In normal viewing mode vector objects are displayed as colored shapes, curves or lines. As explained in Editing vector objects it is possible to do basic editing when still in this mode. However, for more sophisticated editing of an object’s shape it is best to go into Preview mode. The objects then appear in their basic outline without color, that is as vector paths, and the main control points can be seen.
The control points mark the key places along the vector path and are used for altering the shape of the vector object. This is done by manipulating the axis that runs through each control point.
The following section shows you how to modify various types of vector object, for example, a Vector Rectangle and a Bezier Curve.
To modify a vector object two actions must be performed beforehand:
Click on the Modify tool on the Vector tools bar. This displays the Modify Tools Bar, which contains these tools:
Modify Control Points
Sharp Corners
Add Control Point
Remove Control Point
Next, click on the Preview mode tool on the Tools bar. The vector objects are then displayed as vector paths.
Make the control points visible by clicking on the Modify Control Points tool on the Modify Tools Bar and then clicking on the vector object you would like to modify. There will be four control points, one at each corner, for a rectangle; two for an oval, one at the top and one at the bottom; one for each "joint" in a Bezier Curve, that is, at each of the points where you clicked when creating the curve; and so on.
Notes on control points and axes
Each control point (except for those described in 7 below) has an axis running through it in a particular direction (sometimes the axis is not visible i.e. when the control point is at a corner the axis is folded up). The axis is centered on the control point, with the two halves being equal in length.
At either end of the axis there is a handle. Handles are used to turn the axis around the control point, which acts as the center of rotation, and to alter the length of the axis. Changing the direction or length of an axis changes the vector path that runs through the relevant control point. Note that the axis through a control point situated on a curve of the vector path is always at a tangent to the vector path at that control point (if the path at that point is a corner the axis is folded up, and if it is a straight line the axis runs along the line).
As a line is lengthened the vector path around the control point is stretched into a wider curve; as it is shortened the vector path is contracted until it finally becomes a sharp corner when the line is of zero length (as with a square).
Whatever you do with one handle is mirrored by the other handle, that is, the handles act in opposing ways - turning one handle downwards will tilt the opposite handle upwards, dragging one handle outwards will cause the other handle to move an equal distance in the opposite direction, and so on.
The handles can be moved or rotated by dragging with the mouse. Note that you can also drag the control point itself and the line will move as a whole without altering its length or direction.
Alterations in the vector path are restricted to the sections between the adjacent control points on either side of the control point that is being edited.
Some vector objects – especially those that are "open curves", or polygons without a fill color – have start and finish points that "float free". These do not have the normal control point and axis, but either a point without an axis or a one-length axis i.e. there is no mirror axis acting in an opposed way.
Apart from modifying vector objects by dragging control points and handles, you can also add and remove points and turn curves into sharp corners:
Since the vector path is only affected between adjacent control points on either side of the edited control point, you may wish to add or remove control points to restrict or increase the editable range. To add a control point click on the Add Control point tool on the Modify Tools Bar. Next, click on the relevant vector object to active all the current control points. Move the mouse pointer over the point on the vector path where you want the new control point to appear and click once. A control point and axis will be added to the path at this point. The segment of vector path that is affected when editing will thus be reduced. The new control point can be used to alter the vector object, as described in the previous paragraph.
Contrariwise, if you would like to remove a control point, click on Remove Control point on the Modify Tools Bar and then click on the relevant vector object. Next, click once on the control point you would like to remove. The control point will disappear and the segment of vector path that is affected when editing will thus be increased.
Note that after adding or removing a control point you must once again click on the Modify Control point tool and then the vector object to be able to modify the vector path, as described above.
The Sharp Corners tool enables you to convert a control point on a curved vector path into a sharp corner. The axis running through the control point will be reduced to zero length, although you can stretch it out again by dragging in the usual way (the sharp corner will then become a curve again). Convert a control point into a sharp corner by clicking on the Sharp Corners tool and then clicking on the relevant object to activate the control points. Next, click on the control point you would like to convert to a sharp corner.
When you have modified the vector objects to your satisfaction, click on the Preview mode tool on the Tools bar again to switch it off and return to the normal vector object view, with colors restored.