In the next lines we will look at the available buttons for creating objects and we will speak about the way of using them. Nevertheless, before, we have to say a couple of words in relation with two buttons that appear at the top part of the principal button-box, at left. From left to right and from top to bottom we find what follows:
1- The "thick vertical arrow" is the button for transforms. If we want to manipulate an image through affine transformations, we have to use it. If it is clicked, the "Select Transform" window will appear. This button is in close relation with the principal Slider, in such a way that before clicking on it and depending on the transformation choosen, it is necessary to move the Slider to the place needed. Once the button is clicked, the Slider is locked.
2- The second button is just a "making-life-easier" button. If clicked, all the objects on the screen are grouped and then selected. As this is something that usually is done many times, with this button the whole operation is done quicker and simpler. Suppose that we want to "rotate" an image. There is no specific rotation-button in MG but we can do as follows:
The next four buttons have been already explained or correspond to 3-D functions, so lets continue with the one after those.
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3- The first one in this series is the "Text" button, easily identifiable through the big "T" on its face. Although "text" will be explained with big detail later on, in another chapter, we will say already a couple of words. To put some text in a draw the process is as follows: First, something must be written in the upper Text Field. Anything according with TeX/LaTeX rules -if some PostScript font is not choosen- anything can be written, including "$math_symbols$". Once finished the "T" button must be clicked and with the mouse pointer a line must be drawn in the screen. The written text will appear over the line, left justified, as soon as the right button is clicked. Nevertheless, in the final MP figure, the text will be "center_justified" and the horizontal and vertical center will be the origin of the line just drawn. As will be seen, the line can have any direction, not necessarily horizontal.
4- The next button is the "oblique_arrow" button, and this is a "real" arrow button. Its function is to place arrow-heads of many different kinds over the end of open lines or curves. Once clicked, the "arrow_panel" will be visible. This is a quite simple window as it is, in some way, self-explaining. So, at left we find six "radio" buttons related with the shape of the arrowhead. In second place, there are also five small buttons to choose the size of the arrowhead, and in third place there are six other buttons to choose the angle of the arrow. On the upper part we can choose between a typical MetaPost arrow -the round one- or a totally acute one (Beware! the length of the total arrow increases slightly, breaking the extremely precise joints usually found in MP. We will find a solution someday.). At right-top there is a "big" button to "unfill" arrows and the other small buttons to choose from a single arrowhead at the last point drawn of a line, or a double arrow at both limits. Downward, it is possible to change the point where the arrowhead has been "placed", and place it over the beginning of the line. As can be seen, quite a lot of possibilities.
Once the kind of arrow choosen, the line where we want it placed must be selected (so, in red). Then it is enough to CLICK A SECOND TIME THE SAME BUTTON (sometimes a third time is also needed) that has launched the arrow-panel and the line will have an arrow in one or both extremes (it will be seen in the canvas, just a small blue point at the point where the arrow is placed). Some interesting points must be mentioned: the placement of arrows will be done on all the objects selected when we click. This is very convenient when we want to put arrows on many lines; we do not need to place one arrow a time. On the contrary, we select all the lines which we want to have an arrow and place it at the same time on all those lines, just clicking once. Another important issue is that if we make a mistake and place the wrong arrow, it is extremly simple to correct it. The only thing to do is to click the radiobuttons needed on the arrow-panel and place once more the arrows on the line/s. The first arrows will be deleted and the new ones will appear in due places. Finally, we can delete any arrow on any line: to do it, we must click the big upper-left button on the arrow-panel, the one with the title "Clear". This is the same as selecting the arrow: "no-arrow". So, placing it will erease any arrow over the line. We must not forget to click once more the "Clear" or the "Unfill" button to let the fonction of the panel in the original state. On METAGRAF's screen, the arrows will appear as a single blue point where we have placed them.
5- This button must be clicked to create a rectangle-object that, if transformed, can be converted to any kind of parallelogram, although modifying its "attributes". When "NOT" transformed, we are in front of the typical rectangle found in so many programs that has its sides parallels to horizontal and vertical axis. Just with the pointer of the mouse it is possible to change its dimensions, size...and so on. It is very simple to use and convenient for many applications. That's the reason why I have maintained it. But, sometimes, this simple rectangle is "too simple". If working in 3-D -but also in 2-D- if we want to rotate our objects or just to look at them from another point of view, the "simple-rectangle" is useless as it has no permission to change its axis-parallel behavior. The solution (versatility once more) is to do an affine transformation. Once transformed, our simple rectangle changes to a sophisticated one. Now it can be rotated through any one of the three Cartesian axis or change its dimensions and/or orientation...anything, BUT....everything must be done through affine transformations, so we will see how our four points in the corners (before, presents), disappear and we can only translate it in the usual way. I repeat, any other modification to its size and/or shape must be done with affine transformations. Quite sophisticated our rectangle object!
6- The oval or ellipse object is just the "sister" of the rectangle and has the same attributes. The same change from Dr.Jekyll to Mr.Hyde if we transform it and the same capabilities to satisfy all our pretensions.
7- The right line is probably (with the sole exception of the point) the simplest object to manipulate. Just by clicking on this button, and then clicking and dragging over the screen a line is created. Once done, to modify it is as simple as has been its creation. To translate it, it is enough to click on any part of the rectangle limited by its extreme points; and to change its orientation and/or length is just a matter of selecting one of the extreme points with the special mouse cursor and move it in any direction. This object accept any kind of transformation without changing its "peculiarities". Moreover, it is the base of the written text, as we have said before, and the positioning of this last is based on the line. The only characteristic that doesn't matter for the text, is the length of the line.
If the button is clicked after pressing the CTRL-key, the object choosen is the poly-line. It behaves like a polygone but is not necessarily closed.
8- We have spoken already about the standard circle of METAGRAF. It is an extremely versatile object that maintains all its initial properties submitted to any kind of direct or affine changes, as well in 2-D as in 3-D. As we know, the big advantage of Bezier curves is that submitted to affine transformations, the image has the same control points as those produced by the same transform over the initial ones. Just to mention it, we have to say that there is only a very small drawback in this object. And this "point-faible" is that it does not accept to be too small. For those cases, we have another object as will be seen.
9- This other version of Circle has two special reasons to be included in MG. The first one is to serve as the basis for the creation of the all-new object "spiral" from which we will speak later on. The second is to represent the simplest way of drawing circles according with MetaPost command "full circle", so with no limitations in small sizes and extremely simple to use as it is controlled like a right line. The price is the big limitations in relation with transforms, although a few are allowed to be used with the spiral.
10- In close relation with the button at its side it has been included the one represented here for the creation of spirals. This is a new object extremely versatile and simple to use. A must for this kind of figure. It is possible to draw spirals that go clockwise or anticlockwise, with the number of spires desired. It is also possible to select the final point in any position or angle. The spirals can be included inside a circle or an ellipse with the axis parallels to coordinates axis or rotated any angle. And, finally, this curve can serve also as the base of a written text in the same way as any other curve in METAGRAF.
11- This button corresponds to the general Bezier curve, open or close. It has been explained before and we will say more afterward, so we will not extend our comments as the users of METAGRAF know very well this nice approach to one of the strongest points of MetaPost. Nevertheless it must be said that this object maintains all its capabilities in 2-D and 3-D transformations.
12- The polygon is the typical object already known in other design applications and MG uses it in a standard way. In this BETA version, its ease of use has been increased from 2-D to 3-D, in such a way that the retouching of its shape through the corner points has been maintained in any situation. Everything related with this object can be applied to the Poly-Line one.
13- The simplest object is the point. Although simple it is useful in certain situation as will be explained later on in relation of positioning of final images. Also, changing the pen thickness it is possible to draw nice totally filled small circles absolutely perfect as we have shown in a chapter before.
14- The object ARC has suffered a certain modification to simplify its use. This new version is just what we were looking for. Simple and very intuitive with no limitations if the user tries it he will be convinced of its simplicity and incredible capability regarding edition of the figure, placements of arrows and so on. The interesting point is that the arc is always drawn from the second point to the third in an anticlockwise direction. Knowing that, any arc can be drawn quickly and easily and if arrows are wanted, the direction is known.
We finish here this chapter in which all the MG-standard object-buttons has been explained and its relationship with the available functions clarified..