1Name 2 3 SGIX_interlace 4 5Name Strings 6 7 GL_SGIX_interlace 8 9Version 10 11 $Date: 1995/02/22 20:58:22 $ $Revision: 1.2 $ 12 13Number 14 15 45 16 17Dependencies 18 19 None. 20 21Overview 22 23 This extension provides a way to interlace rows of pixels when 24 rasterizing pixel rectangles, and loading texture images. In this 25 context, interlacing means skiping over rows of pixels or texels 26 in the destination. This is useful for dealing with video data 27 since a single frame of video is typically composed from two images 28 or fields: one image specifying the data for even rows of the frame 29 and the other image specifying the data for odd rows of the frame. 30 31New Procedures and Functions 32 33 None. 34 35New Tokens 36 37 Accepted by the <cap> parameter of of Enable, Disable, IsEnabled, 38 and by the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, 39 GetDoublev: 40 41 INTERLACE_SGIX 0x8094 42 43Additions to Chapter 2 of the 1.0 Specification (OpenGL Operation) 44 45 None. 46 47Additions to Chapter 3 of the 1.0 Specification (Rasterization) 48 49 The specification of interlace operation is added the GL Specification 50 in section 3.6.3 "Rasterization of Pixel Rectangles", immediately 51 following the operations described by EXT_histogram, and immediately 52 prior to the subsection "Final Conversion". 53 54 The interlacing of rows of pixels is enabled or disabled with Enable or 55 Disable using the symbolic constant INTERLACE_SGIX. If INTERLACE_SGIX 56 is enabled, then all of the groups which belong to a row m are treated 57 as if they belonged to the row 2 * m. If the source image has a height 58 of h rows, this effectively expands the height of the image to 2 * h - 1 59 rows. After interlacing, only every other row of the image is defined. 60 If the interlaced pixel rectangle is rasterized to the framebuffer, then 61 only these rows are converted to fragments. If the interlaced pixel 62 rectangle is a texture image, then only these rows are written to texure 63 memory. 64 65 In cases where errors can result from the specification of invalid 66 image dimensions, it is the resulting dimensions that are tested, not 67 the dimensions of the source image. (A specific example is TexImage2D, 68 which specifies constraints for image dimensions. Even if TexImage2D 69 is called with a null pixel pointer, the dimensions of the resulting 70 texture image are those that would result from the effective expansion 71 of the specified image due to interlacing.) 72 73Additions to Chapter 4 of the 1.0 Specification (Per-Fragment Operations 74and the Frame Buffer) 75 76 In section 4.3 "Drawing, Reading, and Copying Pixels" 77 78 INTERLACE_SGIX has no effect on the operation of ReadPixels. 79 80Additions to Chapter 5 of the 1.0 Specification (Special Functions) 81 82 None. 83 84Additions to Chapter 6 of the 1.0 Specification (State and State Requests) 85 86 None. 87 88Additions to the GLX Specification 89 90 None. 91 92Errors 93 94 None. 95 96New State 97 98 Get Value Get Command Type Initial Value Attribute 99 --------- ----------- ---- ------------- --------- 100 INTERLACE_SGIX IsEnabled B False pixel/enable 101 102New Implementation Dependent State 103 104 None. 105