## A

alpha channel
  The opacity of an image defined by an alpha value per pixel interleaved with the color components (for example, ARGB), an alpha value per pixel stored in a separate alpha surface, or a constant alpha value for the entire surface.
alpha color component
  The portion of a 32-bit color that determines its opacity. In this case, the alpha value per pixel is interleaved with the color components (for example, ARGB). Less commonly, this term can also refer to an image with an alpha value per pixel stored in a separate alpha surface.
alpha constant
  A level of opacity (alpha value) applied to an entire surface.
alpha edge blend
  A particular use of alpha blending (and alpha channel information) to reduce aliasing by blending edges based on pixel coverage information.
ambient
  A light source that illuminates everything in a scene, regardless of the orientation, position, and surface characteristics of the objects in the scene. Because this illuminates a scene with equal strength everywhere, the position and orientation of the frame it is attached to are inconsequential. Multiple ambient light sources are combined within a scene.
anisotropic filtering
  A mipmap filtering mode that compensates for anisotropy, which is the distortion visible in the texels of a 3D object whose surface is oriented at an angle with respect to the plane of the screen. The anisotropy is measured as the elongation (length divided by width) of a screen pixel that is inverse-mapped into texture space.
array object
  A group of objects organized into an array. Array objects make it simpler to apply operations to the entire group. The COM interfaces that allow you to work with array objects contain the GetElement and GetSize methods. These methods retrieve a pointer to an element in the array and the size of the array, respectively.
attach
  To connect multiple DirectDrawSurface objects into complex structures, like those needed to support 3-D page flipping with z-buffers. Attachment is not bidirectional, and a surface cannot be attached to itself. Emulated surfaces (in system memory) cannot be attached to nonemulated surfaces. Unless one surface is a texture map, the two attached surfaces must be the same size.
attached
  Physically connected to the system. A device may be installed but not currently attached.
attack
  The period at the beginning of a force feedback effect when the magnitude is reaching its basic or sustain level.
audio stream
  Sound data, mixed or unmixed. DirectSound mixes audio streams from each secondary sound buffer that is playing and writes the result to the primary sound buffer, which supplies the sound hardware with audio data.