1. Overlays
2. Decals

What are Overlays?

Overlays are simple, flat "decorations" that the mappers can apply to most textured surfaces. One obvious example is the graffiti you see on the walls and the hostage rescue zone demarcation on the ground in hostage maps. In addition, overlays can be more subtle. Scattered leaves on a grassy knoll, a storm drain in the basement, a rusty pipe hole on the wall are all overlays. They can greatly enrich a map and add significant realism to it. And best of all, they are pretty simple to apply and they do not hinder the performance of the map.

Applying Overlays

We'll be working with firstmap again, so open it up. Press Shift-O to activate the Overlay Tool. Open the Texture Browser, and type "overlay" or "decal" in the filter. Alternatively, you can also type in the kind of overlay you're searching for in the filter. For example, type in "graffiti" in the filter to browse all the graffiti you can apply to your map.

After you've selected the overlay you want, it's a matter of left-clicking in the 3D camera view of the map to apply it. The overlay shows up instantly once you applied it. If you think the overlay appears off-centered in the map, simply turn to the Select Tool, click on the central red box of the overlay, and adjust the position.

For practice, apply the "overlays/rug001a" (filter "rug overlay") to our small indoor room. Select the overlay and rotate it (click on the overlay in the 2D view twice--not double-click--and drag the small white handles around the selected overlay to rotate it). If it's off centered, select it and drag it to re-position it. The result should look like this in the 3D view:

Rug overlay

In addition, let's put some graffiti on the outside wall. Pick the overlay "decals/decalgraffiti023a" (filter "graffiti") and apply it to the wall next to the door texture.

Graffiti overlay - reversed

Aligning Overlays

You probably noticed that the graffitied words are flipped around for some reason. We can fix this easily. With the Selection Tool (Shift-S), select the overlay and bring up the properties box. Overlays utilize a UV coordinate system. For this system, (0,0) is the top left corner of the texture and (1,1) is the bottom right corner. We can enter other values such as 0.5 or 2 for the UV End values to get only portions of the texture or multiple repeats of the pattern in a single overlay.

Most commonly, we need to flip the overlay to its mirror image. To flip the image, use a negative values for the "U End" value. If we put -1 as the "U End" value, we can see that our reversed graffiti is displayed correctly now.

Reshaping and Resizing Overlays

Let's apply some trashy overlays in the outside area. From the Texture Browser, select "decals/trashdecal01a" (filter "trash decal"), and apply the overlay to the North corner or the corridor, as shown below:

Trash overlay

It would look more realistic if the trash were piled up against the corner of the wall, as wind would cluster them together that way. So let's select the overlay, and reshape the bounding box of the overlay by dragging the white handles around the selected overlay.

Trash overlay re-positioned

In additon, if an overlay is applied to a displacement surface, modifying the shape of the displacement would affect the overlay as well. The overlay automatically conforms to the shape of the displacement surface. This is an added benefit for overlays that decals do not have.