(defun lerp-gl-array (a b c count interpolation-factor)
(dotimes (i count)
(setf (gl:glaref c i)
(alexandria:lerp interpolation-factor (gl:glaref a i) (gl:glaref b i)))))
is this my fault? Any idea how can I improve performance?
Another problem is that the compiler doesn't know what types the values are, so has to call generic math routines instead of using CPU ops directly.
Storing the source arrays as specialized lisp arrays, and declaring types (and/or check-type) would help with both problems, though writing to the gl-array would still be slow until that bug is fixed. You could work around the bug by using cffi:mem-aref directly instead of glaref, or if you are using shaders, you could just do the interpolation on the GPU.