Looking for GIMP tutorial for bending a shape around an arc

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Azhrei
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Looking for GIMP tutorial for bending a shape around an arc

Post by Azhrei »

Hello everyone!

I know we have some graphics experts here, so I'm hoping someone can either give me a quick hint as to where to look in the GIMP UI, or perhaps could point me to an online tutorial.

I have a round tower -- about 60 feet across on the inside -- that I need to put a short section of stairway into. Along the east wall, the stairs should cover about a 45-degree arc.

I have Jonathan Roberts' image of a stairway that is rectangular, so I need to bend it so that it will fit nicely against the inside wall. So far, I haven't found a way to do this. I checked out the Shear and Perspective tools, but they produce a straight edge and I need a curved edge.

I expected to be able to draw a path using a b-spline and then attach one edge of the stairway image to it and have it bend, but no luck.

Any help would be very much appreciated! Thanks!

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Post by Phergus »

One way that comes to mind would be to use the Polar Coordinates filter under Distorts.

Start with an empty square canvas the inner diameter of the tower.

Size the stairs to fit across the top and to have the appropriate width then paste it into the empty canvas. In other words it should occupy the equivalent of 5' or so of the total 60'.

Apply Polar Coordinates filter to image and adjust parameters to suit.

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Azhrei
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Post by Azhrei »

Thanks, that looks doable. I had played around with the Polar Coords filter before but didn't understand the mapping. Your explanation was the clincher. :)

For anyone else interested in doing this, I only wanted my stairs to occupy about a 45-degree angle -- about 1/8th of a full circle -- so my stairway shape across the top of the canvas should occupy only 1/8th of the canvas width.

I'll be playing with this some more to get something that looks good. Thanks again. :)

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torstan
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Post by torstan »

I never knew how to do that. Thanks for the tip Phergus. I've had a play and it works out really well. Azhrei, post an example when you're done - I'd like to see how my stairs worked out!

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Post by Phergus »

Glad it was useful.

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