A texture is a rectangular array of colored pixels. (The rectangle does not necessarily have to be square, although the system deals most efficiently with square textures.) You can use textures for texture-mapping faces, in which case their dimensions must be powers of two.
An IDirect3DRMTexture interface is actually an interface to a DirectDrawSurface object, not to a distinct Direct3D texture object. For more information about the relationship between textures in Direct3D and surfaces in DirectDraw, see Direct3D Texture Interface.
Your application can use the IDirect3DRM::CreateTexture method to create a texture from a D3DRMIMAGE structure, or the IDirect3DRM::CreateTextureFromSurface method to create a texture from a DirectDraw surface. The IDirect3DRM::LoadTexture method allows your application to load a texture from a file; the texture should be in Windows bitmap (.bmp) or Portable Pixmap (.ppm) format.
The texture coordinates of each face define the region in the texture that is mapped onto that particular face. Your application can use a wrap to calculate texture coordinates. For more information, see Direct3DRMWrap.
Decals
Textures can also be rendered directly, as visuals. Textures used this way are sometimes known as decals, a term adopted by Retained Mode. A decal is rendered into a viewport-aligned rectangle. The rectangle can optionally be scaled by the depth component of the decal's position. The size of the decal is taken from a rectangle defined relative to the containing frame by using the IDirect3DRMTexture::SetDecalSize method. (An application can retrieve the size of the decal by using the IDirect3DRMTexture::GetDecalSize method.) The decal is then transformed and perspective projection is applied.
Decals have origins that your application can set and retrieve by using the IDirect3DRMTexture::SetDecalOrigin and IDirect3DRMTexture::GetDecalOrigin methods. The origin is an offset from the top-left corner of the decal. The default origin is [0, 0]. The decal's origin is aligned with its frame's position when rendering.
Texture Colors
You can set and retrieve the number of colors that are used to render a texture by using the IDirect3DRMTexture::SetColors and IDirect3DRMTexture::GetColors methods.
If your application uses the RGB color model, you can use 8-bit, 24-bit, and 32-bit textures. If you use the monochromatic (or ramp) color model, however, you can use only 8-bit textures.
Several shades of each color are used when lighting a scene. An application can set and retrieve the number of shades used for each color by calling the IDirect3DRMTexture::SetShades and IDirect3DRMTexture::GetShades methods.
A Direct3DRMTexture object uses a D3DRMIMAGE structure to define the bitmap that the texture will be rendered from. If the application provides the D3DRMIMAGE structure, the texture can easily be animated or altered during rendering.
Mipmaps
A mipmap is a sequence of textures, each of which is a progressively lower resolution, prefiltered representation of the same image. Mipmapping is a computationally low-cost way of improving the quality of rendered textures. Each prefiltered image, or level, in the mipmap is a power of two smaller than the previous level. You can specify mipmaps when filtering textures by calling the IDirect3DRMDevice::SetTextureQuality method.
For more information about how to use DirectDraw to create mipmaps, see Mipmaps.
Texture Filtering
After a texture has been mapped to a surface, the texture elements (texels) of the texture rarely correspond to individual pixels in the final image. A pixel in the final image can correspond to a large collection of texels or to a small piece of a single texel. You can use texture filtering to specify how to interpolate texel values to pixels.
You can use the IDirect3DRMDevice::SetTextureQuality method and the D3DRMTEXTUREQUALITY enumerated type to specify the texture filtering mode for your application.
Texture Transparency
You can use the IDirect3DRMTexture::SetDecalTransparency method to produce transparent textures. Another method for achieving transparency is to use DirectDraw's support for color keys. Color keys are colors or ranges of colors that can be part of either the source or destination of a blit or overlay operation. You can specify that these colors should always be overwritten or never be overwritten.
For more information about DirectDraw's support for color keys, see Color Keying.
For related information, see IDirect3DRMTexture.