#|
  This file is a part of stoe project.
  Copyright (c) 2015 Renaud Casenave-Péré (renaud@casenave-pere.fr)
|#

(uiop:define-package :stoe/engine/mesh
    (:use :cl :cffi :maths :shader
          :stoe/core/utils
          :stoe/engine/gl-utils)
  (:export #:mesh #:vertex-streams #:faces #:make-mesh
           #:stream-array #:ctype
           #:vertex-stream #:attrib
           #:index-stream #:mode
           #:make-stream-array #:make-vertex-stream #:make-index-stream #:bsize
           #:render-mesh))
(in-package :stoe/engine/mesh)

(defclass mesh ()
  ((streams :initarg :streams :accessor vertex-streams)
   (faces :initarg :faces :accessor faces))
  (:documentation "Class for a single mesh."))

(defun make-mesh (&optional streams faces)
  (make-instance 'mesh :streams streams :faces faces))

(defclass stream-array ()
  ((array :initarg :array :reader raw-data)
   (ctype :initarg :ctype :reader ctype)
   (count :initarg :count)))

(defclass vertex-stream (stream-array)
  ((attrib :initarg :attrib :reader attrib)
   (stride :initarg :stride)))

(defclass index-stream (stream-array)
  ((mode :initarg :mode :reader mode)))

(defun make-stream-array (array ctype count stride)
  (make-instance 'stream-array :array array :ctype ctype :count count :stride stride))

(defun make-vertex-stream (array ctype count attrib stride)
  (make-instance 'vertex-stream :array array :ctype ctype :count count :attrib attrib :stride stride))

(defun make-index-stream (array ctype count mode)
  (make-instance 'index-stream :array array :ctype ctype :count count :mode mode))

(defmethod size ((stream stream-array))
  (length (raw-data stream)))

(defgeneric bsize (object))
(defmethod bsize ((stream stream-array))
  (* (ctype-size (ctype stream)) (length (raw-data stream))))

(defun render-mesh (mesh program)
  (loop for stream in (vertex-streams mesh)
     with offset = 0
     do (let* ((ctype (ctype stream)) (size (size stream)) (bsize (bsize stream))
               (data (raw-data stream)) (attrib (attrib stream))
               (ptr (foreign-alloc ctype :count size)))
          ;; create the data for opengl
          (dotimes (i (length data))
            (setf (mem-aref ptr ctype i) (aref data i)))
          (let ((buffer-object (first (gl:gen-buffers 1))))
            (gl:bind-buffer :array-buffer buffer-object)
            (%gl:buffer-data :array-buffer bsize ptr :static-draw)
            ;; use it
            (let ((loc (get-location program attrib)))
              (gl-assert (gl:enable-vertex-attrib-array loc)
                         (gl:vertex-attrib-pointer loc 3 ctype :false 0 offset))
              (incf offset bsize)
              (foreign-free ptr)))))
  (let* ((faces (faces mesh)) (data (raw-data faces))
         (size (size faces)) (bsize (bsize faces))
         (index-object (first (gl:gen-buffers 1)))
         (ptr (foreign-alloc (ctype faces) :initial-contents data :count size)))
    (gl:bind-buffer :element-array-buffer index-object)
    (%gl:buffer-data :element-array-buffer bsize ptr :static-draw)
    (foreign-free ptr)
    (gl-assert (%gl:draw-elements (mode faces) bsize (ctype-to-gltype (ctype faces)) 0)))
  ;; cleanup data
  (loop for stream in (vertex-streams mesh)
     do (let ((loc (get-location program (attrib stream))))
          (gl:disable-vertex-attrib-array loc)))
  (gl:bind-buffer :element-array-buffer 0)
  (gl:bind-buffer :array-buffer 0))