[Solved] Lighting problem

OpenGL Development
#1

I’ve been working on my per-tile lighting system, currently it is very simple and supports coloured lighting.

PROBLEM 1:
I started to notice that lighting wouldn’t work for random tiles, here is an example:

http://screensnapr.com/e/9JoXox.png

At first i thought it was a problem in my tiling system, however if i disabled lighting the tiles were fine.

Here is my lighting code:


	public void updateLightValues() {
		for (Tile t : Engine.getMap().getVisibleTiles()) {
			Point p1 = new Point((int) x, (int) y);//Player coordinates
			double tileDistance = p1.distance((double) t.getX(), (double) t.getY());//the distance from the player to the tile
			tileDistance /= Tile.SIZE;//tiles are 16x16 therefore this is the amount of tiles between the player and the tile.
			if (tileDistance > lightDistance) continue;//if the distance is further than the light source's max distance, skip this tile.
			float light = lightDistance;//the initial light value (alpha value)
			light -= tileDistance;
			light /= 10;
			light += Engine.getMap().getLightModifier();//currently getlightmodifier() returns 0.
			if (light < 0) light = 0;
			if (light > 1) light = 1;

			float a = light + t.getLightValue() * (1 - light);
			float r = ((red * a) + (t.getLightRed() * t.getLightValue())) / a;
			float g = ((green * a) + (t.getLightGreen() * t.getLightValue())) / a;
			float b = ((blue * a) + (t.getLightBlue() * t.getLightValue())) / a;
			t.setLightValues(r, g, b, a);
		}
	}

That method is called every tick and will update light values around the light source.
Note that a light is represented by a LightSource, and the lightsource class holds all variables including this method.

PROBLEM 2:
My second problem is with the colour blending. It seems that a light source will blend into another light source, however the light source it’s blending into won’t be counter-blended, producing a weird blend like this:

http://screensnapr.com/e/diDBhS.png

Thankyou for your time.

#2

Lighting always has additive blending. If you shine two lights on a surface, it will emit twice as many photons. Your blending problem is probably because you modify the alpha which would affect all lights touching the tile.


float a = light + t.getLightValue() * (1 - light);
float r = ((red * a) + (t.getLightRed() * t.getLightValue())) / a;
float g = ((green * a) + (t.getLightGreen() * t.getLightValue())) / a;
float b = ((blue * a) + (t.getLightBlue() * t.getLightValue())) / a;

How is this going to do additive blending? The light intensity of a tile is the sum of all lights affecting it.

You can solve this by keeping the RGB intensity in each tile. You add the RGB color intensity from all lights affecting the tile (modified by distance, etc), and draw the tile with that color (which might be far over 1.0). You should know that your graphics card can do all this for you. Just create an FBO, add level-sized texture to it and draw the lights circles or a textured quad where you want them. You can even use the scissor test to only light the tiles that are actually visible on the screen, or even a smarter algorithm that has a smaller texture if you have a large/infinitely large world.

#3

<3!

Thanks alot for the info!