How to draw concave and convex shapes

[BBking]

Hi there,

Just wondering if I could get any tips of drawing shapes. I asked this question over at graphics exchange here: http://graphicdesign.stackexchange.com/questions/27221/illustrator-how-to-make-lens-elements-convex-and-concave-shapes but it was regarding only Illustrator.

I can't even seem to draw a straight line in Inkscape!? I use the  but after one two points, it wants to draw another curved line...? I'd like it to snap and come straight, like something simple in power point.

Cheers!

Blake.

[brynn]

Welcome to Inkscape Community!

Inkscape, much like Illustrator, is a complex and sophisticated program.  Some people seem to think Inkscape is easy to learn, others think it's hard to learn.  But I think it depends on your background, and what kind of experience you have with graphics.

After reading the message you referenced, and considering the question you asked here, it seems like you are hoping for a fast way to draw a complicated image.  And I'm afraid I don't have any fast answers.  I think you'll have to resign yourself to taking some time to learn how to use the tools you'll need.

I'm not familiar with power point, so I'm not sure what you want to do.  But I wrote a tutorial a while ago, when someone else complained about not being able to figure out how to draw a line.  The problem is that the answer is not simple, because Inkscape is so sophisticated.  But the good news is that because Inkscape is so sophisticated, it can do some amazing things.  You just have to take the time to learn.  So for what it's worth, here's that tutorial:  http://forum.inkscapecommunity.com/index.php?action=articles;sa=view;article=7.

And here's the short answer, for drawing a straight line.  With the Pen/Bezier tool, click once where you want the line to begin.  If you want the next node to be a sharp corner, click once on that spot.  If you want it to be a smooth corner, click, hold the mouse button down while you drag a short distance.  To be honest, I find it hard to control the curve that way.  I usually draw only straight segments, then I come back and adjust the curves as I need them to be.  To end the line, double-click.

Referring to the title of your message, you could probably do that with the Ellipse tool.  Draw the ellipse the shape you need for the convex or concave curves, convert the ellipse to a path and then edit tha path as needed.  However, in using these few simple words, I'm skipping over many steps that are needed for node editing.

To get a good start with paths in Inkscape, I would suggest the Quick Start section of the manual http://tavmjong.free.fr/INKSCAPE/MANUAL/html/QuickStart.html  I think it's the 3rd or 4th tutorial about drawing a hiking club logo, that will give you the basics that you'll need.

And whenever you get stuck, we'll be glad to help.  Just post your specific questions 

[BBking]

Thank you so much! I eventually got something like this:



It was that double click that sorted me out! After that I could add path nodes and adjust.

The only other this, is that I was guess the node points. What I liked about the Illustrator solution, was that it was exactly symmetrical.

What I meant by "snapping, like in Power Point", to get a like exactly vertical, it give you a straight line, until about 10-15? then it'll slant and angle the line. So, right click and hold, drag down, move slightly to the right and it will stay exactly vertical until you move about 1cm (with the mouse) and then it'll angle.

Are there any solutions for what I'm after in Inkscape? Happy to be pointed to tutorials. 

[brynn]

Yes, if I understand, Inkscape has a way to do that.  After you set the last node (AI called "points"), press the Ctrl key, that will constrain the placement of the next node to perfectly vertical or perfectly horizontal (from the last node), depending on where you're moving the mouse.  And if you move the mouse around in a circular motion, it sort of snaps to 15 degree angles, as you move it around.

However, if you need this lens to be symmetrical and precise, I would suggest another way of drawing it.  Because even with snapping and all Inkscape's great stuff, it would be hard to make it symmetrical by drawing with the Pen/Bezier tool.

For me, I would probably use the Ellipse tool, convert to path, and use node editing.  Or there probably would be a way to do it with path operations (although perhaps very slightly imprecise).

[BBking]

Thanks so much for your help! Really appreciate it.

When you say eclipse tool, do you mean something like this:




How do I then "bow" it? Like, picking a centre point and dragging it left/right while anchoring the top/bottom points?

[brynn]

Yep, can do 

I can't tell for sure what you've done to create the bottom object.  But if it's what I think, the nodes are already in place, so you don't even have to add more.

From the bottom object, which is selected with the Selection tool, in that screenshot, switch to the Node tool.  Hopefully there are 4 nodes, and hopefully the 2 in the middle (not top and not bottom) are centered between top and bottom.  Now just select those 2 middle nodes, and you can move them only, without moving the others.

Multiple selection:  2 ways:  Click 1 node, hold Shift key while you click the other one.  Or using the Node tool, drag a selection box around those 2 nodes.

To move horizontally (or vertically), use arrow keys (or other more complex means):  Arrow keys move nodes by a 2 pixels step with each keystroke.  Use Shift + arrow to move 10 times the step distance.  Use Alt + arrow to move by half step at a time.  The step distance can be changed in Inkscape Preferences,  if you have some need to change it.

Or if you need to move the nodes by some specific amount, you can use the X and/or Y fields on the Node tool control bar.

And I'm guessing you'll want those nodes to be smooth nodes.  If they aren't already smooth, you can change them while they are selected (this button on Node tool control bar  )  (or possibly you'll want to use symmetric nodes, this button  )