*scratch*.el

;; In a clean image:

(ql:quickload :shadow)

(shadow:defstruct-gpu sprite-index ()
  (image :sampler-2d :accessor image)
  (sprite :int :accessor sprite))

(shadow:defstruct-gpu sprite-sheet-data ()
  (x (:float 4) :accessor x)
  (y (:float 4) :accessor y)
  (w (:float 4) :accessor w)
  (h (:float 4) :accessor h))

(shadow:defun-gpu sprite/vert ()
  (values))

(shadow:defun-gpu sprite/geom (&uniform
                               (model :mat4)
                               (view :mat4)
                               (proj :mat4)
                               (tex sprite-index)
                               (sprite-sheet sprite-sheet-data :ssbo :std-430))
  (declare (output-primitive :kind :triangle-strip :max-vertices 6))
  (let* ((mvp (* proj view model))
         (extents (vec4 (aref (x sprite-sheet) (sprite tex))
                        (aref (y sprite-sheet) (sprite tex))
                        (aref (w sprite-sheet) (sprite tex))
                        (aref (h sprite-sheet) (sprite tex))))
         (size (.xyxy (texture-size (image tex) 0)))
         (offsets (* size (vec4 (* 0.5 (.zw extents)) (* -0.5 (.zw extents))))))
    (setf (.zw extents) (+ (.xy extents) (.zw extents)))
    (emit ()
          (* mvp (vec4 (.xy offsets) 1 1))
          (.xy extents))
    (emit ()
          (* mvp (vec4 (.xw offsets) 1 1))
          (.xw extents))
    (emit ()
          (* mvp (vec4 (.zy offsets) 1 1))
          (.zy extents))
    (emit ()
          (* mvp (vec4 (.zw offsets) 1 1))
          (.zw extents))
    (end-primitive))
  (values))

(shadow:defun-gpu sprite/frag ((uv :vec2)
                               &uniform
                               (tex sprite-index))
  (let ((color (texture (image tex) uv)))
    color))


;; boom
(shadow:make-shader-program sprite-shader (:version 430 :primitive :points)
  (:vertex () (sprite/vert))
  (:geometry () (sprite/geom))
  (:fragment () (sprite/frag :vec2)))