Question

I have my game which, on every render loop, loops through all the blocks in my map (128×128) which as you can probably tell, causes a lot of lag. When I first made it, I had to make it render only the blocks on the screen, or it would crash instantly. Now I only render the blocks on the screen, but still loop through all the blocks to see if they are on the screen, which makes my fps about 2.

    for (int y = 0; y < 128; y++) {
        for (int x = 0; x < 128; x++) {
            Block b = LevelGen.getBlockAt(x, y);
            if (Forgotten.isInsideGameWindow(x * 30, y * 30)) {
                arg1.drawImage(b.getTexture(), x * 30, y * 30);
            }
        }
    }

Is there a way to make it so doesn’t loop through all of them?

Answer 1

Figure out the size of your display window, and only iterate blocks that are within it.

final int tile_size = 30;

final RectangleType displayWindow = Forgotten.getDisplayWindow ();

final int left = displayWindow.getLeft () / tile_size - 1;
final int right = displayWindow.getRight () / tile_size + 1;
final int top = displayWindow.getTop () / tile_size - 1;
final int bottom = displayWindow.getBottom () / tile_size + 1;

for (int y = top; y < bottom; ++y)
   for (int x = left; x < right; ++x)
       canvas.drawImage (LevelGen.getBlockAt (x,y).getTexture (),
                         x * tile_size, y * tile_size);

You may also want to figure out which area(s) of the canvas actually want to be drawn, and instead keep a “dirty rectangle” list of areas to be redrawn. Whenever a tile changes, or a sprite/particle/whatever passes through its space, add that tile to the rectangle. Even if you just use a single dirty rectangle that enlarges to encompass all updates during a frame, if your game doesn’t actually have “stuff happening” at all points on the display at all times, your frame rate will be higher on average (but suffer from large-scale effects)

expanding upon that:

      public class Map {
            private Rectangle dirtyRect = null;

            public void dirty (Rectangle areaAffected) {
                   if (null == dirtyRect) {
                        dirtyRect = areaAffected; return;
                   }
                   dirtyRect = new Rectangle ( Math.min (dirtyRect.getLeft (),
                                                         areaAffected.getLeft () ),
                                               Math.min (dirtyRect.getTop (),
                                                         areaAffected.getTop () ),
                                               Math.max (dirtyRect.getRight (),
                                                         areaAffected.getRight () ),
                                               Math.max (dirtyRect.getBottom (),
                                                         areaAffected.getBottom () ));
            }

Then use the dirty rectangle in place of displayWindow for normal draws, and you can test if (null == getDirtyRectangle ()) return; to skip drawing at all if nothing’s changed.