Populating on an Alpine Shader will definitely be slower. It's a more complex and demanding shader to calculate than, say, a Power Fractal (generally speaking), or a DEM (which is just a simple height value lookup in a 2D raster data set). The Populator has to sample the shader it's sitting on in order to find the position for each instance, so the simpler the underlying shader, the faster populating will be. I don't know exactly how much slower it would be than a DEM, but I would guess up to 10x, unfortunately. That's just the nature of procedural vs. pre-calculated raster terrain - a procedural terrain literally involves a "procedure" to generate each point, whereas DEMs and other basic heightfields are static, it's just like determining a pixel value in an image you've loaded.
You can consider using other procedural shaders in place of the Alpine Shader, or if possible in your scene you could generate a heightfield *from* the alpine shader *just* in the section of terrain where you need to populate (unless you're populating to the horizon), then use that heightfield for the populator, and use the normal Alpine Terrain for the rest of the background mountains.
- Oshyan
