I had an idea of a program for creating textures and am wondering if there exists software that can accomplish it.

The idea is a program that will draw to a diffuse, specular, bump, or any other layer simultaneously when using a brush tool. So the basic use would be like this. I could configure the brush tool to draw metal. It would draw on separate layers the different light reflection properties of metal. I could then draw rust onto that metal and it would automatically make those parts less reflective. Or be able to draw dents, scratches, or other imperfections and have it update the bumpmap, color and reflective properties automatically.

This idea could be extended to other materials as well. Starting with wood then burning the world, adding mold, adding a seperate layer set to overlay polish over the wood.

Start with concrete, add mold, or paint.

Really the possibilities are endless.

What I want to know is if there is an existing tool that can do this or if a tool, such as photoshop or gimp, can be used in this way to accomplish the same thing.

Yep. Photoshop can. User Made presets are often used to create certain textures such as wood or metal.

I've wondered about that, too, but that would probably be some rather complex code. You also would want different values for the brushes for the normal map/spec map, too. The way I handle it is to paint either the height or diffuse map first and keep everything in as many layers as I need. Later on, converting the diffuse map to a height and spec map is only a matter of desaturating the layers and adjusting the brightness and contrast. With some practice it works pretty well.

Yep. Photoshop can. User Made presets are often used to create certain textures such as wood or metal.[/quote]
I don't actually know if it can simultaneously use a paintbrush that when painting paints to 3 separate layers of normal, diffuse, specular.

Even if it actually can, I have NEVER seen an art video do that. When generating normal maps, nobody uses the default brick texture normal map or scratches. The always use zbrush, scrap their metal and generate the normal map from an extremely high poly. Nobody ever (well I do a lot) but no pro artists will paint normals in the texture, they will make the 3D geometry to bake instead. There is also never just a 1 pass thing with artists, they will tend to tweak the specularity to different colors and what not to get their model exactly perfect. Artists are freaks about perfection.