Name SGIX_interlace Name Strings GL_SGIX_interlace Version $Date: 1995/02/22 20:58:22 $ $Revision: 1.2 $ Number 45 Dependencies None. Overview This extension provides a way to interlace rows of pixels when rasterizing pixel rectangles, and loading texture images. In this context, interlacing means skiping over rows of pixels or texels in the destination. This is useful for dealing with video data since a single frame of video is typically composed from two images or fields: one image specifying the data for even rows of the frame and the other image specifying the data for odd rows of the frame. New Procedures and Functions None. New Tokens Accepted by the parameter of of Enable, Disable, IsEnabled, and by the parameter of GetBooleanv, GetIntegerv, GetFloatv, GetDoublev: INTERLACE_SGIX 0x8094 Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation) None. Additions to Chapter 3 of the 1.0 Specification (Rasterization) The specification of interlace operation is added the GL Specification in section 3.6.3 "Rasterization of Pixel Rectangles", immediately following the operations described by EXT_histogram, and immediately prior to the subsection "Final Conversion". The interlacing of rows of pixels is enabled or disabled with Enable or Disable using the symbolic constant INTERLACE_SGIX. If INTERLACE_SGIX is enabled, then all of the groups which belong to a row m are treated as if they belonged to the row 2 * m. If the source image has a height of h rows, this effectively expands the height of the image to 2 * h - 1 rows. After interlacing, only every other row of the image is defined. If the interlaced pixel rectangle is rasterized to the framebuffer, then only these rows are converted to fragments. If the interlaced pixel rectangle is a texture image, then only these rows are written to texure memory. In cases where errors can result from the specification of invalid image dimensions, it is the resulting dimensions that are tested, not the dimensions of the source image. (A specific example is TexImage2D, which specifies constraints for image dimensions. Even if TexImage2D is called with a null pixel pointer, the dimensions of the resulting texture image are those that would result from the effective expansion of the specified image due to interlacing.) Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations and the Frame Buffer) In section 4.3 "Drawing, Reading, and Copying Pixels" INTERLACE_SGIX has no effect on the operation of ReadPixels. Additions to Chapter 5 of the 1.0 Specification (Special Functions) None. Additions to Chapter 6 of the 1.0 Specification (State and State Requests) None. Additions to the GLX Specification None. Errors None. New State Get Value Get Command Type Initial Value Attribute --------- ----------- ---- ------------- --------- INTERLACE_SGIX IsEnabled B False pixel/enable New Implementation Dependent State None.