Hello.
I have been trying to create terrains in quite old software called Bryce. When exporting, the textures look terrible, screenshots below.
How do you generally create terrains? Is there a shader that works off 2d or 3d texture to color a pixel based on slope-altitude-uv? Do you get 3d artists to hand paint textures? Is there some other way?

    What you get out of bryce should be used as splatmaps or masks and the issue here is the resolution then of the textures you blend between with these masks. Those textures should be tiling so as to get around the resolution issue.

    It also looks like there might be some compression artifacts in there but I'm not entirely sure.

    PeterSmith How do you generally create terrains?

    From natural data, with noise or fractal functions, or modelling natural processes.

    PeterSmith Is there a shader that works off 2d or 3d texture to color a pixel based on slope-altitude-uv?

    Yes. That's done in the vertex stage. Altitude is available directly from the height map texture, slope via lookup of neighbours needed to calculate the slope.

    PeterSmith Do you get 3d artists to hand paint textures?

    Nope. Can't pay them ... but there's a plethora of free textures also for PBR workflows on the internet.

    PeterSmith Is there some other way?

    Texture splatting or procedural colouring are ways to clad height maps. But height maps aren't the only way to model terrain. They do the visible surface without cavities or too steep slopes.