2D Lighting Glitch

Question

I've been working on a game in Java, and recently I decided to try out my game on a netbook just to see how it would run. While I do get a constant and decent FPS, it appears that my lighting rendering decides to freak out a bit. This only happens on the netbook, however, and I'm not sure how I can fix it.

Here's the lighting glitch:

I'm doing my lighting simply by drawing black rectangles with certain alpha values over each tile.

As you can see, for some reason there are sometimes vertical and (although not shown) horizontal lines that the alpha rectangles apparently aren't drawing over.

The lines flicker on and off as I move around, and placing two blocks on top of each other prevents the glitch for those blocks.

I'm using Graphics to draw on a JFrame, and the block rendering code looks like this:

g.drawImage(sprite, (int)x, (int)y, null);
g.setColor(new Color(0,0,0,<insert darkness level>));
g.fillRect((int)x,(int)y,32,32);

Someone on another forum thought it could be rounding errors with the block positions, but all the blocks are snapped to a 32x32 grid on creation.

I'm not sure there's anything wrong with the code itself, which is why I'm not sure how to fix this. If someone could help, I'd be really, really grateful, because I'm truly stuck here. Thank you in advance!

Answer 1

This sounds to me like a pixel mapping issue. First try varying the resolution to see if the problem appears on other systems and whether a resolution change affects it on the problematic device.

When rendering the sprite needs to be mapped to screen space. Let's say its a 400x400 resolution and your drawing 12 blocks horizontally. That means your 32 width rectangle maps into 400/12 pixels which comes out as 33.33. Not very nice.

But we can't do a third of a pixel, although that would be nice, so we hope that while some are rounded down to 33, the others are rounded up to span 34 pixels thus leaving no gap. However that doesn't happen. So the best way to handle this is to make sure the resolution is always a power of 2 and so are our sprites. That should make them map directly.

Note: I mention this because the sample image seems to be 378x368 pixels.

Answer 2

I know this is old, but I finally discovered the solution. In my game, I am using g.translate(x,y); but I was using a float for the x and y values. So I did this:

g.translate(Math.round(transX),Math.round(transY);

Now there are no more vertical lines! Hopefully this helps anyone else with this problem.