Splatmap performance question

When using multiple splatmaps, how much of a performance hit does the game take? Is it noticeable on most PCs (less then 10 years old, probably less then 5) or is it grave? Also, is the performance hit linear (2x splatmaps = double the generation time for splatmaps as before, 3x splatmaps = 3x), or exponential (2x splatmaps = 4x generation time, 3x splatmaps = 12x, etc)?

At least in the terrain shader, the splatmat is a control texture where the r, g, b and a chanels are used to store the alpha values of the four textures which will actually be combined. The terrain shader always combine four textures, even if you don’t define all of them - the undefined textures use default values. If you define more than 4 textures, than a second splatmap will be used, which will double the rendering time. In a rough approximation, the time taken will be proportional to INT(numTextures/4)+1

I’m not quite sure what you mean by performance, but probably FPS.
And I’m not quite sure what you mean with using multiple splatmaps. So I assume that you want to use them on different objects and not multiple splatmaps on one.

A splatmap is a texture, which needs 3 extra textures for each color (R,G,B). So when using a splatmap on an object, the shader needs to do 4 texture look-ups. Also, your GPU has to accept 4 textures from a material, which all have to be sent through the bus of your pc.

Your GPU shouldn’t do too many texture switches. So reusing textures is a good thing. Don’t try to make all your objects splatted. It would be a better thing to bake one good texture for the object.

We could state that, using one extra splatmap with different textures to splat is: extra splatmap = 4 extra textures, so it has a linear function of y = 4x in performance. But you will not see this in your FPS counter. You should look to ms/frame instead. This gives a better indication of your drawing. Turn on the stats in your game view to see the number of draw calls and texture switches.