What Is a Configurable Effect?

Artikel
09/29/2011

A configurable effect is an optimized rendering effect designed for Windows, Xbox 360, and Windows Phone. A configurable effect is created using a built-in object with options for user configuration.

A configurable effect is an easy way to get started rendering effects. There are several built-in configurable effects which have been designed to run efficiently on mobile GPU hardware. These effects are also available on Windows and Xbox 360, where they can be a useful starting point for developers who do not want to write their own custom shaders. Use a configurable effect in a game designed for the Reach or HiDef profile.

Use one of the following configurable effects to implement these rendering effects:

Basic Lighting and Fog
Character Animation
More Sophisticated Lighting with a Light Map
Billboards and Imposters
Lighting Highlights Using an Environment Map

Basic Lighting and Fog

Use the BasicEffect configurable effect to implement general purpose functionality, including the following: transformations; lighting with three directional lights; material colors using ambient, diffuse, and specular properties; a single texture; and fog. To improve speed, fog calculations are based on depth instead of distance from the camera. When you choose a basic effect, you can improve the performance of your game if you don't use any fog or if you only use one of the three available directional lights. For an example, see Creating a Basic Effect.

Character Animation

Use the SkinnedEffect configurable effect to animate a character. This effect uses bones and weights to transform a mesh (an object is made up of several meshes). Simply set up a set of bones for a model when you create content, and then transform the bones during the render loop. You can also use this class for hardware instancing by setting WeightsPerVertex to one, and replicating the geometry data with an additional bone index channel. This is similar to the way the shader instancing technique works in the instancing sample.

More Sophisticated Lighting with a Light Map

Use the DualTextureEffect configurable effect with a prebaked radiosity lightmap to add more sophisticated lighting to a scene. This effect uses two textures, the base texture with the texture detail and an overlay texture with the prebaked lighting.

The two textures are combined using a fixed modulate2X blend formula as shown here:

      result.rgb = x.rgb * y.rgb * 2;
      result.a = x.a * y.a;

Billboards and Imposters

Use the AlphaTestEffect configurable effect to use alpha data to test whether to draw a pixel. The effect uses a CompareFunction to compare the alpha value for a pixel against the ReferenceAlpha value to determine whether to draw the pixel. This functionality is used for drawing a billboard (a 2D sprite that faces the camera) and an imposter (a 2D sprite that is integrated into a larger scene).

Lighting Highlights Using an Environment Map

Use the EnvironmentMapEffect configurable effect to generate fast, specular highlights that add shininess to an object. The effect uses two textures, a base texture with the texture detail and a cubemap whose six sides reflect the environment onto the object. Use EnvironmentMapAmount to control the amount of the environment map to add to the object. Also, use FresnelFactor to control how much the edge of an object reflects specular lighting.

Pseudo code for the lighting calculations looks similar to this:

      viewAngle = dot(eyeToVertexVector, vertexNormal);
      fresnel = saturate(pow(1 – abs(viewAngle), FresnelFactor);
      amount = fresnel * EnvironmentMapAmount;
      result.rgb = lerp(diffuseTexture.rgb, cubeTexture.rgb, amount);
      result.rgb += cubeTexture.a * EnvironmentMapSpecular

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