implementing a simple game using libgdx

libGDX: Implemen.ng a Simple Game

Jussi Pohjolainen Tampere University of Applied Sciences

Starter Class: Desktop public class Main {

public static void main(String[] args) {

LwjglApplicationConfiguration config = new LwjglApplicationConfiguration();

config.title = "Gorba's Revenge";

config.width = 800;

config.height = 480;

new LwjglApplication(new MyGame(), config);

}

}

// In Android, the resolution is set by operating system!

public class MyGame implements ApplicationListener { // Method called once when the application is created. public void create () { } // Method called by the game loop from the application // every time rendering should be performed. Game logic // updates are usually also performed in this method. public void render () { } // This method is called every time the game screen is re-sized // and the game is not in the paused state. It is also called once // just after the create() method. // The parameters are the new width and height the screen has been resized to in pixels. public void resize (int width, int height) { } // On Android this method is called when the Home button is // pressed or an incoming call is received. On desktop this is called // just before dispose() when exiting the application. // A good place to save the game state. public void pause () { } // This method is only called on Android, when the application // resumes from a paused state. public void resume () { } // Called when the application is destroyed. It is preceded by a call to pause(). public void dispose () { } }

Assets

•  Drag sounds, images to android/assets folder –  Desktop app has a link to that folder

Asset loading

public class MyGame implements ApplicationListener {

private Texture gorbaImage;

private Sound soundEffect;

private Music backgroundMusic;

@Override

public void create() {

// gorba.png uploaded to GPU and is ready to be used by OpenGL. Image format

// must be .jpg, .png, .bmp

gorbaImage = new Texture(Gdx.files.internal(”gorba.png"));

// Stored in RAM

soundEffect = Gdx.audio.newSound(Gdx.files.internal("beep.wav"));

// Streamed from wherever it’s stored

backgroundMusic = Gdx.audio.newMusic(Gdx.files.internal("ussranthem.mp3"));

// start the playback of the background music immediately

rainMusic.setLooping(true);

rainMusic.play();

}

public void dispose() {

// Good practice to dispose (clean) assets

gorbaImage.dispose();

soundEffect.dispose();

backgroundMusic.dispose();

}

Rendering: Camera

•  Camera is like “virtual window into our world” – What part of the “world” is visible?

•  Camera – OrthographicCamera • When the human eye looks at a scene, objects in the distance appear smaller than objects close by. Orthographic projec.on ignores this effect

– PerspectiveCamera •  Closer objects appear bigger in Perspec.veCamera

Using Camera public class SimpleGame extends ApplicationAdapter {

private OrthographicCamera camera;

@Override


camera = new OrthographicCamera();

// Sets this camera to an orthographic projection,

// centered at (viewportWidth/2, viewportHeight/2),

// with the y-axis pointing up or down.

// true => y points down, false => y points up

camera.setToOrtho(false, 800, 480);

Word about OpenGL

•  OpenGL (Open Graphics Library) is a cross-‐language, mul.-‐plaRorm applica.on programming interface (API) for rendering 2D and 3D vector graphics.

•  The API is typically used to interact with a graphics processing unit (GPU), to achieve hardware-‐accelerated rendering.

•  Widely used in CAD, virtual reality, scien.fic visualiza.on, informa.on visualiza.on, flight simula.on, and video games.

•  libGDX uses OpenGL ES and has interface also for direct access for OpenGL

Texture Mapping

•  A Texture wraps a standard OpenGL ES texture. –  A texture is an OpenGL Object that contains one or more images that all have the same image format.

•  Image loaded into the GPU’s memory in raw format •  Texture mapping is process of working out where in space the texture will be applied –  “To s.ck a poster on a wall, one needs to figure out where on the wall he will be gluing the corners of the paper”

–  Space ó Wall – Mesh (Rectangle) ó Paper –  Image on paper ó Texture

SpriteBatch

•  SpriteBatch class takes care of texture mapping

•  Convenience class which makes drawing onto the screen easy

public class SimpleGame extends ApplicationAdapter {


private OrthographicCamera camera;

private SpriteBatch batch;

@Override


camera = new OrthographicCamera();

batch = new SpriteBatch();

// Sets this camera to an orthographic projection, centered at (viewportWidth/2, viewportHeight/2),

// with the y-axis pointing up or down. true => y points down, false => y points up

camera.setToOrtho(false, 800, 480);

gorbaImage = new Texture(Gdx.files.internal("littlegorba.png"));

}

@Override

public void render() {

// Let's use the coordinate system specified by the camera

batch.setProjectionMatrix(camera.combined);

// SpriteBatch is ready for commands

batch.begin();

// Draw a texture to x = 100, y = 100

batch.draw(gorbaImage, 100, 100);




// No commands anymore, proceed to process the batch of commands

// received

batch.end();

}

}

Clear Screen @Override public void render() { // Direct OpenGL call // float red [0,1] // green // blue // alpha // https://www.opengl.org/sdk/docs/man/html/glClearColor.xhtml Gdx.gl.glClearColor(0, 0, 0.2f, 1); // Clear the screen with the color chosen // http://www.opengl.org/sdk/docs/man/html/glClear.xhtml Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT); // SpriteBatch is ready for commands batch.begin(); // Draw a texture to x = 100, y = 100 batch.draw(gorbaImage, 100, 100); batch.draw(gorbaImage, 140, 100); batch.draw(gorbaImage, 180, 100); batch.draw(gorbaImage, 220, 100); // No commands anymore, proceed to process the batch of commands // received batch.end(); }

Gdx.input

•  Ge]ng input from user is very easy •  Touch – Gdx.input.isTouched() – Gdx.input.getX() – Gdx.input.getY()

•  Accelerometer – Gdx.input.getAccelerometerX() – Gdx.input.getAccelerometerY() – Gdx.input.getAccelerometerZ()

About Resolu.on

•  Game can be cross-‐plaRorm, what is the resolu.on?

•  We have two resolu.ons – The real resolu.on – The world resolu.on

•  Mapping must be done between these two!

Real resolu.on 0,0 World resolu.on 0,480


Window resolu.on 800 x 480 World resolu.on set to 800 x 480



Window width 640 x 384 World resolu.on set to 800 x 480

Conversion @Override public void render() { if(Gdx.input.isTouched()) { int realX = Gdx.input.getX(); int realY = Gdx.input.getY(); // Encapsulated 3D Vector, only 2D is used // Vectors can be used for represent a direction and position

// Bad practice to instantiate every render – call! Vector3 touchPos = new Vector3(realX, realY, 0); // Function to translate a point given in screen coordinates to world space. camera.unproject(touchPos); Gdx.app.setLogLevel(Logger.DEBUG); Gdx.app.debug("MyGame", "real X = " + realX); Gdx.app.debug("MyGame", "real Y = " + realY); Gdx.app.debug("MyGame", "world X = " + touchPos.x); Gdx.app.debug("MyGame", "world Y = " + touchPos.y); } }

Collision

•  Simple collision detec.on is done using overlaps method of Rectangle

•  Remember Texture Mapping? – Texture (image) – Mesh (rectangle)

•  Create rectangle for each texture •  if(rect1.overlaps(rect2)) { .. }

public class SimpleGame extends ApplicationAdapter {


private Rectangle gorbaRectangle;

private Texture phoneImage;

private Rectangle phoneRectangle;

@Override


gorbaImage = new Texture(Gdx.files.internal("littlegorba.png"));

phoneImage = new Texture(Gdx.files.internal("phone.png"));

// new Rectangle (x, y, width, height)

gorbaRectangle = new Rectangle(200,200,24,33);

phoneRectangle = new Rectangle(300,300,17,45);

}

@Override

public void render() {

batch.begin();

batch.draw(gorbaImage, gorbaRectangle.x, gorbaRectangle.y);

batch.draw(phoneImage, phoneRectangle.x, phoneRectangle.x);

batch.end();

if(Gdx.input.isTouched()) {

int realX = Gdx.input.getX();

int realY = Gdx.input.getY();

Vector3 touchPos = new Vector3(realX, realY, 0);

camera.unproject(touchPos);

gorbaRectangle.x = touchPos.x;

gorbaRectangle.y = touchPos.y;

}

if(gorbaRectangle.overlaps(phoneRectangle)) {

Gdx.app.debug("MyGame", "Crash!");

}

}

}

Texture + Rectangle

•  Texture (image) and Rectangle (“paper”) go hand in hand

•  It would be great to map these into one class, for example Sprite – Don’t implement one, libgdx has Sprite J

•  hfp://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/graphics/g2d/Sprite.html

Sprite usage Sprite gorbaSprite = new Sprite(new Texture(Gdx.files.internal("littlegorba.png")),

24,

33);

// Rendering using SpriteBatch

gorbaSprite.draw(batch);

// Collision

if( gorbaSprite.getBoundingRectangle()

.overlaps(phoneSprite.getBoundingRectangle()) ) {

// Crash

}

implementing a simple game using libgdx

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