nature-of-code/01. Vectors/Example 1.4 - Multiplying a vector/sketch.lisp at master · mark-gerarts/nature-of-code · GitHub

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(defpackage :nature-of-code.vectors.example-4
  (:export :start-sketch)
  (:use :cl :trivial-gamekit))
(in-package :nature-of-code.vectors.example-4)

(defvar *width* 800)
(defvar *height* 600)

(defvar *black* (vec4 0 0 0 1))

(defgame sketch ()
  ((center
    :initform (vec2 (/ *width* 2) (/ *height* 2))
    :accessor center)
   (mouse-position
    :initform (vec2 0 0)
    :accessor mouse-position))
  (:viewport-width *width*)
  (:viewport-height *height*)
  (:viewport-title "Multiplying a vector"))

(defmethod post-initialize ((this sketch))
  (bind-cursor (lambda (x y)
                 (setf (mouse-position this) (vec2 x y)))))

(defmethod draw ((this sketch))
  (let* ((center (center this))
         (sub (subt (mouse-position this) center)))
    (translate-canvas (x center) (y center))
    (setf sub (mult sub 0.5))
    (draw-line (vec2 0 0) sub *black* :thickness 2)))

(defun start-sketch ()
  (start 'sketch))