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18-project-bouncing-ball/README.md

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+# 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.
+
+## 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.
+
+* **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)
+
+## 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
+
+* 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.
+
+* 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
+
+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.
+
+  * **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.
+
+```go
+// TIP for converting the buffer
+var buffer []rune
+
+// For printing, you can convert a rune slice to a string like so:
+str := string(buffer)
+```
+
+## 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 :)
+
+```go
+time.Sleep(time.Second / 20)
+```