Improving rendering performance of 2D Tile Game

Question

I want to see if I can make any improvements to the rendering methods that are currently written. I've noticed when profiling this project that the CPU was allocating a fair percentage of the time towards rendering and was wondering if there were any improvements that I can make towards it.

Note: Below is my somewhat simple rendering method. I am rendering an ArrayList of tiles, few of these are transparent. This function (y*map.getMapWidth())+x) will return the index in the ArrayList to be rendered.

ImageManager is a class that stores cropped images from a spritesheet as a BufferedImage.

import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
public class Game extends Canvas implements Runnable{
 private void renderTiles(Graphics g) {
 // the overlay variable determines if I need to render anything off screen
 // (True if player is moving) 
 int overlay = 0;
 if (moving) {
 overlay = 1;
 }
 // the four variables below determine the starting/finishing x/y variables 
 // to begin rendering
 int startX = -((xOffset/(Tile.TILESIZE*SCALE))+overlay);
 int finishX = -(((xOffset-(WIDTH*SCALE))/(Tile.TILESIZE*SCALE))-overlay);
 int startY = -((yOffset/(Tile.TILESIZE*SCALE))+overlay);
 int finishY = -(((yOffset-(HEIGHT*SCALE))/(Tile.TILESIZE*SCALE))-overlay);
 // to avoid crashes, the variables can't render what isn't there in the list
 if (startX < 0) {
 startX = 0; 
 } if (finishX > map.getMapWidth()) {
 finishX = map.getMapWidth(); 
 } if (startY < 0) {
 startY = 0;
 } if (finishY > map.getMapHeight()) {
 finishY = map.getMapHeight();
 } 
 // where the tiles are render. tiles are stored in an ArrayList so that 
 // switching between maps is easier
 for (int y = startY; y < finishY; y++) {
 for (int x = startX; x < finishX; x++) {
 map.tile.get((y*map.getMapWidth())+x).render(g);
 }
 }
 }
 public void render(){
 BufferStrategy bs = this.getBufferStrategy();
 if(bs == null){
 createBufferStrategy(2);
 return;
 }
 Graphics g = bs.getDrawGraphics();
 // start rendering
 g.fillRect(0, 0, WIDTH * SCALE, HEIGHT * SCALE); 
 renderTiles(g);
 player.render(g);
 g.dispose();
 bs.show();
 }
}
import java.awt.Graphics;
import java.awt.image.BufferedImage;
public abstract class Tile {
 public static final int TILESIZE = 16; 
 protected BufferedImage bi;
 protected ImageManager im;
 protected int x, y, oX, oY;
 protected Game game;
 public Tile(int x, int y, ImageManager im, Game game, BufferedImage bi){
 this.oX = x;
 this.oY = y;
 this.im = im;
 this.game = game;
 this.bi = bi;
 }
 public abstract void tick();
 public abstract void render(Graphics g);
}
import java.awt.Graphics;
import java.awt.image.BufferedImage;
public class WalkableTerrainTile extends Tile{ 
 public WalkableTerrainTile(int x, int y, ImageManager im, Game game, BufferedImage bi) {
 super(x, y, im, game, bi);
 }
 public void tick() {
 this.game = game;
 x = oX + game.xOffset;
 y = oY + game.yOffset;
 }
 public void render(Graphics g) {
 g.drawImage(bi, x, y, Tile.TILESIZE * Game.SCALE, Tile.TILESIZE * Game.SCALE, null);
 }
}

Answer 1

I'm not sure if these would be optimized out by the compiler but

Tile.TILESIZE * SCALE
Tile.TILESIZE * Game.SCALE

are done more than once, why not just keep them as variables and...

for (int y = startY; y < finishY; y++) {
 for (int x = startX; x < finishX; x++) {
 map.tile.get((y*map.getMapWidth())+x).render(g);

...why do a multiplication for every y? you could just have a variable and increment it

int yLoc = startY * map.getWidth();
for (int y = startY; y < finishY; y++) {
 for (int x = startX; x < finishX; x++) {
 map.tile.get(yLoc+x).render(g);
 }
 yLoc += map.getMapWidth();
}

then you only need to do one multiplication and one addition for each y step instead of a multiplication for every y

• Bobby: Shouldn't the declaration of yloc be inside the first loop?
• Ross Drew: I think you mean the increment of yLoc. If the declaration was inside, then it would always be equal to the map width. I've fixed it
• Hayden: Ahh that is some good advice there. Thank you. I want to try and flesh out as much performance as I can.