I often came across textures in which transparent pixels are replaced by the continuation of adjacent more opaque ones. Is there any program that does this automatically from transparent textures? I hope some command-line tool? And how is this technique generally called? Because I understand I need this now, but I can not find any information. Thanks!
Some engines like Unreal will do this for you; importing a texture with a alpha does that.
Unity has a manual way: https://docs.unity3d.com/455/Documentation/Manual/HOWTO-alphamaps.html
You can do it on your own using Gimp or any 2D tool that supports alpha. Gimp even has tools like displacement that makes this easy, but blur also works.
Any texture baking software has this option: XNormal (Free), Substance, Quixel, Blender (Free), 3Ds Max, Zbrush, Maya, etc...
A quick search for Substance alternatives gives me this: https://www.slant.co/options/12608/alternatives/~substance-painter-alternatives
It's one of those things that has many names but "Alpha Texture Edge Padding" or "Texture Edge Padding" should work for search results. The problem is that each software likes to call this something else.
I had to implement this a year ago. If you want to do it yourself, the basic idea of how I did it was pretty simple. Just go through the pixels of your image, and for each pixel that has zero alpha, set the colour to the nearest non-zero alpha pixel. You could use euclidean distance, manhattan distance etc.
Note that this is pretty slow, you will probably want to optimize it if you are using bigger textures.
Here is a thread on optimization:
