GIMP Version: 2.6.11
Operating System: Windows
OS Version: 7 pro
GIMP Experience: Intermediate Level

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I know there has to be a simple way to fix this but I haven't found it yet. I've attached an example to help illustrate it. When I make a polygon, in this case a rectangle, then grow the selection the corners are rounded, as seen in the white layer. I don't have rounded corners turned on and even if I did I have it set to 0. Is there a setting I've been overlooking or is this just a gimp quirk? BTW I'm using 2.8, not 2.6.

This happens to me too in 2.6.11. It's a nuisance but I don't know if there is any way to correct it.

Growing or shrinking a selection works, not by scaling the selection (which would be problematic in most situations) but, by painting around the selection's perimeter (its marching ants) with a round brush*. This results in a rounding of corners when a rectangular selection is grown.




* The actual algorithm is a little more complicated since it tries to retain any feathering that might exist in the original selection, but for the purpose of understanding why the corners get rounded when a selection is grown, this explanation should suffice.

Saulgoode explains a trick for this in this thread, just tried it and it works
from the thread..
A good way to correct for this is to, in the case of growing an elliptical selection, clicking within the grown selection with the Elliptical Select Tool. This will cause the resizing handles to appear. Move the mouse to the top resizing bar and then press the cursor left key on your keyboard*. This will result in a "new" elliptical selection that is the same size as the original, but with the distortions caused by growing eliminated. Click in the center of the selection (or press ENTER) to accept this corrected selection. (A similar operation can be used for rectangular selections, only with the Rectangle Select Tool.)


* Alternately, you can place the mouse pointer over either of the side resizing bars and use the up or down cursor key -- the idea is to not actually resize the selection, but to "trick" GIMP into thinking you have.

view topic

You could also resize from the center and use the dialog box to precisely change size in GIMP 2.8



or turn into a path and move the handles manually

Alan

Another alternative would be to use the [stroke path] [Line Style] [Join Style] [Miter]



this would work on many different angles and not just 45 degree corners.

I've started just making 4 guides around the edges and drawing another rectangle, I'll try the other ideas mentioned. I was thinking it was just me doing something wrong.

Here is a .scm I wrote (long ago) that can help do what you want. http://www.silent9.com/incoming/scripts ... tional.scm It creates eight menu items under Select>Directional Grow>Grow Left (right, up and down, left 10, right, 10 etc.) The alt-cursor keys are not used in gimp, so you can use Edit>Keyboard Shortcuts to set them up. Here is a screen grab of the keybindings I set up:



SO to grow all directions by one pixel, just use (hold the alt key) and cursor up, down, left, right. or by 10 pixels (hold Shift-Alt) and cursor up, down, left, right.

-Rob A>

rob a: that looks like a very helpful script, i'm going to try it out at once!
(i'll be very careful with the alt+up commando though - who knows what it will do to my taste in clothes and music )

I grabbed it, Rob. Thanks