examples: Add gameloop example

Signed-off-by: Lilis Iskandar <lilis@veand.co>

examples/gameloop/pollevent.go

@@ -0,0 +1,101 @@
+package main
+
+import "github.com/veandco/go-sdl2/sdl"
+
+const (
+	TITLE     = "README"
+	WIDTH     = 800
+	HEIGHT    = 600
+	FRAMERATE = 60
+)
+
+var (
+	playerX, playerY   = int32(WIDTH / 2), int32(HEIGHT / 2)
+	playerVX, playerVY = int32(0), int32(0)
+	running            = true
+)
+
+func main() {
+	if err := sdl.Init(sdl.INIT_EVERYTHING); err != nil {
+		panic(err)
+	}
+	defer sdl.Quit()
+
+	window, err := sdl.CreateWindow(TITLE, sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, sdl.WINDOW_SHOWN)
+	if err != nil {
+		panic(err)
+	}
+	defer window.Destroy()
+
+	surface, err := window.GetSurface()
+	if err != nil {
+		panic(err)
+	}
+
+	for running {
+		for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
+			handleEvent(event)
+		}
+
+		loopTime := loop(surface)
+		window.UpdateSurface()
+
+		delay := (1000 / FRAMERATE) - loopTime
+		sdl.Delay(delay)
+	}
+}
+
+func handleEvent(event sdl.Event) {
+	switch t := event.(type) {
+	case sdl.QuitEvent: // NOTE: Please use `*sdl.QuitEvent` for `v0.4.x` (current version).
+		println("Quitting..")
+		running = false
+		break
+	case sdl.KeyboardEvent:
+		if t.State == sdl.RELEASED {
+			if t.Keysym.Sym == sdl.K_LEFT {
+				playerVX -= 1
+			} else if t.Keysym.Sym == sdl.K_RIGHT {
+				playerVX += 1
+			}
+			if t.Keysym.Sym == sdl.K_UP {
+				playerVY -= 1
+			} else if t.Keysym.Sym == sdl.K_DOWN {
+				playerVY += 1
+			}
+		}
+		break
+	}
+}
+
+func loop(surface *sdl.Surface) (loopTime uint32) {
+	// Get time at the start of the function
+	startTime := sdl.GetTicks()
+
+	// Update player position
+	playerX += playerVX
+	playerY += playerVY
+	if playerX < 0 {
+		playerX = WIDTH
+	} else if playerX > WIDTH {
+		playerX = 0
+	}
+	if playerY < 0 {
+		playerY = HEIGHT
+	} else if playerY > HEIGHT {
+		playerY = 0
+	}
+
+	// Clear surface
+	surface.FillRect(nil, 0)
+
+	// Draw on the surface
+	rect := sdl.Rect{playerX, playerY, 4, 4}
+	colour := sdl.Color{R: 255, G: 0, B: 255, A: 255} // purple
+	pixel := sdl.MapRGBA(surface.Format, colour.R, colour.G, colour.B, colour.A)
+	surface.FillRect(&rect, pixel)
+
+	// Calculate time passed since start of the function
+	endTime := sdl.GetTicks()
+	return endTime - startTime
+}

examples/gameloop/waitevent.go

@@ -0,0 +1,82 @@
+package main
+
+import "github.com/veandco/go-sdl2/sdl"
+
+const (
+	TITLE  = "README"
+	WIDTH  = 800
+	HEIGHT = 600
+)
+
+var (
+	playerX, playerY = int32(WIDTH / 2), int32(HEIGHT / 2)
+	running          = true
+)
+
+func main() {
+	if err := sdl.Init(sdl.INIT_EVERYTHING); err != nil {
+		panic(err)
+	}
+	defer sdl.Quit()
+
+	window, err := sdl.CreateWindow(TITLE, sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, sdl.WINDOW_SHOWN)
+	if err != nil {
+		panic(err)
+	}
+	defer window.Destroy()
+
+	surface, err := window.GetSurface()
+	if err != nil {
+		panic(err)
+	}
+
+	// Draw initial frame
+	draw(window, surface)
+
+	// Event loop
+	for event := sdl.WaitEvent(); event != nil; event = sdl.WaitEvent() {
+		switch t := event.(type) {
+		case sdl.QuitEvent: // NOTE: Please use `*sdl.QuitEvent` for `v0.4.x` (current version).
+			println("Quitting..")
+			return
+		case sdl.KeyboardEvent:
+			if t.State == sdl.RELEASED {
+				if t.Keysym.Sym == sdl.K_LEFT {
+					playerX -= 4
+				} else if t.Keysym.Sym == sdl.K_RIGHT {
+					playerX += 4
+				}
+				if t.Keysym.Sym == sdl.K_UP {
+					playerY -= 4
+				} else if t.Keysym.Sym == sdl.K_DOWN {
+					playerY += 4
+				}
+				if playerX < 0 {
+					playerX = WIDTH
+				} else if playerX > WIDTH {
+					playerX = 0
+				}
+				if playerY < 0 {
+					playerY = HEIGHT
+				} else if playerY > HEIGHT {
+					playerY = 0
+				}
+				draw(window, surface)
+			}
+			break
+		}
+	}
+}
+
+func draw(window *sdl.Window, surface *sdl.Surface) {
+	// Clear surface
+	surface.FillRect(nil, 0)
+
+	// Draw on the surface
+	rect := sdl.Rect{playerX, playerY, 4, 4}
+	colour := sdl.Color{R: 255, G: 0, B: 255, A: 255} // purple
+	pixel := sdl.MapRGBA(surface.Format, colour.R, colour.G, colour.B, colour.A)
+	surface.FillRect(&rect, pixel)
+
+	window.UpdateSurface()
+}