add camera to move with w,a,s,d

main.go

@@ -6,6 +6,7 @@ import (
 	_ "image/png"
 	"math/rand"
 	"os"
+	"time"
 
 	"github.com/faiface/pixel"
 	"github.com/faiface/pixel/pixelgl"
@@ -57,17 +58,44 @@ func run() {
 		}
 	}
 
+	//camera
 	var (
+		camPos   = pixel.ZV
+		camSpeed = 500.0
 		trees    []*pixel.Sprite
 		matrices []pixel.Matrix
 	)
 
+	last := time.Now()
 	//loop until window is closed by "X" button
 	for !win.Closed() {
+		dt := time.Since(last).Seconds()
+		last = time.Now()
+
+		cam := pixel.IM.Moved(win.Bounds().Center().Sub(camPos))
+		win.SetMatrix(cam)
+
 		if win.JustPressed(pixelgl.MouseButtonLeft) {
 			tree := pixel.NewSprite(spritesheet, treesFrames[rand.Intn(len(treesFrames))])
 			trees = append(trees, tree)
-			matrices = append(matrices, pixel.IM.Scaled(pixel.ZV, 4).Moved(win.MousePosition()))
+			mouse := cam.Unproject(win.MousePosition())
+			matrices = append(matrices, pixel.IM.Scaled(pixel.ZV, 4).Moved(mouse))
+		}
+
+		if win.Pressed(pixelgl.KeyA) {
+			camPos.X -= camSpeed * dt
+		}
+
+		if win.Pressed(pixelgl.KeyD) {
+			camPos.X += camSpeed * dt
+		}
+
+		if win.Pressed(pixelgl.KeyS) {
+			camPos.Y -= camSpeed * dt
+		}
+
+		if win.Pressed(pixelgl.KeyW) {
+			camPos.Y += camSpeed * dt
 		}
 		//refresh screen and set background color
 		win.Clear(colornames.Forestgreen)