Control Panel. The set of buttons and menus at the top of the Gargoyle viewer.

Feedback Line. A one line label at the bottom of the control panel in which Gargoyle displays feedback and error messages for the user.

Scene. The set of graphical objects currently in the Gargoyle viewer. The scene includes the graphical objects created by the user and alignment lines created by Gargoyle for the user.

Segment. A single straight line segment, circular arc, piece of a conic, cubic Bezier curve, or interpolating spline. A segment has two endpoints called joints.

Joint. An endpoint of a segment. Every segment has two joints. Joints are drawn in Gargoyle as small squares which are normally invisible, become solid white squares with a dot in the center as needed for attracting the caret or when a related object is selected, and become solid black squares when they are selected.

Control point. Curved segments have additional points associated with them, called control points, which define their shape. Control points are drawn in Gargoyle as small solid squares which are normally invisible, become solid white squares as needed for attracting the caret or when a related object is selected, and become solid black squares when they are selected.

Trajectory. A connected sequence of line segments and/or curve segments. Trajectories may be open or closed; a closed trajectory is called a fence.

Outline. A set of trajectories considered as a group for some purposes. Most outlines contain a single trajectory, but a closed trajectory with holes in it is represented by a single outline composed of several trajectories.

Holes. An outline may consist of a single closed trajectory (a fence), and a number of subsidiary closed outlines called holes. The fence and its holes are rendered using wrap numbers; the graphical effect is that of a window or hole through the opaque fence through which scene objects behind the fence appear. See Holes in the Hierarchy menu below.

Fence. See Holes.

Slice. A graphical object which is not a part of the segment/trajectory/outline hierarchy. Slices currently do not participate in groups of graphical objects. Slices usually have special behavior defined via a classing mechanism supported in the implementation of Gargoyle. Text strings, boxes, circles, and pieces of Interpress files are currently implemented as slices.

Top level object(s). A set of outlines or slices considered as a group for some purposes.

Caret. The upside-down V shaped object which appears during most interactive operations. The caret is used as the first endpoint of new segments, the insertion point for new text strings, the center of new circles, -- in general, the start point of new graphical objects. It also acts as a kind of tugboat, pulling selected objects toward some object to which it is attracted by gravity. The anchor is always created at the caret position.

Anchor. The center of rotation and the center of scaling. Currently appears as four arrows pointing away from a circle. The anchor is gravity-active and hot.

Hot Objects. A joint or segment is hot if it triggers alignment lines. Hot joints can trigger slope lines, and compass circles. Hot segments can trigger angle lines and parallel "distance" lines. The anchor acts as a hot joint. Segments and joints are made hot or cold by explicit user actions and by heuristics based on the operation being performed. Hot joints are drawn in Gargoyle as white squares larger than the squares used to show control points.

Alignment line. A greyed straight line or circle for use during an operation which requires precision, such as dragging, rotating, scaling, and rubberbanding. Which lines appear depends on the objects in the scene which generate the lines (explicitly hot objects and objects chosen by heuristics based on the operation being performed), and which types of alignment objects the user has activated on the control panel. Alignment lines are gravity active.

Gravity. The mapping from cursor position to caret position. This mapping often lands the caret onto a trajectory in the scene or an alignment line; the caret is "snapped" to a gravity active object when the cursor moves to within the gravity extent of that object. Two types of gravity are available, called Prefer Points gravity and Strict Distance gravity. The user interactively chooses the desired type. The user may also turn gravity off completely, even in the middle of another operation (like dragging)..

Gravity Active. An object is gravity active if the caret will "snap" to that object during a caret positioning operation or an operation using caret motion such as dragging, rotating, scaling, and rubberbanding. All objects in a scene which are not themselves in motion will be gravity active, all alignment lines are gravity active, and some intersection points among alignment lines and scene objects are gravity active.

Gravity Extent. The farthest the cursor can be from a gravity sensitive object and still map the caret onto that object. The user interactively sets the gravity extent.

NYI. Not yet implemented.

Select Joint. Hold down the left mouse button and move around. If gravity snaps the cursor onto a joint or control point, the joint or control point will temporarily be highlighted (appear as a filled black square). If a point is highlighted, its related joints and control points will also appear, unhighlighted. Releasing at this point will cause all previously selected objects to be deselected and that joint or control point to become selected. This operation is called selecting at the joint level. N.B.: it is easy to confuse this operation with the CaretPosition operation; see below.

Select Segment. Hold down the middle mouse button and move around. If gravity snaps the cursor onto a segment, its end joints will temporarily be highlighted (appear as a filled black square) and the segment will be highlighted using a black stroke twice the width of the actual segment stroke width.. If the segment is a curve its control points will appear. Releasing at this point will cause all previously selected objects to be deselected and that segment to become selected. The segment, joints, and control points will remain highlighted as selection feedback. This operation is called selecting at the segment level.

Select Trajectory. Double click the middle mouse button, holding down on the second stroke. Then move around as in Select Joint. If gravity snaps the cursor onto a trajectory, all of its joints and segments become hightlighted. Releasing at this point will cause all previously selected objects to be deselected and that trajectory to become selected. This operation is called selecting at the trajectory level.

Select TopLevel. Double click the left mouse button, holding down on the second stroke. Then move around as in Select Joint. If gravity snaps the cursor onto a top level object, all of its trajectories, joints and segments become hightlighted. Releasing at this point will cause all previously selected objects to be deselected and that top level object to become selected. This operation is called selecting at the top level. Outlines and slices are selectable at the top level. Top level selection may be extended to any number of top level objects.

Extend Selection. Hold down the right mouse button and move around. If gravity snaps the cursor onto an object of the same level as the initial selection level, releasing at this point will ADD the object to the current selection. Extend selection operations are often repeated to build a temporary collection of objects for operands to an interactive operation. Note that extending at the segment level within a single trajectory will make a new selection of all segments in that trajectory between the original selected segment and the extended segment. Since trajectories are ordered, extend segment selection may wrap around from the end to the beginning of a trajectory.

META Extend Selection. Hold down the SWAT key and initiate a selection operation (Select Joint/Segment/Trajectory/TopLevel). Continue just as before with selection feedback. When you release the mouse button and the SWAT key, the selected object will be ADDED to the existing selection rather than replacing the existing selection. It is thus possible to (meta)select heterogeneous objects, say a mixture of joints, segments, and trajectories, for a subsequent operation like Drag or Delete.

Select with Box. Double click the right mouse button, holding down on the second stroke. A box will appear which may be rubberbanded exactly as in the Add Box command (below). When the button is released, the box will disappear and all objects whose bounding box lies within the box will become the current selection.

Deselect Joint/Segment/Trajectory/TopLevel. Hold down CTRL and SHIFT to convert selection operations into deselection operations. Use the same mouse buttons as in the corresponding selection operations.

ExtendDeelection. NYI.

Caret Position. ShiftLeftMouse initiates caret positioning. The caret will interactively follow the cursor and use gravity to snap onto gravity active points and lines as long as the mouse is held down and moved. The feedback line will display useful information during this operation. N.B.: it is easy to confuse this operation with the SelectJoint operation; the CaretPosition operation will not change the current selection.

Add Line. Create a new straight line segment whose endpoints are the caret and the current cursor position. ShiftMiddleMouse initiates AddLine. Holding down the mouse button causes new alignment lines of the activated types to appear (if the Heuristics option is on) and the caret to jump to the cursor so the new endpoint can be placed with precision. The user may continue to hold down the mouse button and move the mouse; the new line will be rubberbanded accordingly.

Add Box. Create a new box object whose corners are the caret and the current cursor position. ShiftRightMouse initiates AddBox. Holding down the mouse button and moving the mouse causes alignment lines to appear (if the Heuristics option is on) and the caret to jump to the cursor corner of the box, so the new corner can be placed with precision. The user may continue to hold down the mouse button and move the mouse; the new box will be rubberbanded accordingly. Boxes may be translated/rotated/scaled as usual and will retain their box characteristics. Boxes are displayed with control points at their corners and center. Dragging a corner or an edge of a box will grow/shrink the box rectilinearly. Transforming a box selected as a trajectory or top level object will transform the entire box.

Drag. CtrlLeftMouse initiates dragging. All selected objects are translated, maintaining a constant relationship to the caret. Dragging is usually performed in stages. First, select the objects to be dragged; if parts of trajectories are selected, then those trajectories will be rubberbanded. Second, place the caret on that joint or segment which must be positioned with precision if the selection operation has not already positioned the caret for you. Next, position the cursor as desired. As the mouse button is pushed down, the caret will snap to the cursor. Finally, continue to hold down the CTRL key and the mouse button and move the mouse. The caret will be attracted to gravity-sensitive objects as usual, taking all of the selected objects with it.

Rotate. CtrlMiddleMouse initiates rotation. Very much like Drag. Rotate requires one extra preliminary step -- the anchor must be placed to be used as a center of rotation. This can be done using the DropAnchor command in the HotSpots menu, or from the keyboard (CtrlA drops the anchor at the caret. CtrlShiftA deletes the anchor). Select the objects to be rotated; if parts of trajectories are selected, then those trajectories will be rubberbanded. Because the objects move with 1 degree of freedom while the mouse has two, the caret does not remain in a constant relationship with the objects being rotated. However, the caret does snap to the cursor when the operation begins so objects can be rotated with precision. The angle of rotation is the angle between two vectors: the Anchor to initial-caret-position vector, and the Anchor to current-caret-position vector.

Scale. CtrlRightMouse initiates scaling. Very much like rotate. The Anchor is the center of scaling. The scaling factor is the ratio of <the current caret to Anchor distance> to <the initial caret to Anchor distance>. Scaling to zero is discouraged.

Skew. CtrlDoubleRightMouse initiates an interactive skewing transformation. Skew is similar to Drag. The line of invariance is the line that passes through the anchor and is perpendicular to the line from the anchor to the initial caret position. The scene point at which the caret was placed before the operation is translated to stay with the caret, skewing everything else as necessary. This operation is experimental and will probably be bound to a different mouse button in the near future.

Copy And Drag. CopyAndDrag is initiated by CtrlDoubleLeftClick. Hold down the CTRL key and double click. A copy of the selection is created and then selected. It may be immediately dragged by moving the mouse without releasing the button. The copy will first appear translated from the original by the vector defined by the caret and cursor when Copy And Drag is initiated.

Scroll, Zoom, Fit, and Prev. The BiScrollers package provides horizontal and vertical scrolling for Gargoyle scenes and also provides some temporary view operations via the first button line of the control panel. These operations (Scale, Rotate, Fit, Reset, Edge, Prev) should not be confused with the permanent operations applied to Gargoyle scene objects using Gargoyle operations. BiScrollers transformations and how to use them to help view a scene are described in BiScrollersDoc. These buttons are PopUpButtons; holding the mouse button down over one of them for about one second will cause a pop-up menu to appear. See PopUpButtonsDoc for more information. There are two additional buttons, CenterSel and FitSel, on this line. CenterSel will cause the bounding box of the currently selected Gargoyle objects to be centered in the viewer. If there is no selection, the caret position will be centered in the viewer. FitSel will cause a BiScrollers Fit operation so that the bounding box of the currently selected Gargoyle objects is scaled and translated to fit in the viewer. The Prev button is like the Tioga PrevPlace button; it returns the viewport to where it was at the last BiScrollers operation with the exception of Scroll, Scale, and Rotate. In other words, scrolling, scaling, and rotating do not change the previous place; other BiScroller operations remember their current place before transforming the viewport. Invoking the Prev button causes the previous place and the current place to swap.