Caustics effect

[MartinDRChacon]

Ported from:
https://github.com/ajmas/JH-Labs-Java-Image-Filters/blob/master/src/com/jhlabs/image/CausticsFilter.java

As mentioned here by Mr. Ramos : #1464 (comment)

[cameronwhite]

Very cool, thank you for working on this!

I likely won't have time until later this week to review more closely, but one initial thought is that maybe we can reuse / extend the existing PerlinNoise.cs to be reusable here?

[MartinDRChacon]

I think both algorithms aren't compatible. The one used by Caustics effect hat Three coordinates and is seeded. On the other hand, PerlinNoise has only two coordinates (PointD) and is static. But I removed some redundant methods.

[cameronwhite]

I think this likely also should be converting the ColorBgra to premultiplied alpha since the Cairo ImageSurface pixels are premultiplied (see #1553 - it's very easy to get this wrong currently)

The algorithm may also need some adjustments for this - right now the brightness parameter makes the pixels more opaque if the palette color is transparent.

[MartinDRChacon]

bf4cbff - Please refer to this commit. That is where I tried to address this. :)

[cameronwhite]

This label feels a bit confusing to me since we don't have a way to create an animated effect out of this.
Maybe something like Time Offset or just Offset? To indicate that it's shifting the noise pattern around

[MartinDRChacon]

I just changed the caption and property to TimeOffset.

[cameronwhite]

Naming-wise, perhaps something like PerlinNoise3D? I worry that ClassicNoise might be too generic

[MartinDRChacon]

I just changed the name :)

[cameronwhite]

Thanks for the changes!

I think there still is something off with the alpha handling. For example, if I have the foreground color set to FF000032 in the color picker (which is unpremultiplied, the premultiplied color would be 32000032, and have the brightness set to 100, then it produces many fully opaque white pixels FFFFFFFF. I would have expected the result to be something like (premultiplied) 32323232 to have white pixels with the same alpha

[MartinDRChacon]

In the previous commit, the waves always had an alpha value of 255. If I understand correctly, you want the waves to have the same transparency as the background color, but this would make it harder to draw the waves over the picture like in the following example:

The changes were made in the following commit: [f355c87]

But they were reversed in commit: [463c759]

You could accept or discard the last commit. I am open to any other feedback or question. :)

[cameronwhite]

Thanks :) I agree that behaviour would be useful, but perhaps there could be another option or way of achieving it?
I just think it's very surprising if a brightness control affects opacity - e.g. having to set your primary color to transparent in order to get opaque white caustics on a transparent background doesn't seem the most intuitive