Image

Defines and holds a 1D/2D/3D image and optionally a mipmap pyramid and/or a list of equally sized frames with a single frameDelay. Various pixelTypes are supported to handle gray and RGB color images with or without alpha channel.

An Image is only a container for the pixel data and image description. It does not create or handle any OpenGL state elements. However, image objects are utilized to handle the data for texture (e.g. osg::SimpleTextureMaterial or osg::TextureChunk) or bitmap objects (e.g. osg::ImageForeground).

The image object holds some describing fields (e.g. width/height/depth), and a single block of memory for all the raster data.

Mem layout for Multi-Frame mip-map image data

The image data starts in the lower left (front) corner and all bytes for a single pixel (e.g. RGB) are stored sequentially in memory. They are not organized in separate layers or channels.

The optional mipmap-level are stored directly after the Image data. The dimensions (width/height/depth) are always reduced to 50% of the previous level but stay at least 1. The Image object can hold just a number of levels and must not be complete (end with a 1x1x1 level).

If there are any additional mipmap-levels defined, OpenSG will use the data turing the texture-upload process. If the image does not contain mipmap levels, which is true in most cases, OpenSG will use OpenGL functions to create the level direclty as OpenGL objects. The System will not change the image object for rendering. Therefore, the ability to define the mipmap levels is rarely needed but very usefull (e.g. Real-Time Hatching).

The pyramid (at least one Level) defines a frame. All frames are stored after each other separately starting with frame 0.

If the user loads a multi-frame image and assigns the object to a osg::TextureChunk it is not played automatically as movie. The Application has to set and change the 'current' frame in the TextureChunk.

The Image Class implementation does not include Image-Processing functionality, but provides some simple funktions to scale and crop and to set subregions of the data.

The system provides loaders and writers for various formats including png, jpeg, tiff, gif and sgi. In addition a specific mtd (multi texture data) reader/writer is included. The mtd file format is a simple platform independent header and binary dump of the Image object data. It is the only format which can hold all field and data properties of the OpenSG Image.

The graph loaders (e.g. OSGLoader, VRMLLoader) use the image loaders to fetch the raster data.

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