;;;; wh-engine/render/view.lisp
(in-package wh-engine/render)

(defclass view (component)
  ((render-pass :documentation "The render pass this view should be drawn in."
                :reader render-pass
                :type fixnum
                :initarg :render-pass
                :initform 0)
   (render-mask :documentation "Only include actors with at least one of these tags."
                :accessor render-mask
                :type (proper-list symbol)
                :initarg :render-mask
                :initform '(:default))
   (cull-p :documentation "Whether or not to skip rendering out-of-frame objects."
           :accessor cull-p
           :type boolean
           :initarg :cull-p
           :initform t)
   (render-target :documentation "The render target this view renders to."
                  :reader render-target
                  :type (or render-target null)
                  :initform nil))
  (:documentation "Defines a view into the scene, and rendering settings for objects drawn by the view."))

(defmethod (setf render-pass) (new-val (this view))
  "The render pass this view should be drawn in."
  (setf (o! this :slot render-pass) new-val)
  (sort-world-views))

(defmethod resume :after ((this view))
  (unless (o! this render-target)
    (setf (o! this :slot render-target) (new! render-target :width *view-width* :height *view-height*))))

(defmethod activate :after ((this view) &key)
  ; Register
  (when (o! this actor tree-active-p)
    (pushnew (make-weak-pointer this) *world-views*)
    (sort-world-views)))

(defmethod destroy :before ((this view))
  (unless (o! this destroyed-p)
    ;; Unregister
    (setf *world-views* (delete this *world-views* :key #'weak-pointer-value))
    ;; Destroy buffers
    (when (o! this framebuffer)
      (gl:delete-framebuffers (list (o! this framebuffer))))
    (when (o! this render-texture)
      (gl:delete-texture (o! this render-texture)))
    (when (o! this renderbuffer)
      (gl:delete-renderbuffers (list (o! this renderbuffer))))
    ))

(defmethod view-matrix ((this view))
  "The world-to-view-space transformation matrix for this object."
  ;; view-space = local-space, scaled by ppu, then offset so [-width/2..width/2] -> [0..width]
  ;; (Y+ is still up in view-space)
  (m* (mat *view-ppu* 0 (/ *view-width* 2)
           0 *view-ppu* (/ *view-height* 2)
           0 0 1)
      (o! this actor local-matrix)))

(defmethod world-matrix ((this view))
  "The view-to-world-space transformation matrix for this object."
  (minv (o! this view-matrix)))

(defmethod view-point ((this view) point)
  "Transform point from world space to view space."
  (declare (type vec2 point))

  (vxy-trunc (m* (o! this view-matrix) (vxy1 point))))

(defmethod render-view ((this view) drawables)
  "Render everything in this view, given all drawables in the world."
  (let ((view-matrix (o! this view-matrix)))
    ;; Apply view matrix
    (gl:matrix-mode :modelview)
    (gl:load-transpose-matrix (opengl-matrix view-matrix))
    (loop for drawable-ptr in drawables
          for drawable = (deref-pointer drawable-ptr)
          when (and drawable (ensure-live drawable))
            when (and (o! drawable active-p) (o! drawable actor tree-active-p)
                      (some (lambda (x) (o! drawable actor (has-tag x))) (o! this render-mask)))
              do (o! this (render-drawable drawable view-matrix)))
    ))

(defun transform-box (box drawable-matrix view-matrix)
  (with-vec2 (ax ay) (car box)
    (with-vec2 (bx by) (cdr box)
      (let ((box-a (vxy-trunc (n*m view-matrix
                                   (m* drawable-matrix (vec3 ax ay 1)))))
            (box-b (vxy-trunc (n*m view-matrix
                                   (m* drawable-matrix (vec3 bx by 1)))))
            (box-ab (vxy-trunc (n*m view-matrix
                                    (m* drawable-matrix (vec3 ax by 1)))))
            (box-ba (vxy-trunc (n*m view-matrix
                                    (m* drawable-matrix (vec3 bx ay 1))))))
        (values (vmin box-a box-b box-ab box-ba)
                (vmax box-a box-b box-ab box-ba))))))

(defun in-view-p (drawable drawable-matrix view-matrix view-box)
  "Determine if drawable is in the view defined by view-matrix and view-box."
  (multiple-value-bind (box-min box-max)
      (transform-box (o! drawable culling-box) drawable-matrix view-matrix)
    ;; If it's in view at all, either its top-right corner is >= bottom-left of view,
    ;; or its bottom-left is <= top-right of view
    (or (v>= box-max (car view-box))
        (v<= box-min (cdr view-box)))))

(defmethod render-drawable ((this view) drawable view-matrix)
  "Render drawable with the precomputed view-matrix."
  (let ((drawable-matrix (o! drawable actor world-matrix)))
    (when (or (not (o! this cull-p)) (in-view-p drawable drawable-matrix view-matrix
                                             (cons (vec2 0 0) (vec2 *view-width* *view-height*))))
      (gl:push-matrix)
      (gl:translate 0 0 (o! drawable actor z-layer))
      (gl:mult-transpose-matrix (opengl-matrix drawable-matrix))
      (o! drawable (draw this))
      (gl:pop-matrix))))