The is a demonstration of two basic principles, but is basically a series of buffers designed to reduce the amount of work that the paintComponent does…
Generally speaking, it is faster to BLIT a image onto the graphics card then it is to “paint” pixels, with this in mind, this example does two things…
Firstly, it pre-renders the background map. This example just randomly generates the map when it’s run, but creates a map which is about 4 times that of full HD.
Secondly, it employees it’s own double buffering. The “view” has two buffers, an active and an update. The active buffer is what gets painted to the screen, the update buffer is what’s used by the Engine to render the current state of the output…
This is important, because the view’s buffers are ALWAYS the same size of the view, so you are never rendering anything that doesn’t appear off the screen.
This example pushes the rendering of additional content (like animation, special effects) to the Engine…
I had this example running on my 30″ monitor at 2560×1600 with very little issues, the movement delta is very small so I can pan faster, making it large would have nullified these issues…
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.HashSet;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.locks.ReentrantLock;
import javax.imageio.ImageIO;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class TestRender {
public static void main(String[] args) {
new TestRender();
}
public TestRender() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public interface View {
public BufferedImage switchBuffers();
public int getWidth();
public int getHeight();
}
public enum KeyState {
UP, DOWN, LEFT, RIGHT;
}
public class TestPane extends JPanel implements View {
private Engine engine;
private BufferedImage active;
private BufferedImage update;
private ReentrantLock lckBuffer;
public TestPane() {
lckBuffer = new ReentrantLock();
initBuffers();
engine = new Engine(this);
engine.gameStart();
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, false), "up_pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, false), "down_pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "left_pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "right_pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "up_released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "down_released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "left_released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "right_released");
ActionMap am = getActionMap();
am.put("up_pressed", new AddState(engine, KeyState.UP));
am.put("up_released", new RemoveState(engine, KeyState.UP));
am.put("down_pressed", new AddState(engine, KeyState.DOWN));
am.put("down_released", new RemoveState(engine, KeyState.DOWN));
am.put("left_pressed", new AddState(engine, KeyState.LEFT));
am.put("left_released", new RemoveState(engine, KeyState.LEFT));
am.put("right_pressed", new AddState(engine, KeyState.RIGHT));
am.put("right_released", new RemoveState(engine, KeyState.RIGHT));
}
protected void initBuffers() {
if (getWidth() > 0 && getHeight() > 0) {
try {
lckBuffer.lock();
active = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
update = new BufferedImage(getWidth(), getHeight(), BufferedImage.TYPE_INT_ARGB);
} finally {
lckBuffer.unlock();
}
}
}
@Override
public void invalidate() {
super.invalidate();
initBuffers();
}
@Override
public Dimension getPreferredSize() {
return new Dimension(1920, 1080);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
try {
lckBuffer.lock();
if (active != null) {
g2d.drawImage(active, 0, 0, this);
}
} finally {
lckBuffer.unlock();
}
g2d.dispose();
}
@Override
public BufferedImage switchBuffers() {
try {
lckBuffer.lock();
BufferedImage tmp = active;
active = update;
update = tmp;
repaint();
} finally {
lckBuffer.unlock();
}
return update;
}
}
public static class Engine {
public static final int MAP_WIDTH = 15 * 4;
public static final int MAP_HEIGHT = 9 * 4;
public static final int X_DELTA = 32;
public static final int Y_DELTA = 32;
//This value would probably be stored elsewhere.
public static final double GAME_HERTZ = 60.0;
//Calculate how many ns each frame should take for our target game hertz.
public static final double TIME_BETWEEN_UPDATES = 1000000000 / GAME_HERTZ;
//We will need the last update time.
static double lastUpdateTime = System.nanoTime();
//Store the last time we rendered.
static double lastRenderTime = System.nanoTime();
//If we are able to get as high as this FPS, don't render again.
final static double TARGET_FPS = GAME_HERTZ;
final static double TARGET_TIME_BETWEEN_RENDERS = 1000000000 / TARGET_FPS;
//Simple way of finding FPS.
static int lastSecondTime = (int) (lastUpdateTime / 1000000000);
public static int fps = 60;
public static int frameCount = 0;
private boolean isGameFinished;
private BufferedImage map;
private BufferedImage tiles[];
private View view;
private int camX, camY;
private Set<KeyState> keyStates;
public Engine(View bufferRenderer) {
keyStates = new HashSet<>(4);
this.view = bufferRenderer;
tiles = new BufferedImage[7];
Random rnd = new Random();
map = new BufferedImage(MAP_WIDTH * 128, MAP_HEIGHT * 128, BufferedImage.TYPE_INT_ARGB);
Graphics2D g2d = map.createGraphics();
for (int row = 0; row < MAP_HEIGHT; row++) {
for (int col = 0; col < MAP_WIDTH; col++) {
int tile = rnd.nextInt(7);
int x = col * 128;
int y = row * 128;
g2d.drawImage(getTile(tile), x, y, null);
}
}
g2d.dispose();
}
protected BufferedImage getTile(int tile) {
BufferedImage img = tiles[tile];
if (img == null) {
try {
img = ImageIO.read(getClass().getResource("https://stackoverflow.com/" + tile + ".png"));
img = img.getSubimage(0, 64, 128, 128);
} catch (IOException ex) {
ex.printStackTrace();
}
tiles[tile] = img;
}
return img;
}
public void gameStart() {
Thread gameThread = new Thread() {
// Override run() to provide the running behavior of this thread.
@Override
public void run() {
gameLoop();
}
};
gameThread.setDaemon(false);
// Start the thread. start() calls run(), which in turn calls gameLoop().
gameThread.start();
}
public void gameLoop() {
BufferedImage buffer = view.switchBuffers(); // initial buffer...
while (!isGameFinished) {
double now = System.nanoTime();
lastUpdateTime += TIME_BETWEEN_UPDATES;
gameUpdate(buffer);
renderBuffer(buffer);
buffer = view.switchBuffers(); // Push the buffer back
frameCount++;
lastRenderTime = now;
int thisSecond = (int) (lastUpdateTime / 1000000000);
if (thisSecond > lastSecondTime) {
fps = frameCount;
frameCount = 0;
lastSecondTime = thisSecond;
}
//Yield until it has been at least the target time between renders. This saves the CPU from hogging.
while (now - lastRenderTime < TARGET_TIME_BETWEEN_RENDERS && now - lastUpdateTime < TIME_BETWEEN_UPDATES) {
//Thread.yield();
//This stops the app from consuming all your CPU. It makes this slightly less accurate, but is worth it.
//You can remove this line and it will still work (better), your CPU just climbs on certain OSes.
//FYI on some OS's this can cause pretty bad stuttering. Scroll down and have a look at different peoples' solutions to this.
try {
Thread.sleep(1);
} catch (Exception e) {
}
now = System.nanoTime();
}
}
}
protected void renderBuffer(BufferedImage buffer) {
if (buffer != null) {
Graphics2D g2d = buffer.createGraphics();
g2d.drawImage(map, camX, camY, null);
g2d.dispose();
}
}
protected void gameUpdate(BufferedImage buffer) {
// render transient effects here
if (keyStates.contains(KeyState.DOWN)) {
camY -= Y_DELTA;
} else if (keyStates.contains(KeyState.UP)) {
camY += Y_DELTA;
}
if (camY < -(map.getHeight() - view.getHeight())) {
camY = -(map.getHeight() - view.getHeight());
} else if (camY > 0) {
camY = 0;
}
if (keyStates.contains(KeyState.RIGHT)) {
camX -= Y_DELTA;
} else if (keyStates.contains(KeyState.LEFT)) {
camX += Y_DELTA;
}
if (camX < -(map.getWidth() - view.getWidth())) {
camX = -(map.getWidth() - view.getWidth());
} else if (camX > 0) {
camX = 0;
}
}
public void addKeyState(KeyState state) {
keyStates.add(state);
}
public void removeKeyState(KeyState state) {
keyStates.remove(state);
}
}
public class AddState extends AbstractAction {
private Engine engine;
private KeyState state;
public AddState(Engine engine, KeyState state) {
this.engine = engine;
this.state = state;
}
@Override
public void actionPerformed(ActionEvent e) {
engine.addKeyState(state);
}
}
public class RemoveState extends AbstractAction {
private Engine engine;
private KeyState state;
public RemoveState(Engine engine, KeyState state) {
this.engine = engine;
this.state = state;
}
@Override
public void actionPerformed(ActionEvent e) {
engine.removeKeyState(state);
}
}
}
During my experimentation, I did notice that, if you tried to render the content “beyond” the range of the buffer (ie allow the top of the map to slip down inside the buffer area), you would get nasty paint effects, so beware that you are always rendering within the viewable area of the buffer…
There are probably other areas that need tidying up, but this demonstrates the basics…