;;;; wh-engine/render/shader.lisp
;;;; Lisp class for holding & handling shaders.
;; (in-package wh-engine/render)

(defun replace-cross-referenced-vars (forms vars replace-fun)
  (loop for elt on forms
        for form = (car elt)
        if (symbolp form)
          do (let ((var-entry (find form vars :key #'car)))
               (when var-entry
                 (rplaca elt (funcall replace-fun var-entry))))
        else if (consp form)
               do (collect-cross-referenced-vars (cdr form))))

(defun transpile-shader (name &key
                                version
                                ((:in vert-inputs))
                                ((:inter inter-vars))
                                ((:out frag-outputs))
                                ((:uniform uniform-vars))
                                ((:vert vert-body))
                                ((:frag frag-body)))
  "Translate Lisp shader code to GLSL."
  (list (collect-shader-vars vert-body)
        (collect-shader-vars frag-body)))

(defmacro define-shader (name (&key
                                 ((:in (&rest vert-inputs)) ())
                                 ((:inter (&rest inter-vars)) ())
                                 ((:out (&rest frag-outputs)) ())
                                 ((:uniform (&rest uniform-vars)) ()))
                         &key
                           ((:vert (&body vert-body)))
                           ((:frag (&body frag-body)))
                           version)
  "Define a GLSL shader with Lisp code."
  `(defparameter ,name (transpile-shader ',name
                                         :version ,version
                                         :in ',vert-inputs
                                         :inter ',inter-vars
                                         :out ',frag-outputs
                                         :uniform ',uniform-vars
                                         :vert ',vert-body :frag ',frag-body)))