Zho:物理引擎

物理引擎(physics engine)is a 编程方法 used for creating the physics, or movement, in a 专案. This movement can include jumping, side-motion, wall-jumping, and more. Physics engines are commonly designed once and used for many projects or borrowed by other Scratch 用户s to save the time of recreating one. This article contains an example physics engine which can be used in a Scratch project.

示例
This example uses only one script. It requires only one costume and contains the ability for a 角色 to: The following script would be placed into the sprite which performs the physics. 當 @greenflag 被點擊 變數 [x velocity v] 設為 (0) // 将水平（横向）的速度设定成 "0" 變數 [y velocity v] 設為 (0) // 将垂直（直向）的速度设定成 "0" 重複無限次 如果 <[向右 v] 鍵被按下？> 那麼 變數 [x velocity v] 改變 (1) // "x velocity" is the horizontal speed, and changing it by "1" makes the sprite move more right end // when you intend for the sprite to move right 如果 <[向左 v] 鍵被按下？> 那麼 變數 [x velocity v] 改變 (-1) // makes the sprite move more left end // when you intend for the sprite to move left 變數 [x velocity v] 設為 ((x velocity) * (0.9)) // for a gradual slowdown and to prevent the speed from reaching too high x 改變 (x velocity) // the actual, physical movement 如果 <碰到顏色 [#1B2BE0] ?> 那麼 y 改變 (([abs v] 數值 (x velocity)) + (1)) // the faster you move, the more velocity it has to go up a slope 如果 <碰到顏色 [#1B2BE0] ?> 那麼 y 改變 ((0) - (([abs v] 數值 (x velocity)) + (1))) // go back down it     x 改變 ((0) - (x velocity)) // go to the previous x座標 at the bottom of the slope 變數 [x velocity v] 設為 ((x velocity) / (2)) // slow down after collision with wall or steep slope end // if the slope is too steep end // if colliding with either a ramp or wall 如果 <[向上 v] 鍵被按下？> 那麼 y 改變 (-1) // truly, the sprite is 1 pixel above the platform, meaning it has to move down 1 to check if it's "on it" 如果 <碰到顏色 [#1B2BE0] ?> 那麼 變數 [y velocity v] 設為 (10) // gives the speed needed to jump end // if on the platform y 改變 (1) // go back up 1 pixel since the sprite went down 1 before to check if it was on a platform end 如果 <(y velocity) < (3)> 那麼 y 改變 (-1) // to check if on the platform 如果 <<碰到顏色 [#1B2BE0] ?> 不成立> 那麼 變數 [y velocity v] 改變 (-1) // gravity exerting a faster downward force end // if not on the platform y 改變 (1) // because before the sprite moved down 1 pixel, and now it must go back in place end // when reaching the top of a jump or falling downward 變數 [y velocity v] 設為 ((y velocity) * (.9)) // for gradual movement change, as in realistic physics y 改變 (y velocity) // the previous scripts set the speed, but now the sprite physically moves vertically 如果 <碰到顏色 [#1B2BE0] ?> 那麼 y 改變 ((0) - (y velocity)) // reverses the direction 變數 [y velocity v] 設為 ((y velocity) / (2.5)) // greatly reduces vertical speed after collision to the sprite nearly stops end // if colliding with a floor or ceiling end There is a bug where after you jump, if there is a wall too close to the sprite, then there is some velocity "left over" and the sprite jumps up and down quickly. It can be solved by going to the edge of the platform so the sprite goes down slightly and then moving it back up on the platform.
 * move horizontally on tilted and flat surfaces
 * jump
 * collide with a specific color (which can be modified to be a sprite)

参见

 * 跳跃
 * 让物件在卷轴上移动
 * 子弹的发射
 * 重力的模拟
 * 速度
 * 墙壁间弹跳
 * 墙壁侦测器