Autocomplete with ALT

When editing maps we often would like to create a new area that fits exactly into an existing area. Manifold provides an autocomplete capability within the Insert Area and Insert Line tool to make this easy. When Snap to mode and an Insert Area or Insert Line command is operational, pressing the ALT key will cause Manifold to autocomplete the area or line between the last clicked coordinate and the current snapped cursor position.

To create an area using autocomplete to follow an existing area:

1. $images\btns_snapto_areas_on.gif$ Engage Snap to Areas.

2. $images\btn_shp_area.gif$ Choose the Insert Area command.

3. Click on the location where the area is to begin.

4. Holding the ALT key down, click on the location where the area is to end.

5. Right-click to create the area.

Autocompletion using the ALT key requires a small amount of manual dexterity that comes with practise. Practise creating areas in this way until the motion is automatic.

Example

$images\sc_autocomplete_01.gif$

We would like to create a new area in the bay shown above. The new area must match exactly the area surrounding it with no overlaps and no gaps.

$images\btns_snapto_areas_on.gif$ We begin by engaging Snap to Areas. The cursor will now move only between the nearest coordinates that define an area.

$images\btn_shp_area.gif$ Choose the Insert Area command. To create an area with this command we left-click onto the coordinates we want to define the area and then we right-click to create the area.

$images\sc_autocomplete_02.gif$

We move the cursor near to the starting coordinate of the new area. The Snap mode jumps the cursor directly to the nearest coordinate of the existing area. We click to mark that coordinate as the starting coordinate for our area.

$images\sc_autocomplete_03a.gif$

If desired, we could move the mouse over all of the coordinates in the existing area and click on each. The Snap mode will assure that any coordinates we click will be coordinates in the existing area. However, it is very tedious to click on all of the coordinates that define the edge of a complex area without missing a few. Missing any coordinates will result in overlaps or gaps.

$images\sc_autocomplete_03.gif$

If Snap to Areas is on, pressing the ALT key during the Insert Area command instructs Manifold to autocomplete the area between the last-clicked point and the current Snap to cursor position. All of the coordinates in between will be chosen for the new area. Autocompletion is indicated by a contrasting tracking/marquee line following the edge of the existing area.

$images\sc_autocomplete_04.gif$

As long as we hold the ALT key down, the autocompleted edge will be shown in black between the initial point and the current mouse position.

$images\sc_autocomplete_05.gif$ $images\sc_autocomplete_05a.gif$

At any time we can lift or hold down the ALT key. Lifting it drops the Insert Area command back into its default mode, where a straight line edge would be created between the previously clicked coordinate and the current mouse coordinate. Pressing the ALT key turns autocompletion back on.

$images\sc_autocomplete_06.gif$

To create the area, while holding the ALT key down we move the mouse cursor to the desired ending position of the area and then we click (while still holding the ALT key down). We can now release the ALT key and right-click to create the area.

$images\sc_autocomplete_07.gif$

The result is an area that is created between the initially clicked point, through all of the coordinates in the edge of the other area and the final clicked point. The new area is shown in blue above.

Shortest Edge and Longest Edge

The ALT key generates an autocompletion boundary following the shortest path from the initially clicked point to the current mouse position. Pressing the SHIFT-ALT key combination generates an autocompletion path following the longest path.

ALT	Autocomplete boundary using the shortest edge path.
SHIFT-ALT	Autocomplete boundary using the longest edge path. Same as ALT when following lines with autocomplete.

$images\sc_autocomplete_08.gif$ $images\sc_autocomplete_10.gif$

Using ALT autocompletes the area boundary using the shortest edge. Using SHIFT-ALT autocompletes using the longest edge.

$images\sc_autocomplete_09.gif$ $images\sc_autocomplete_11.gif$

With ALT the resulting area is a small bay. With SHIFT-ALT the resulting area is a large object that encompasses (is a union of) the original object plus the bay.

Autocompletion across multiple objects

The autocompleted boundary must be all in the same object. One cannot click to start a new area in one object and then try to autocomplete it in a different object. To create areas using more than one other area as the defining boundary, we must use autocompletion in two steps.

$images\sc_autocomplete_12.gif$

To create an area using the two existing areas in the illustration above we begin by clicking on the starting coordinate in the first area (Snap to Areas is enabled and the Insert Areas command is in action).

$images\sc_autocomplete_13.gif$

Holding down the ALT key we move the mouse over the last coordinate in the first area and we ALT-click to mark that coordinate.

$images\sc_autocomplete_14.gif$

Next, we move the mouse cursor slightly downward onto the first coordinate that we would like to use from the second area and we click to mark that location. Note that we simply click on this location and we do not ALT-click.

$images\sc_autocomplete_15.gif$

We can now press ALT and the autocompletion will follow the boundary of the second area from the position of the last click, which is indicated with a red arrow in the illustration above. (Manifold does not draw red arrows as seen above. The red arrow was added to the screen shot.) We can then ALT-click to mark the final coordinate followed by a right-click to create the area.

When using autocompletion across multiple areas it is tempting to work at a high zoom level and to use autoscroll to follow the edge of the areas. When areas are complex, working at a high enough zoom level to be sure to mark the "last" and "next" coordinates of adjacent areas at boundaries between two areas results in a lot of slow autoscrolling.

There are more efficient ways of managing zoom. One alternative is to use the + and - keyboard keys to zoom in and out even in the middle of the Insert Areas command. Pressing + on the keyboard will cause a zoom in. Using the + and - keys we can zoom in where greater precision is required and then zoom out where less precision is required. Using the + and - keys while simultaneously operating the mouse within an Insert Areas command takes some manual dexterity and practise.

A second approach is to work at a zoom level that is convenient for the overall scene and to make a best effort to mark the last and next coordinates at the boundaries between areas. We can then zoom far into the scene at each boundary between areas and add/delete coordinates to the newly created area and move them as desired (using Snap to Areas) to adjust the fine detail of the new area in that location so there are no overlaps or gaps. See the Editing Objects and Editing with Snap topics.

Autocompletion with Lines

We can create lines using autocompletion as well as areas. We can also use lines to guide the autocompletion as well as areas.

$images\sc_autocomplete_16.gif$

For example, suppose we have a line that defines a boundary. We would like to create an area using this line as a guide.

$images\btn_snapto_lines.gif$ We turn on Snap to Lines and $images\btn_shp_area.gif$ Insert Areas. We click on the starting point of the area.

$images\sc_autocomplete_17.gif$

Holding the ALT key down to autocomplete along the line we ALT-click on the ending point of the area.

$images\sc_autocomplete_18.gif$

We can then right-click to create the area.

We can also create lines using areas as a guide.

$images\btns_snapto_areas_on.gif$ To do so we turn on Snap to Areas.

$images\btn_shp_line.gif$ We will create the line with Insert Line.

$images\sc_autocomplete_19.gif$

Suppose we want to create a line at the boundary of two areas. We click on the beginning coordinate.

$images\sc_autocomplete_20.gif$

Next, we ALT-click at the ending coordinate. The ALT key will cause an autocompletion along the edge of the area we are following.

$images\sc_autocomplete_21.gif$

Right-click to create the line. It is shown in the illustration above with a line size of 2 to show the new line better. Note that when creating a line on the common edge of two adjacent areas it doesn't really matter which area is the "upper" area, since both have the same coordinates in common at their adjacent edge.

Keyboard Zoom Commands during Selection and Editing

When making selections or editing objects (such as inserting areas using the Autocomplete feature) we will often want to zoom in or out in the middle of a selection or editing command. Use the + and - keys on the keyboard to do so. Usually the + and - keys in the numeric keypad are used.

+	"Plus" key: Zoom in at the current tool position.
-	"Minus" key: Zoom out at the current tool position.

The current tool position is the position of the mouse at the time the + or - key is pressed. When editing, using these keys allows us to easily zoom into a desired location, make a few precise clicks and then zoom back out and proceed at the usual scale.

Limitations

Autocompletion has several limitations:

· The autocompleted boundary must be all in the same object. One cannot click to start a new are in one object and then try to autocomplete it in a different object. See the notes above when autocompleting across multiple objects.

· Autocompletion works only within the same branch of a multi-branched object.

· When a starting coordinate occurs at a spot where several objects in the same drawing have a defining coordinate, the autocompletion path follows only the topmost object. If desired, we can move an object to a new drawing to force it to be the "topmost".

Notes

The "A" in ALT is a mnemonic for Autocomplete.

The colors used for both the primary marquee (the selection "box") and the autocompletion trackline are set in Tools - Options by the Marquee color. The autocompletion trackline is the RGB color inverse of the Marquee color. When setting Marquee color it is important to choose colors that result in reasonable contrast when the primary marquee and the trackline are seen against the colors used in the drawing.

See the Snap to topic for information on Snap modes.