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There are five basic cursor shapes: point, polygon, rectangular box, circle,and ellipse. The cursor type is selectable by the corresponding button inthe cursor button submenu (see the button menu section). The latter threecursor types can be used to make "annuli" of concentric equivalent cursors.Only one active cursor can exist at any given time. However, cursors canbe stored, written to disk, and recalled using the "region" features (seethe Region section). The cursor is always displayed, even when it is notactive (not in cursor mode). Since the active point cursor has no visiblecomponent, select it when you do not wish to have a cursor visible in yourdisplay.
When a cursor is selected, its position, size, and orientation aremanipulated by using the mouse (see the mouse control section). As ageneral rule, the left mouse button controls the position of the cursor,the middle mouse button controls the shape or size of the cursor, andthe right mouse button controls the angular orientation of the cursor (ifit has one). You may either "click" or "drag" the mouse. Positions,dimensions, and angles (where applicable) are shared among the latterthree cursors. The point and polygon cursors pose special cases to therule; read about them separately, below.
When SAOimage is in its verbose mode (see the "etc" section), each timea cursor manipulation is completed, a message is sent to SAOimage'sassociated terminal window, giving the cursor coordinates anddimensions, in units of image file pixels.
Positioning
To position the cursor by clicking, move the mouse to the pixel whereyou want to center the cursor and then click the left mouse button.To position the cursor by dragging, press and continue holding downthe left mouse button while moving the mouse. When the cursor ispositioned where you want it to be, release the left mouse button.Note that you can use the magnifier "tracking" feature to aid inpositioning the cursor (see the "etc" section) and you can use thekeyboard arrow keys to aid in fine positioning the mouse (see themouse control or keyboard sections).Sizing
To adjust the size or shape of the cursor, the same clicking or draggingprocedure is used with the middle mouse button to position the cursor'sedge while its center stays fixed. When sizing the box or ellipse,certain restrictions apply, depending on the position of the mouse whenyou first press the middle mouse button. If you are near to a linethrough the center and one corner of the box, you will be controlling thelocation of the corners of the box (adjusting both dimensions). If youare not near one of the diagonals, you will control only the width orheight, depending on the side to which the mouse is closest. The ellipseis adjusted by controlling an imaginary box which encloses the ellipse,having the dimensions of its major and minor axes. When adjusting thesize of a cursor annuli, since the ratio of width to height is fixed,the mouse controls the actual edge of the cursor, regardless of its type.Rotation Angle
The right mouse button is used to control the rotation angle of boxesand ellipses. When the right mouse button is pressed or held down, theangle is determined by a line from the center of the cursor to the mouse.The initial angle (0 degrees) points toward the top of the screen. Toreset the angle to 0 degrees, click on the "ortho" button in the Cursorsubmenu. For the circle cursor, the right button has no function, whilefor points and polygons it performs a special delete function (see below).Point Cursor
The point cursor is used to flag particular image pixels or coordinatepoints. Its position is defined as that of the mouse. No active cursoris drawn. The mouse buttons are mapped directly to region functions (seeregions). The left mouse key stores a point include region (to flag apixel or coordinate of interest). The middle mouse button stores a pointexclude region (to flag a bad pixel). With the mouse positioned to pointat the first character in the label of a saved point, pressing the rightmouse button deletes that saved point.Saved points are represented by a label giving either its pixel coordinatesor an index number. By default, the label is stenciled over the image.However, if the label is too hard to read, the background around the labelcan be made solid by selecting the appropriate command line option. Thepoint is at the left edge of the point label, and on a line with thebottom of the characters (not at the lowest edge of the background). Whenmaking hard copies, SAOimage always fills in the label backgrounds.
Polygon Cursor
A polygon is defined by straight lines connecting a set of vertices. Forthe active polygon cursor, each vertex is represented by a tiny box. Toadd additional vertex points, drag or click with the middle mouse button.The next vertex is always added to the side nearest the mouse pointer whenthe middle button is depressed. To move an existing vertex, point themouse directly at it when depressing the middle mouse button. To delete anunwanted vertex, point the mouse at the unwanted vertex and click the rightmouse button.The entire polygon can be be moved at any time by using the left mousebutton. When the left button is depressed, the polygon is moved such thatthe nearest vertex has the same position as the mouse pointer.
Clicking on any cursor type submenu button, including the "poly", causesthe polygon to be reduced back to a single point. In other words, if youswitch cursor types, you cannot return to the polygon which you had beenconstructing, unless you saved it as a region.
Cursor Annuli
Annuli of box, circle, and ellipse cursors are available by selecting theannuli button from the cursor submenu. Set the cursor to the desired shapeand angle before selecting the annuli feature, as these cannot be changedonce the annuli feature has been selected. (The annuli selection changesthe functioning of the middle mouse button and disables any angle control.)Annuli are sized by clicking or dragging with the middle mouse button.The center, angle, and width to height ratio remain unchanged while sizing.When the middle mouse button is first depressed, three possible events mayoccur, enabling the user to a) create an annulus with an arbitrary radius,b) create annuli with fixed radius increments, or c) change the size of anexisting annulus.
- a) If the mouse is between existing annuli or not too far from an existing annulus, a new annulus will be created sized by the mouse position.
- b) If the mouse is well outside the existing cursor annuli, a new cursor is create which radius is initially incremented from the outer annulus by the same increment as that between the outer two annuli (or the annulus and the center if there is only one annulus). A comparable situation applies when the mouse is well inside the innermost annulus. However, once the annulus is created, if you proceed to drag the mouse with the middle mouse button down, the size of the new annulus reverts to being controlled by the mouse.
- c) If the mouse is pointing at the edge of an existing annulus, that annulus will be "grabbed" for sizing.
- b) If the mouse is well outside the existing cursor annuli, a new cursor is create which radius is initially incremented from the outer annulus by the same increment as that between the outer two annuli (or the annulus and the center if there is only one annulus). A comparable situation applies when the mouse is well inside the innermost annulus. However, once the annulus is created, if you proceed to drag the mouse with the middle mouse button down, the size of the new annulus reverts to being controlled by the mouse.
To delete an unwanted annulus, point the mouse at or near the unwantedannulus and click the right mouse button. The innermost or outermostannulus can be deleted simply by clicking the right mouse button whilethe mouse is inside of outside all of the annuli.
All of the annuli are forgotten when any cursor submenu button isselected, or reselected. The "annuli" button itself toggles between onand off.
Cursor Coloring
Tracking a cursor means updating the displayed cursor as its shape, size,or location is being manipulated, enabling the user to see the effect ofthe manipulation. Tracking a visible cursor across the display poses aspecial problem; how to quickly draw and undraw the cursor as it moveswithout wiping out the image underneath. SAOimage uses two alternativemechanisms to do this.On halftone workstations, the tracking cursor is drawn simply as theopposite color (exclusive or) of the image. Black pixels appear whiteand white pixels appear black, as the the cursor tracks across them.When the tracking action is completed (when the mouse button isreleased), the entire display is redrawn, along with the new cursor.
The same mechanism, as that used on halftone systems, is used on colorworkstations when a large number (>100) of display color levels is needed.During tracking, the inverse of the display pixels may not result in verynoticeable colors, but at least the "shimmering" of the display as thecursor moves makes it possible to see where the cursor is.
When much cursor manipulation is to be performed, a better alternative isavailable. One bit in each color value is reserved for the cursor. Thenthe cursor may be drawn and undrawn without affecting the display. Thisresults in a smooth, continuous display of the cursor throughout anytracking interaction, with no need to redraw the image at the completionof the action. The disadvantage is that the number of available colorsfor the image is cut by a factor of two (plus two more colors for thesaved regions and other overlay-like displays).
On color workstations, one may switch freely between the overlay and non-overlay modes by using the "ovlay" toggle button in the "Color" submenu.See the color section for more details.
