learngo/x-tba/slices/21-bouncing-ball-project

Bouncing Ball Challenge Tips

Use the following tips only when you get stuck. This document isn't in a particular order, please do not follow it like so.

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Ball position and velocity

You can use velocity to change the ball's speed and position. In my example, the speed is constant, so I always use unit value: 1.

On each loop step: Add velocities to ball's position. This will make the ball move.

• Velocity means: Speed and Direction

  • X velocity = 1 -> ball moves right
  • X velocity = -1 -> ball moves left
  • Y velocity = 1 -> ball moves down
  • Y velocity = -1 -> ball moves up

• For more information on graphics and velocity:

  • Youtube: Crash Course: 2D Graphics -> https://www.youtube.com/watch?v=7Jr0SFMQ4Rs&t=529

  • Youtube: Crash Course: Velocity -> https://www.youtube.com/watch?v=ZM8ECpBuQYE

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CREATE THE BOARD

I use [][]bool for the board but you can use anything you like. For example, you can directly use [][]rune or []rune. Experiment with them and decide which one is the best for you.

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CLEAR THE SCREEN

• Before the loop, clear the screen once by using my screen package.

• After each loop step, move the cursor to the top-left position by using the screen package. So that you can draw the animation frame all over again in the same position.

• It's here.

• Its documentation is here.

• You can find more information about it in the Retro Clock project section.

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DRAW THE BOARD

Instead of drawing the board and the ball to the screen everytime, you will fill a buffer, and when you complete, you can draw the board and the ball once by printing the buffer.

I use a []rune buffer because rune can store an emoji character, and I use a slice of runes because I want to draw empty cells and a ball in the end.

• Make a large enough rune slice named buf using the make function.

  • HINT: width * height will give you a large enough buffer.

  • TIP: You could also use string concatenation to draw into a string buffer but it would be inefficient.

  • You will find more information about bytes and runes in the strings section.

// TIP for converting the buffer
var buffer []rune

// For printing, you can convert a rune slice to a string like so:
str := string(buffer)

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SLOW DOWN THE SPEED

Call the time.Sleep function to slow down the speed of the loop a little bit, so you can see the ball :)

time.Sleep(time.Second / 20)