Composite Overlay Amount reset

[davidh]

Loading an Overlay image always resets Overlay Amount to 100%.

[jsachs]

That is by design -- what do you think it should do?

[davidh]

If you load an overlay image, find the right setting of the Overlay Amount, but then or sometimes later replace the overlay image with another one, the Overlay Amount is reset to 100%. I would expect to stay as it was.
By the way, if you load a solid color instead of an image, the Overlay Amount is not reset.

This is not a problem in Composite, perhaps just a little inconvenience if you loose the setting and have to search for the previous Overlay Amount again because you have not first checked it before changing the Overlay image.

However I see the same design is used in Stack Images Amount control and with that number of images that can be stacked it is nearly impossible to remeber each of the Amount settings once you start editing, reloading etc.

Resetting the Amount (any Amount) to 100% manually is easy as it is one of the two extremes, but any setting in between has to be remembered.

[jsachs]

The problem is the overlay mask which will only work on a certain size overlay image. Once the overlay mask is cleared (which is currently always done when switching overlay images), there is no way to preserve the two slider settings since it switches back to a single slider.

There are a lot of possible cases with all the combinations of old and new overlay image and mask or no mask:

Old: solid color overlay / overlay image; has mask (double slider) or has no mask (single slider)
New: solid color overlay / overlay image

If both old and new are images, they may or may not be the same size.

[jsachs]

I tried to analyze all the possible cases and I think there are just two: either the overlay amount control has a single slider or it has a double slider (i.e. there is also an overlay amount mask), before switching overlay images.

If there is a double slider, the Overlay Amount mask gets reset and the slider becomes a single slider at 100% (just as it does now). Even if the images were the same size, It would be very complicated and error-prone to try to preserve the double slider position as this implies retaining the mask as well, and the mask would need to be recalculated as it might depend on the contents of the image.

If there is a single slider, its position can safely be retained. Switching images, since it resets the mask, always reverts to a single slider.

This seemed to work OK when I implemented it in Composite. Similar code also exists in Layout, Repeat, Stack Images and Wave, but the changes should be easy to extend to these other transformations.