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;; simple shader

(cl:defpackage 3bgl-ssbo-shader
  (:use :3bgl-glsl/cl))
(cl:in-package 3bgl-ssbo-shader)

(input position :vec4 :location 0)

(interface globals (:buffer t :layout (:binding 0 :std430 t))
  (foo :int)
  (mvp :mat4)
  (vec :vec4))

(defun vertex ()
  (setf gl-position (* mvp position)))

(defconstant +globals-binding+ 0)
;; `3bgl-ssbo` currently only supports hash tables for input data
;; but will support at least CLOS at some point, possibly `defstruct`.
(let* ((data (make-hash-table))
       (ssbo (3bgl-ssbo:make-ssbo :data data)))

  ;; store some data
  (setf (gethash '3bgl-ssbo-shader::vec data) (sb-cga:vec 1.0 2.0 3.0))
        ;; matrix slots currently must set from sequence with same
        ;; number of elements, but eventually should support filling
        ;; any size matrix from a 4x4 matrix
        (gethash '3bgl-ssbo-shader::mvp data) (sb-cga:identity-matrix)


;;; Get shader metadata while building shader stages:
  (multiple-value-bind (source uniforms attributes ssbos structs)
      (3bgl-shaders::generate-stage :vertex '3bgl-ssbo-shader::vertex
                                    :expand-uniforms t)
    (declare (ignore source attributes uniforms))
    ;; update the ssbo layout whenever the shader is recompiled.
    ;; :INDEX 0 tells it to use whatever buffer is at binding 0. Use
    ;; :NAME instead of :INDEX to specify buffer name directly.

    ;; in real code we would probably combine SSBOS and STRUCTS for
    ;; all stages in a shader program instead of just using one stage
    (3bgl-ssbo:update-ssbo-layout ssbo (3bgl-ssbo:calculate-layout
                                        ssbos structs
                                        :index +globals-binding+)))


  ;; main draw loop
  (loop
    while *looping*
    do
       ;; before using shader bind the ssbo, which also handles
       ;; creating/updating the buffer object in GL API
       (3bgl-ssbo:bind-ssbo ssbo +globals-binding+)

       ;; ... draw stuff

       ;; when updating data, flag ssbo as dirty so it will be
       ;; uploaded at next bind.
       (when (view-changed)
         (setf (gethash '3bgl-ssbo-shader::mvp data) (get-mvp-matrix))
         (setf (3bgl-ssbo:dirty ssbo) t))))