Time for action – using ambient light

To implement ambient light, perform the following steps:

1. 1. Add two more declarations to the declarations area of the Terrain.fx effect file:

   float4 ambientLightColor;
   float ambientLightLevel;

2. 2. In the PixelShaderFunction() of the Terrain.fx file, just before setting the alpha value of the pixel to 1.0 add the following line of code:

   pixelColor += (ambientLightColor * ambientLightLevel);

3. 3. In the Draw() method of the Terrain class, add two additional parameter settings before the terrain is drawn:

   effect.Parameters["ambientLightLevel"].SetValue(0.15f);
   effect.Parameters["ambientLightColor"].SetValue(
       new Vector4(1,1,1,1));

4. 4. Execute the game and view the newly lit terrain. The game should look like the following screenshot:

   

What just happened?

That certainly looks better! The dark areas are still dark, but they haven't completely lost their detail now. Ambient lighting is quite a bit simpler to implement than diffuse lighting. All we need to know is...