Filter Preview is Blank

Here is the filter I used.

Lua Test Lissajous Lines - Optimsed Lines.ffxml

Yes, I have tried this with varying success. With this filter it works with 96x96 images but not with larger ones. I do know there is a bug in my code which I have to resolve. When the preview is linked to a specific component I was expecting it to show that component and not the final image.

However, in some other filters where the code is correct and the original image is drawn correctly the preview is sometimes not drawn or partly drawn. The final image is correct when not in edit mode. The preview seems more prone to go wrong when the compute time in the prepare() section is long.

Due to get_sample(x, y) working pixel by pixel which does not work well with a collection of vectors I am preparing a computationally heavy optimising routine that breaks the set of vectors down into small manageable groups that only needs to be computed once no matter what size the final image is or whether it is the 96x96 image used in the editor. Currently my code is using the Liang-Barsky algorithm to chop up the vectors. This works. In the new version I am trying a simpler approach which should give better response times. Initial testing indicates a reduction of the get_sample(x, y)compute time from 50 seconds down to around 2 or 3 seconds on a 400x400 image. However, because the prepare() function runs multiple times this computational heavy routine runs N times when only once is necessary which slows things down a lot. These seem to run in parallel threads. So the non-display of the preview might be some sort of race condition. I don't know how to force the prepare() function to run only once which is what I expect it to do.

Thank you. I am already using scaling using OUTPUT_WIDTH and OUTPUT_HEIGHT in the code in several places. I still have a logic bug to fix though as my new algorithm results in some "holes"

This does not sort why the preview is not always drawn though. As written before I have seen this in several more complex filters.