2D Viewport Example

package de.master.demo;

import java.awt.event.KeyEvent;

import processing.core.PApplet;
import processing.core.PImage;

public class ViewportExample extends PApplet {

    int W = KeyEvent.VK_W;
    int A = KeyEvent.VK_A;
    int S = KeyEvent.VK_S;
    int D = KeyEvent.VK_D;

    boolean[] keys;
    float speed;
    PImage background;
    PImage player;
    float tx;
    float ty;
    float sceneWidth;
    float sceneHeight;
    float playerX;
    float playerY;
    float playerScreenX;
    float playerScreenY;


    @Override
    public void setup() {
        background  = loadImage("/background.png");
        player      = loadImage("/player.png");

        sceneWidth = background.width;
        sceneHeight= background.height;

        size((int)(sceneWidth / 4.0), (int)(sceneHeight / 4.0));
        playerX = 0;
        playerY = 0;

        speed = 3;
        keys = new boolean[Short.MAX_VALUE];

        // initial setting
        tx = -(playerX - (width / 2));
        ty = -(playerY - (width / 2));

        if(tx > 0) tx = 0;
        if(ty > 0) ty = 0;

        playerScreenX = width / 2;
        playerScreenY = height / 2;

        // black
        fill(0);
        stroke(0);
    }

    @Override
    public void draw()
    {
        update();
        image(background, tx, ty);
        image(player, playerScreenX, playerScreenY);

        text((playerX + ":" + playerY), playerScreenX, playerScreenY);
        rect(playerX, playerY, 5, 5);
    }

    public void update()
    {

        if(keys[A])
        {
            playerX -= speed;

            if(playerScreenX <= width / 2 && tx < 0)
            {
                playerScreenX = width / 2;
                tx += speed;
            }
            else if(playerScreenX <= width / 2 && (tx) >= 0)
            {
                playerScreenX -= speed;
                tx = 0;

                if(playerScreenX < 0) playerScreenX = 0;
            }
            else if(playerScreenX >= width / 2 && (tx) < 0)
            {
                playerScreenX -= speed;
            }
        }
        if(keys[D])
        {
            playerX += speed;

            if(playerScreenX >= width / 2 && (-tx + width) < sceneWidth)
            {
                playerScreenX = width / 2;
                tx -= speed;
            }
            if(playerScreenX >= width / 2 && (-tx + width) >= sceneWidth)
            {
                playerScreenX += speed;
                tx = -(sceneWidth - width);
                if(playerScreenX >= width - player.width) playerScreenX = width - player.width;
            }
            if(playerScreenX <= width / 2 && (-tx + width) < sceneWidth)
            {
                playerScreenX += speed;
            }
        }
        if(keys[W])
        {
            playerY -= speed;
            if(playerScreenY <= height / 2 && ty < 0)
            {
                playerScreenY = height / 2;
                ty += speed;
            }
            else if(playerScreenY <= height / 2 && (ty) >= 0)
            {
                playerScreenY -= speed;
                ty = 0;
                if(playerScreenY < 0) playerScreenY = 0;
            }
            else if(playerScreenY >= height / 2 && (ty) < 0)
            {
                playerScreenY -= speed;
            }
        }
        if(keys[S])
        {
            playerY += speed;
            if(playerScreenY >= height / 2 && (-ty + height) < sceneHeight)
            {
                playerScreenY = height / 2;
                ty -= speed;
            }
            if(playerScreenY >= height / 2 && (-ty + height) >= sceneHeight)
            {
                playerScreenY += speed;
                ty = -(sceneHeight - height);

                if(playerScreenY >= height - player.height) playerScreenY = height - player.height;
            }
            if(playerScreenY <= height / 2 && (-ty + height) < sceneHeight)
            {
                playerScreenY += speed;
            }
        }
        if(playerX < 0) playerX = 0;
        if(playerX > sceneWidth) playerX = sceneWidth;
        if(playerY < 0) playerY = 0;
        if(playerY > sceneHeight) playerY = sceneHeight;

    }

    @Override
    public void keyPressed(KeyEvent e) {
        keys[e.getKeyCode()] = true;
    }

    @Override
    public void keyReleased(KeyEvent e) {
        keys[e.getKeyCode()] = false;
    }
}