Hello & Questions

[lisa]

With the glow map applied:

[lisa]

Environment Map

An environment map is a texture map that contains images of what is in the environment around the model, versus an image that is part of the model itself.
An environment map contains a 360 degree panorama of what the model can see.

Just like a specular map, the effects of an environment map are view-angle dependent. Where the viewer is in relation to the object and the camera will cause different parts of the environment map to be shown.

Many games and renderers will generate environment maps "on the fly" by rendering a panoramic image of the scene from the point of view of the model. This makes the reflections more realistic, because it then appears as if the model were actually reflecting the other objects in the scene.

However, "static" environment maps are common, too. Artists will use an image of the sky or other picture as an environment map when there are no other objects in the scene, to achieve special effects or when rendering environment maps on the fly is too slow.

[lisa]

This reflection map indicates which parts of the cube should be subject to environment mapping. Like the specular power map, this type of map is somewhat unusual. Most people just make the whole object reflective:

[lisa]

Unfortunately, it is difficult to convey the effect of an environment map in a still image, but here are a couple of different views of the cube with only environment mapping enabled:

[lisa]

Displacement Map

A displacement map measures the amount to displace, or move, the geometry at the specified point. Brighter pixels move the geometry upwards or away from the surface, and darker pixels move the geometry downwards or toward the surface.

Many landscape editors use displacement maps to indicate the height of the terrain at a particular point. Displacement maps used in this way are often referred to as "height maps".

Most displacement maps are grayscale and only measure the displacement of a point on a single axis. However, it is possible to make a displacement map that moves a point on all three axes. "Sculpted prims" in Second Life are one such example of a 3D displacement map. Coloring the red channel causes the point to move on the x axis, coloring the green channel causes the point to move on the y axis, and coloring the blue channel causes the point to move on the z axis.

My cube shader is not capable of displacing geometry using a displacement map. However, it still uses a displacement map for something else even cooler I'll show you in a moment.

[lisa]

Bump Map or Normal Map

One of the downsides of a displacement map is that it needs one vertex for every point you want to displace. If you have many fine details this can eat up a lot of memory and slow down your game or render unacceptably. Bump mapping is a technique that lets you re-create the *appearance* of a displacement map without the performance penalty.

A bump map is a grayscale image that often looks similar or identical to a displacement map. In fact, the same image can often be used interchangeably as a displacement map or a bump map. However, unlike a displacement map, a bump map does not actually alter the geometry of the model. Instead, it alters the model's surface normals.

A surface normal is used by the renderer to calculate the angle between a surface and a light, so that the renderer knows how much light the surface should receive. By perturbing these surface normals, a bump map causes shadows to appear on the surface of the model as if it were covered in fine details. Because the human eye relies on light and shadow so heavily as an indicator of depth, the appearance of these shadows can convince the mind that the shapes are really there, even though no such details exist.

Bump maps aren't a 100% replacement for displacement maps. Because they only change the shadows, not the geometry, they can't be used for large bumps or anything that would change the silhouette of the model. However, for small details they can be very effective.

A normal map is a more advanced type of bump map. Whereas a bump map merely bends the existing surface normal, a normal map allows you to replace it entirely. Each RGB value in a normal map represents the new XYZ vector of the surface normal at that pixel. This allows you to create more convincing illusions of shape that are not possible with traditional bump maps.

Normal maps can be in "object space" or in "tangent space". Object space normal maps have the XYZ values relative to the object. These normal maps usually appear multi-colored. They are faster to render, but can't be easily used for animation and they can't be tiled. Tangent space normal maps have the XYZ values relative to each surface. They usually appear bluish in color. These type of normal maps are more common because they are more flexible to use.

The effects of a normal map can be *very* dramatic. Many modern games use normal maps to give the illusion of much higher resolution geometry than the game is actually capable of. The effect is often so convincing that it is difficult for players to discern a high resolution model from a lower-resolution normal mapped model even when they are placed side-by-side.

[lisa]

The cube with normal mapping applied: