calling GetSelection on the result.
Return the viewer's damage object.
These operations let Rubberband and TextDisplay instances appear to work in a viewer by allowing them to draw on the viewer's canvas. InitRubberband sets the rubberband's canvas to the viewer's and initializes its painter as well. InitTextDisplay likewise sets the TextDisplay's canvas to the viewer's. It also modifies the given painter's background color to match the viewer's and supplies the painter to the TextDisplay for its use.
Incur minimal damage on the viewer's damage object to account for the TextDisplay's current size. The TextDisplay's painter must be passed explicitly.
Convenience functions for adjusting the viewer's perspective. CenterOp centers the page in the viewer's canvas without changing the magnification. Magnify scrolls and magnifies the given area (in canvas coordinates) so that it fills the viewer's canvas. Magnify ensures that the area will remain fully visible in the viewer. ReduceToFit scrolls and reduces the view so that the entire page is visible.
Constrain the supplied coordinates to fall on the nearest grid point if the viewer defines a grid and if the enclosing editor defines an active GravityVar.
Commence direct-manipulation with the given tool without an explicit action on the user's part. Normally, direct manipulation with the currently engaged tool (as returned by the editor's GetCurTool operation) starts automatically when the user clicks in the viewer.
Align the graphical component with respect to viewer's canvas, assuming a view of the component appears in the viewer. For example, a ``Center'' alignment will align the component's center with the canvas'; a ``BottomLeft'' alignment will align the component's bottom-left corner to the canvas'.



Initialize the viewer's member variables. The first form of this operation initializes all parameters that can be passed to a constructor. The first form calls the second form, which initializes a subset of the attributes that may change independently of the others.
A convenience function equivalent to calling the same operation on the enclosing editor.
Return the transformer that the viewer uses to implement scrolling and zooming.
This operation implements a direct manipulation loop governed by the given manipulator. First it calls Grasp on the manipulator with the given event. Then it reads events in a loop, calling the manipulator's Manipulating operation with each new event. When Manipulating returns false, it calls Effect on the manipulator with the event read last.
Helper functions for initiating direct manipulation with tools and executing their effect. UseTool first instructs the given tool to create a manipulator, and then it calls Manipulate to carry the manipulation through to completion. Next it asks the tool to interpret the manipulator, which in turn may produce a command. Finally, UseTool executes and logs the command produced. MomentaryUseTool simply engages the given tool, calls UseTool, and re-engages the original tool.
A helper function that rotates the viewer's graphic to reflect its current orientation.
A helper function used in SetMagnification to notify the enclosing viewer's MagnifVar (if it defines one) of the change in magnification.
Returns the view category (see classes(3U)) the viewer will use to instantiate a view if it is not given one explicitly. ViewCategory returns COMPONENT_VIEW by default.


Damage(3U), Editor(3U), Event(3I), Graphic(3U), GraphicBlock(3U), GraphicComp(3U), GraphicView(3U), Grid(3U), Manipulator(3U), MoveTool(3U), Page(3U), Perspective(3I), Rubband(3I), SelectTool(3U), Selection(3U), Sensor(3I), TextDisplay(3I), Tool(3U), classes(3U), globals(3U), statevars(3U)

6 October 1990 Unidraw