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add: bouncing ball exercise #2

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Inanc Gumus
2019-03-14 21:16:15 +03:00
parent 3271dd5e63
commit cc32a31c1b
5 changed files with 249 additions and 27 deletions
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40
18-bouncing-ball-project/README.md
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@ -2,13 +2,11 @@
Use the following tips only when you get stuck. This document isn't in a particular order, please do not follow it like so.
➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖
## Ball position and velocity
## CALCULATING THE 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.
* On each loop step: Add velocities to ball's position. This will make the ball move.
* **Velocity means: Speed and Direction**
@ -18,36 +16,26 @@ On each loop step: Add velocities to ball's position. This will make the ball mo
* 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
* [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)
## CREATE THE BOARD
## CREATING 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.
➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖
## CLEARING THE SCREEN
## CLEAR THE SCREEN
* Before the loop, clear the screen once by using my screen package.
* Before the loop, clear the screen once by using my [screen package](https://github.com/inancgumus/screen), click on the link. You can find its [documentation here](https://godoc.org/github.com/inancgumus/screen).
* 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](https://github.com/inancgumus/screen).
* Its documentation is [here](https://godoc.org/github.com/inancgumus/screen).
* You can find more information about it in the Retro Clock project section.
* You can find more information about the screen package and screen clearing in the [Retro Clock project section lectures](https://github.com/inancgumus/learngo/tree/master/15-project-retro-led-clock).
➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖
## DRAWING THE BOARD
## 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.
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` slice as a buffer because `rune` can store an emoji character.
* Make a large enough rune slice named `buf` using the `make` function.
@ -65,10 +53,10 @@ var buffer []rune
str := string(buffer)
```
➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖
## SLOW DOWN THE SPEED
## SLOWING 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)`
```go
time.Sleep(time.Second / 20)
```

5
18-bouncing-ball-project/exercises/01-width-and-height/main.go
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@ -20,6 +20,9 @@
//
// 1. Go here: https://godoc.org/golang.org/x/crypto/ssh/terminal
//
// Download the package:
// go get -u golang.org/x/crypto/ssh/terminal
//
// 2. Find the function that gives you the width and height
// of the terminal.
//
@ -47,7 +50,7 @@
// columns (or cells). Ordinary characters have a
// single column.
//
// 1. Get the width of the ball emoji using function
// 1. Get the width of the ball emoji using a function
// from the following package:
//
// go get -u github.com/mattn/go-runewidth

126
18-bouncing-ball-project/exercises/02-previous-positions/main.go Normal file
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@ -0,0 +1,126 @@
// For more tutorials: https://blog.learngoprogramming.com
//
// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
package main
import (
"fmt"
"time"
"github.com/inancgumus/screen"
"github.com/mattn/go-runewidth"
)
// ---------------------------------------------------------
// EXERCISE: Previous positions
//
// Let's optimize the program once more. This time you're
// going to optimize the clearing off the previous positions.
//
// 1. Find the code below marked as "remove the previous ball"
//
// 2. Instead of clearing every position on the board to false,
// only set the previous position to false. So, don't use
// a loop, remove it.
//
// 3. Change the velocity of the ball like so:
//
// vx, vy = 5, 2
//
// 4. Run the program and solve the problem
//
//
// HINT
//
// Don't forget saving the previous position.
//
// ---------------------------------------------------------
func main() {
const (
cellEmpty = ' '
cellBall = '⚾'
maxFrames = 1200
speed = time.Second / 20
)
var (
px, py int // ball position
vx, vy = 1, 1 // velocities
cell rune // current cell (for caching)
)
// you can get the width and height using the screen package easily:
width, height := screen.Size()
// get the rune width of the ball emoji
ballWidth := runewidth.RuneWidth(cellBall)
// adjust the width and height
width /= ballWidth
height-- // there is a 1 pixel border in my terminal
// create the board
board := make([][]bool, width)
for row := range board {
board[row] = make([]bool, height)
}
// create a drawing buffer
buf := make([]rune, 0, width*height)
// clear the screen once
screen.Clear()
for i := 0; i < maxFrames; i++ {
// calculate the next ball position
px += vx
py += vy
// when the ball hits a border reverse its direction
if px <= 0 || px >= width-1 {
vx *= -1
}
if py <= 0 || py >= height-1 {
vy *= -1
}
// remove the previous ball
for y := range board[0] {
for x := range board {
board[x][y] = false
}
}
// put the new ball
board[px][py] = true
// rewind the buffer (allow appending from the beginning)
buf = buf[:0]
// draw the board into the buffer
for y := range board[0] {
for x := range board {
cell = cellEmpty
if board[x][y] {
cell = cellBall
}
buf = append(buf, cell, ' ')
}
buf = append(buf, '\n')
}
// print the buffer
screen.MoveTopLeft()
fmt.Print(string(buf))
// slow down the animation
time.Sleep(speed)
}
}

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18-bouncing-ball-project/exercises/02-previous-positions/solution/main.go Normal file
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@ -0,0 +1,101 @@
// For more tutorials: https://blog.learngoprogramming.com
//
// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
package main
import (
"fmt"
"time"
"github.com/inancgumus/screen"
"github.com/mattn/go-runewidth"
)
func main() {
const (
cellEmpty = ' '
cellBall = '⚾'
maxFrames = 1200
speed = time.Second / 20
)
var (
px, py int // ball position
ppx, ppy int // previous ball position
vx, vy = 5, 2 // velocities
cell rune // current cell (for caching)
)
// you can get the width and height using the screen package easily:
width, height := screen.Size()
// get the rune width of the ball emoji
ballWidth := runewidth.RuneWidth(cellBall)
// adjust the width and height
width /= ballWidth
height-- // there is a 1 pixel border in my terminal
// create the board
board := make([][]bool, width)
for row := range board {
board[row] = make([]bool, height)
}
// create a drawing buffer
buf := make([]rune, 0, width*height)
// clear the screen once
screen.Clear()
for i := 0; i < maxFrames; i++ {
// calculate the next ball position
px += vx
py += vy
// when the ball hits a border reverse its direction
if px <= 0 || px >= width-1 {
vx *= -1
}
if py <= 0 || py >= height-1 {
vy *= -1
}
// check whether the ball goes beyond the borders
if px < width && py < height {
// remove the previous ball and put the new ball
board[px][py], board[ppx][ppy] = true, false
// save the previous positions
ppx, ppy = px, py
}
// rewind the buffer (allow appending from the beginning)
buf = buf[:0]
// draw the board into the buffer
for y := range board[0] {
for x := range board {
cell = cellEmpty
if board[x][y] {
cell = cellBall
}
buf = append(buf, cell, ' ')
}
buf = append(buf, '\n')
}
// print the buffer
screen.MoveTopLeft()
fmt.Print(string(buf))
// slow down the animation
time.Sleep(speed)
}
}

4
18-bouncing-ball-project/exercises/README.md
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@ -4,3 +4,7 @@
In this exercise, your goal is getting the width and height of the terminal screen from your operating system (instead of setting the width and height manually).
2. **[Previous positions](https://github.com/inancgumus/learngo/tree/master/18-bouncing-ball-project/exercises/02-previous-positions)**
Let's optimize the program once more. This time you're going to optimize the clearing off the previous positions.