open-gl-boilerplate.lisp

#!/usr/bin/sbcl --script

;do something similar to 
(load "~/quicklisp/setup.lisp")
(ql:quickload :sdl2)
(ql:quickload :cl-opengl)


(defun debug-log (msg &rest args)
  "Output and flush MSG to STDOUT with arguments ARGS"
  (apply #'format t msg args)
  ;; Flush to standard out
  (finish-output))


(defvar *vs-source*
  "#version 330 core
in vec2 c2d;

void main()
{
    gl_Position = vec4(c2d.x, c2d.y, 0.0, 1.0);
}")

(defvar *fs-source*
  "#version 330 core
out vec4 FragColor;

void main()
{
    FragColor = vec4(0.0f, 0.5f, 0.2f, 1.0f);
}")

(defun to-gl-array (seq type &aux (length (length seq))
                                  (arr (gl:alloc-gl-array type length)))
  (dotimes (i length)
    (setf (gl:glaref arr i) (aref seq i)))
  arr)


(defun render (program)
  (let* ((buffers (gl:gen-buffers 2))
         (vertex-buffer (elt buffers 0))
         (arr (to-gl-array #(1.0 1.0 -1.0 -1.0 1.0 -1.0) :float))
         (c2d (gl:get-attrib-location program "c2d")))
    (gl:clear :color-buffer)
    (gl:bind-buffer :array-buffer vertex-buffer)
    (gl:buffer-data :array-buffer :static-draw arr)

    (gl:vertex-attrib-pointer c2d 2 :float nil 0 (cffi:null-pointer))
    (gl:enable-vertex-attrib-array c2d)
    (gl:use-program program)

    (gl:draw-arrays :triangles 0 3)
    (gl:free-gl-array arr)

    (gl:disable-vertex-attrib-array c2d)
    (gl:flush)))


(defun make-program ()
  (let ((vs (gl:create-shader :vertex-shader))
        (fs (gl:create-shader :fragment-shader))
        (program (gl:create-program)))

    (gl:shader-source vs *vs-source*)
    (gl:compile-shader vs)
    (gl:shader-source fs *fs-source*)
    (gl:compile-shader fs)
    (debug-log "compile vs: ~D~%" (gl:get-shader-info-log vs))
    (debug-log "compile fs: ~D~%" (gl:get-shader-info-log fs))
    (gl:attach-shader program vs)
    (gl:attach-shader program fs)
    (gl:link-program program)
    (debug-log "link: ~D~%" (gl:get-program-info-log program))
    program))

(defun gl-init ()
  (gl:viewport 0 0 800 600)
  (gl:load-identity)
  (gl:clear-color 1.0 0.5 0.5 1.0))


(defun main ()
  "The entry point of our game."
  (sdl2:with-init (:everything)
    (volume-utils:debug-log "Using SDL library version: ~D.~D.~D~%"
      sdl2-ffi:+sdl-major-version+
      sdl2-ffi:+sdl-minor-version+
      sdl2-ffi:+sdl-patchlevel+)
    (sdl2:with-window (win :flags '(:shown :opengl )) ; :resizable
      (sdl2:with-gl-context (gl-context win)
        (debug-log "Setting up window/gl.~%")
        (sdl2:gl-make-current win gl-context)
        (gl-init)
        (let ((program (make-program)))
          (sdl2:with-event-loop (:method :poll)
            (:idle ()
              (render program)
              (sdl2:gl-swap-window win))
            (:quit () t)))))))

(main)