add code for 04 guide

guide/04_pressing_keys_and_clicking_mouse/main.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"image"
+	"math"
+	"math/rand"
+	"os"
+	"time"
+
+	_ "image/png"
+
+	"github.com/faiface/pixel"
+	"github.com/faiface/pixel/pixelgl"
+	"golang.org/x/image/colornames"
+)
+
+func loadPicture(path string) (pixel.Picture, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	img, _, err := image.Decode(file)
+	if err != nil {
+		return nil, err
+	}
+	return pixel.PictureDataFromImage(img), nil
+}
+
+func run() {
+	cfg := pixelgl.WindowConfig{
+		Title:  "Pixel Rocks!",
+		Bounds: pixel.R(0, 0, 1024, 768),
+		VSync:  true,
+	}
+	win, err := pixelgl.NewWindow(cfg)
+	if err != nil {
+		panic(err)
+	}
+
+	spritesheet, err := loadPicture("trees.png")
+	if err != nil {
+		panic(err)
+	}
+
+	var treesFrames []pixel.Rect
+	for x := spritesheet.Bounds().Min.X(); x < spritesheet.Bounds().Max.X(); x += 32 {
+		for y := spritesheet.Bounds().Min.Y(); y < spritesheet.Bounds().Max.Y(); y += 32 {
+			treesFrames = append(treesFrames, pixel.R(x, y, x+32, y+32))
+		}
+	}
+
+	var (
+		camPos       = pixel.V(0, 0)
+		camSpeed     = 500.0
+		camZoom      = 1.0
+		camZoomSpeed = 1.2
+		trees        []*pixel.Sprite
+	)
+
+	last := time.Now()
+	for !win.Closed() {
+		dt := time.Since(last).Seconds()
+		last = time.Now()
+
+		cam := pixel.IM.Scaled(camPos, camZoom).Moved(win.Bounds().Center() - camPos)
+		win.SetMatrix(cam)
+
+		if win.JustPressed(pixelgl.MouseButtonLeft) {
+			tree := pixel.NewSprite(spritesheet, treesFrames[rand.Intn(len(treesFrames))])
+			mouse := cam.Unproject(win.MousePosition())
+			tree.SetMatrix(pixel.IM.Scaled(0, 4).Moved(mouse))
+			trees = append(trees, tree)
+		}
+		if win.Pressed(pixelgl.KeyLeft) {
+			camPos -= pixel.X(camSpeed * dt)
+		}
+		if win.Pressed(pixelgl.KeyRight) {
+			camPos += pixel.X(camSpeed * dt)
+		}
+		if win.Pressed(pixelgl.KeyDown) {
+			camPos -= pixel.Y(camSpeed * dt)
+		}
+		if win.Pressed(pixelgl.KeyUp) {
+			camPos += pixel.Y(camSpeed * dt)
+		}
+		camZoom *= math.Pow(camZoomSpeed, win.MouseScroll().Y())
+
+		win.Clear(colornames.Forestgreen)
+
+		for _, tree := range trees {
+			tree.Draw(win)
+		}
+
+		win.Update()
+	}
+}
+
+func main() {
+	pixelgl.Run(run)
+}