Strange margin defects occuring with the egg-palettize tool

[nosyliam]

I've been using egg-palettize to group textures but there's just one issue I can't solve. Whenever, I create a palette that has the margins option on, it results in a very odd pattern around the texture. All my textures are 24-bit PNGs.

This is my .txa file:

:background 0 0 0 0

* : force-rgba linear clamp_u clamp_v rgb,rgb best
:margin 10

*.egg :

I'm also running it with -opt and using eggs made by egg-texture-cards which has the "-f rgb" option. I've been trying to find a solution for this for quite a while now, if anyone knows why this is occurring a fix/workaround would be appreciated.

[rdb]

Could you attach the source files we would need to reproduce the issue?

[nosyliam]

I would very happy to do so privately. Do you have any other ways to contact?

[rdb]

Contact me at git@rdb.name.

[nosyliam]

I have sent an e-mail with the files to git@rdb.name. Please let me know if you do not receive it.

[rdb]

So here's what's happening: since you set it to clamp mode, egg-palettize is stretching out the colours at the edge of the texture into the margin area, with the intent to reduce artifacts when you use this texture with the "clamp" texture wrap mode. Otherwise, when the texture is sampled in "clamp" mode, you may end up with a darkened border due to the filtering sampling into the margin area.

This seems to be working as intended, as far as I can tell from the files you sent; the weird colour in the margin area is just a repetition of the colours at the edges of your texture. If you change it to "repeat_u repeat_v" instead, then you'll see it wrap around instead. Note that even transparent pixels can have a colour value.

If I open the texture in the GIMP, first paint a 1-pixel border outside the texture with black (to clear the colour information) and then erase it to make it transparent, then there is no extension of the texture border in the margins. (Clearing it with black first is optional, but since egg-palettize does not premultiply the alpha, it means that you are still seeing the colour value in the .png, even though it's masked out by the .rgb that contains the alpha mask.)

Is that what you're expecting—to see only the background colour in the margins instead? It would not be very difficult to add such a feature, if you would request it. If not, and if the above is sufficient to solve your problem, please close this issue.

[nosyliam]

I was originally only expecting it to make a margin with the background color, not to extend it. I've actually been making 5-pixel transparent borders on all my images manually beforehand but it's a very tedious problem that I was hoping the margin feature could solve. I'll request it as a feature in another issue, thank you :)