arbitrarily stretching a polygon shaped section of an image

[gimpuserjan2022]

hi ,
I am using gimp 2.10 on windows 10
I want to do the following
Select a polygon section in an image . I am able to do that using free select tool .
Now I want to select any vertex of polygon and pull it farther . This should distort the image inside that polygon . But when I do that simply the polygon shape changes but there is no effect on underlying image .
I hope that I am able to explain my requirement .
To give another example - suppose image is of human body . I draw a polygon such that right hand is inside it , now when I will stretch or squeeze the polygon then right hand should get deformed . 
Can you tell me how to do above ?
Thanks.

[programmer_ceds]

(01-22-2022, 01:08 PM)gimpuserjan2022 Wrote: hi ,
I am using gimp 2.10 on windows 10
I want to do the following
Select a polygon section in an image . I am able to do that using free select tool .
Now I want to select any vertex of polygon and pull it farther . This should distort the image inside that polygon . But when I do that simply the polygon shape changes but there is no effect on underlying image .
I hope that I am able to explain my requirement .
To give another example - suppose image is of human body . I draw a polygon such that right hand is inside it , now when I will stretch or squeeze the polygon then right hand should get deformed . 
Can you tell me how to do above ?
Thanks.

Try "Tools/Transform Tools/Cage Transform" it doesn't do exactly what you want as the stretched area doesn't reflect exactly what was under the boundary polygon but it may well be usable for you.

Select the tool, click where you want the vertices of the polygon to be - clicking again on the first one to complete/close the polygon. Then drag the polygon vertices until you have the desired effect and then press Enter.

[Zero01]

Another idea is to use the "Filters / Distorts / Curve Bend" tool
Not sure if this would be adequate, but it's the first thing that springs to mind, see example (click on picture for better view):

   

you may need to check / tick the 'Automatic preview' box..

[rich2005]

This using the cage transform tool as mentioned above
and an alternative using a Gimp plugin from http://www.gmic.eu the Warp (interactive) filter

about 2 min 30 secs https://youtu.be/FUfh3iWfcyM

This using the cage transform tool as mentioned above and an alternative using a Gimp plugin from http://www.gmic.eu the Warp (interactive) filter  about 2 min 30 secs