速度

Velocity (not to be confused with gravity) is defined as speed in a given direction, and can, therefore, be negative, unlike speed alone (which is directionless and always positive). It is often used in projects for physics effects. Using velocity is a far smoother and aesthetically pleasing method than traditional scrolling.

How to Program Velocity in Scratch

A common method used to program velocity is by maintaining its value as a variable and using that to change the sprite’s position:

 when green flag clicked forever if <key [left arrow v] pressed?> then change [Velocity v] by (-1) //reduce velocity for accelerating towards the left end if <key [right arrow v] pressed?> then change [Velocity v] by (1) //increase velocity for accelerating towards the right end set [Velocity v] to ((Velocity) * (0.9)) //gradually lose speed (regardless of direction) change x by (Velocity) //change the sprite's position based on the updated velocity 

The above technique is simple, efficient and contained within a single script. The numbers can be changed to affect how quickly the sprite can change its velocity. It should be noted that the number in the last set variable block must be between 0 and 1, or the sprite will speed up rather than slowing down gradually.

示例用途

Velocity has many uses — it can be used almost anywhere. A few of the many uses are below:

  • Racing and driving games — Vehicles with velocity are more realistic to drive with.
  • Platformers — Velocity makes the movement more realistic.
  • Physics simulations — For example, a bouncing ball can use this.
  • Scrolling projects — Scrollers with velocity are popular[citation needed].
  • Fidget Spinners — Fidget Spinners run much more smoothly with velocity.
  • Space games — Space games such as “Asteroids” look more realistic using velocity.

In general, anywhere that a sprite is moving — simple on-off movement — can easily be enhanced with velocity.

示例项目

Below are some projects that use velocity:

参见

  • Finding Direction with Velocity
  • Physics
  • Physics Engine
  • Simulating Gravity

外部链接