I am just trying out a simple wave effect using a rectangular water body as a costume, and for some reason the change whirl effect script doesn't work! The minute i add a background color or just another color block in the costume then it works magically? How do I add a smooth wave effect without adding any background color in the costume as I want to add other Sprites ( layered) .

Any help much appreciated

It would help if you shared the project. Guessing what you are doing then the whirl effect only acts on the sprite's costume. It doesn't whirl the image behind the sprite.

Refer to the project -https://scratch.mit.edu/projects/103570634 .
costume2 doesn't work why?

in costume3 when i add another small rectangle then whirl effect works!

many thanks

Ok can see what the issue is now. The costume doesn't whirl because it is a solid colour so although the pixels move they are all the same colour and so you can't see anything. You have offset the costume centre though so you are assuming the costume should contain transparent pixels, however it won't as the costume centre is really just a translation. By adding the rectangle then you force the costume to contain transparent pixels which can then be whirled.

SeagullCC wrote:

Refer to the project -https://scratch.mit.edu/projects/103570634 .
costume2 doesn't work why?

in costume3 when i add another small rectangle then whirl effect works!

many thanks

The whirl effect is limited to inside the boundaries of the sprite it is applied to. The edges of the sprite are respected. If you apply it to a rectangular sprite of one color, then the effect has no effect. Put some detail inside your sprite it see the effect.