GLOW MAPS

This information comes courtesy of Derf Davies. It is a formula for changing the colour of a texture using light intensity as a control.

A glow map is a second texture placed over the first that resists change in light intensities. Now you're probably thinking, 'What use is that at all?' Especially since you cannot change the opacity of a glow map and not the opacity of the underlying texture at the same time via MML. (I am getting somewhere, trust me.)

There is another way to change that, using a mask with gray areas indicating semi-transparent areas. Why people have not been using this to create weapon sprites with semi-transparent firing flares is beyond me. This would remove the giant bubble of fire present in the shotgun sequence. ANYWAY...

What follows is a somewhat complex but very effective way of changing texture colour. This originally came from the idea of having the sun go down, and the textures would change from normal or somewhat yellow colouring to dark blue, simulating nighttime (considering that very dark textures in Marathon are only realistic in indoor areas).

Say you have texture A, a piece of metal:

1. Go into Photoshop, open the channels palette and knock off the blue channel. The texture should seem rather yellow now.

2. Screenshot this, open it, and trim it. This is your base texture.

3. Open your original texture and then (using the channels palette) knock off the red and green channels. You should get a greyscale representation of the blue intensity in the texture. (I'm using Photoshop 4; you may get a blue texture in later editions, I don't know.) You want to make this blue, so paint a perfectly blue square as large as the texture, overlay the greyscale relief and turn the layer mode to "darken". This should now represent all the blue shades in the texture.

Hope I'm not losing you.

4. You may notice that we now have a texture in two parts - a blue part, and a red and green part (yellow). If we were to add the two, we would get an accurate portrayal of the normal texture. This is what we have to do inside the Marathon engine.

5. Create another file, totally grey (50% brightness I think). Save this as the blue texture's mask. You should now have three files...
• Texture A's base (yellow)
• Texture A's overlay (blue)
• Texture A's overlay's mask (plain grey)

6. String these files together with MML making the normal_image the base, the glow_image the overlay, and the glow_mask the overlay's mask.

7. Place down the texture in Marathon and alter the lighting. At 100%, the blue and yellow combine to show a normal metal texture. At 0%, the metal is dark blue, as the yellow is too dark, and the blue is the glow image and will not change in intensity.

Whew!!! This actually works, and when you master it and figure out how it works, you will find that you can change the texture's colour to anything, you just have to split the channels the right way. A whole level can go red with emergency lights, etc. However, if you want the change to be dramatic, all lights in the area have to be at 100%, otherwise the change will start to be implemented.