Shaders [Part 2]
(from Bonzai Engine)

•  Shader [Part 2]

The first part of this document has been dedicated to impressive rendering techniques.
This second part will present you more common shaders. Those shaders are all implemented with GLSL and integrated in the Bonzai Engine.

 

•  Opacity mapping

This effect is very simple. Instead of using a constant alpha (~ surface transparency) over all the surface, we uses a local alpha stored in a texture. This information can be stored in the alpha component of the diffuse texture, but there is lot of other ways.

For this screenshot, I've used a diffuse texture to get the rgb color. A second texture, the opacity texture, is used to get the local alpha value. This value is stored in the red component of the texture. This texture is below the screenshot.
 

Opacity Mapping

Opacity texture pattern

•  Normal Mapping

Here is a screenshots of this technique applied to the spawn model. Classic rendering of this model, ie with per-vertex lighting, can be seen here.
The body and the cape are shaded with double sided per pixel lighting and a normal map. Notice the local highlights and mesh details increased.
 

Spawn model rendered with normal mapping

•  Cube map reflection

The view ray is reflected on the object surface (a teapot here). The reflected vectors is used for the texture look-up in a a cube map texture. A cube map textures is a texture made of 6 textures, each texture for a side of a cube (+x, -x, +y, -y, +z & -z). Depending on the vector, one of the 6 textures is selected for the color look-up.
 

Cube Map Reflection

•  Cube map refraction

This effect is similat to the cube map reflection. Instead of reflecting the view ray, it is refracted depending on the surface internal/external indices. The refracted vector is used in the same way for the cube map texture look-up.
 

Cube Map Refraction

Note: The cube map used for this screenshot is the same than the one used for the cube map reflection screenshot.
 

•  Sphere map reflection

The view ray reflection is done similarly to the cbe map reflection shader. But, instead of using a cube map textures (ie ~ 6 textures) we only uses a single 2D texture. So the look-up is little bit different here. The reflected vector is used to generate a vector suitable for making a sphere map texture look-up.
 

Sphere map reflection

•  Sphere map refraction

Well, all the thing are explained in the previous shader screenshots, see here the result :
 

Sphere map refraction

•  Shaders - Screenshots

•  F40

The F40 model uses different kind of shaders, all presented previously. You can see the huge improvement on the rendering.

The tires are rendered with normal mapping for the tires to add roughness on the flat surface. A sphere map reflection shader is apply to practically all parts of the car. An opacity map is used for the top of the windscreen and the grids located on the front and rear bumpers.
 

F40 with & without the use of shaders

•  Zippo

The body of the zippo is renderer with using a normal map for light calculation and a reflection.
The animation loop of the picture below :
 - Body with diffuse color.
 - Body with Reflection mapping
 - Body with Normal mapping
 - Body with Normal mapping + Reflection mapping
 

Zippo: Normal + Reflection mapping