GIMP Script: Sample a Gradient along a Path

When I try to use the script with a generated Circle or Sine Wave shape created by the Shape Paths script I get the following 2 errors:

Error #1:
Plug-In 'Sample Gradient along a Path' left image undo in inconsistent state, closing open undo groups.

Error #2:
Error while executing
(script-fu-sample-gradient-along-path 3 14 17 25 3 TRUE "Circle Gradient")
Error: Procedure execution of gimp-image-pick-color failed

For Circle, my image was 400 X 400, I had the shape set to 200 for X, 200 for Y, Radius 200, and Stroke Path check box checked.

In the Sample Gradient along Path dialog I kept all the defaults but changed the Gradient Name to "Circle Gradient".

The resulting Gradient does not look like the example posted here. The gradient created appears to to have the first 25% go from gray to white and then the remainder 75% restarts to gray and goes to white until the end of the range.

Does anyone know how to fix this?

Hello Rob,

I am still getting error messages with the Circle shape setup the same way as described in my previous post. I have made sure that the updated script is copied to the correct location and unloaded and reloaded GIMP. The Sample Gradient along a Path script copied to the GIMP script area is 5,169 bytes in size.

I am using GIMP 2.6.8 on a Windows 7 64 bit system. By the way, in my previous post I was using GIMP 2.4 on a Windows Vista 32 bit system.

I noticed that the Sample Gradient along a Path Message is a bit different probably because of the new version of the script.

I am getting the following 2 errors and they both appear to pop up at the same time:

#1 - GIMP Message
Plug-In 'Sample Gradient along a Path' left image
undo in inconsistent state, closing open undo groups.

#2 - Sample Gradient along a Path Message
Error while executing script-fu-sample-gradient-along-path:
Error: Procedure execution of gimp-image-pick-color failed

I took a look at the script and see a semi-colon in front of an ELSE statement. I do not know GIMP script programming, but by looking at the rest of the code it appears the semi-colon is used as a comment. Should this ELSE statement have been commented out? Below is the code.

(if (= inSmooth TRUE)
(gimp-gradient-segment-set-right-color varGradient varCounter (car (gimp-image-pick-color img inLayer (max (min (list-ref varNextPos 0) varWidth) 0) (max (min (list-ref varNextPos 1) varHeight) 0) TRUE TRUE inRadius)) varNextAlpha)
;else
(gimp-gradient-segment-set-right-color varGradient varCounter (car (gimp-image-pick-color img inLayer (max (min (list-ref varPos 0) varWidth) 0) (max (min (list-ref varPos 1) varHeight) 0) TRUE TRUE inRadius)) varAlpha)
)

I am also getting the following errors when using the Sine Wave shape. The Sine Wave is my goal to use with your script. I plan to use the gradient to make a gradient image I will use as a displacement map in Lightwave 3D in order to bend a 3D object into a wavey pattern. I was using the Circle shape as my first test since your description example uses the same shape.

I am using the following settings for the Sine Wave on a 640 X 400 image.

Start X: 0
Start Y: 200
Amplitude: 200
Wavelength: 1
Number of cycles: 1
Stroke Path check box checked.

Also, my brush size is 1 pixel.

I am using the default options in the Sample Gradient along a Path script when trying to apply it to the Circle or Sine Wave shape.

Thanks in advance for taking a look at this. If there is anything I can do to help debug this problem let me know.

Ralph Ocampo

Hello Rob,

I did some research and discovered that the semi-colon in front of the else was just a typical editing method to show where the else part of the if condition starts. Apparently an else key word is not needed in this scripting language.

By the way, in my previous post the Sine Wave "Wavelength" value should have been 640 not 1.

I have experimented further and can get the Circle and Elipse shapes to work only if I bring in their dimensions by 1 so the shape does not touch the edge of the image.

For the Sine Wave I set "Start X" to 1, "Amplitude" to 199 and "Wavelength" to 638. As a result, I was able to around the problem with the Sine Wave.

Thanks for the script. I will now use the custom gradient to bend my 3D objects into wavy objects.

Ralph Ocampo

Hello Rob,

I have another note about the work around. When I had set the path for the Circle and Sine Wave to be 1 pixel in from the border I noticed that the gradient that contains the white portion of the spread had a gray band right in the middle where I expected pure white.

I believe the problem is the "Sample Average Radius" value not being clamped. Currently your default value is 3. I believe what is happening is that with the value of 3 the sampling extends below the bottom of the image. I assume that when this happens the value used for the sample average becomes zero (black) for some of the pixels around the sample point. This may also explain why I do not see a problem when the path is near the top of the image because the top of the image is already black and averaging in a bit more black (zero) to black has no effect.

I resolved the problem by making sure the path was created more than 4 pixels from the edge of the image. I also experimented with the "Sample Average Radius" value and lowered it to 1, the lowest value. Doing so would only help if the path was more than 2 pixels from the edge of the image. I hope this makes sense.

If you would like me to send you and example image let me know.

Ralph Ocampo