Special items on Curves.-
There are a few points the should be mentioned in relation with the use of the three principal types of curves mentioned in previous paragraphs:
When using first-order continuity curves, placing some defining points very near to others can be negative for maintaining an appealing final aspect. Although the continuity of the tangents is assured, this is not the case with the curvature and big changes of this last in certain points can create a final draw not very soft.
If it is wanted to place two defining points at the same place, this should be done after the curve has been created, editing it. Otherwise, if creating the object it is clicked twice on the same point, it will be create a false object that will disappear from the screen in non-selected state.
It can be placed two or more points in the same place, after the object has been created, editing it and moving some points to the same place. This can be done to create points of discontinuity on the curve or apparently “mixed” curves, as the figure below show using simple beziers.
(The two figures represent the same object, selected and not selected. To make the upper corners, three points have been joined in each corner.)
This “trick” can be used with any one of the three types of curves and it can be useful for creating “solid” objects with “holes”, that can serve as clipping items or for any other kind of figure. Below are shown a couple of examples done using this method.
The blue object is a bezier one and the green object, one nurb (to create the perfect circle inside).
When two or more points in any figure are in the same place, it can be difficult or totally impossible to select one or more of them, as only one of them will be selected. As the defining points of objects are no real objects, the methods explained before will have no utility for solving the problem. Mg5 incorporates an utility for dealing with this situation. It make use of the same button used for changing the order of the stack. Once a point in a curved object is selected, clicking this button (or pressing the key “S”) will select one by one all the other defining points. If the curve is a nurb, after selecting the defining points, it will continue with the points controlling the weights of the points. This operation is cyclic.
The object Nurb, practically, has not been tested in some aspects and the translation from Java to Metapost probably can be improved. In this first version of Mg5 there are some irregularities that will be solved in a short future. The most important detected in the few tests done while writing this Help, is the interchange of the first and last points from the Mg5 screen to the final drawing. If a default arrow is placed, it will be seen on Mg5 screen in the right place (last point) but in the final metapost drawing, it will be placed as a “reverse arrow”, in the first point. If some text over a path is placed on a nurb, it will begin at the last point in direction to the first. This change between those two points should be remembered when using it with arrows and/or curved text.
Madrid, January 2006 |
|