rename: bouncing ball

18-project-bouncing-ball/03-animate/main.go

@@ -0,0 +1,93 @@
+// 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"
+)
+
+func main() {
+	const (
+		width  = 50
+		height = 10
+
+		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)
+	)
+
+	// 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)
+	}
+}