glCompressedTexImage2D(3) specify a two-dimensional texture image in a compressed format

C SPECIFICATION

void glCompressedTexImage2D(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, GLsizei imageSize, const GLvoid * data);

PARAMETERS

target

Specifies the target texture. Must be GL_TEXTURE_2D, GL_PROXY_TEXTURE_2D, GL_TEXTURE_1D_ARRAY, GL_PROXY_TEXTURE_1D_ARRAY, GL_TEXTURE_CUBE_MAP_POSITIVE_X, GL_TEXTURE_CUBE_MAP_NEGATIVE_X, GL_TEXTURE_CUBE_MAP_POSITIVE_Y, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, GL_TEXTURE_CUBE_MAP_POSITIVE_Z, GL_TEXTURE_CUBE_MAP_NEGATIVE_Z, or GL_PROXY_TEXTURE_CUBE_MAP.

level

Specifies the level-of-detail number. Level 0 is the base image level. Level n is the nth mipmap reduction image.

internalformat

Specifies the format of the compressed image data stored at address data.

width

Specifies the width of the texture image. All implementations support 2D texture images that are at least 64 texels wide and cube-mapped texture images that are at least 16 texels wide.

height

Specifies the height of the texture image. All implementations support 2D texture images that are at least 64 texels high and cube-mapped texture images that are at least 16 texels high.

border

This value must be 0.

imageSize

Specifies the number of unsigned bytes of image data starting at the address specified by data.

data

Specifies a pointer to the compressed image data in memory.

DESCRIPTION

Texturing allows elements of an image array to be read by shaders.

glCompressedTexImage2D loads a previously defined, and retrieved, compressed two-dimensional texture image if target is GL_TEXTURE_2D, or one of the cube map faces such as GL_TEXTURE_CUBE_MAP_POSITIVE_X. (see glTexImage2D()).

If target is GL_TEXTURE_1D_ARRAY, data is treated as an array of compressed 1D textures.

If target is GL_PROXY_TEXTURE_2D, GL_PROXY_TEXTURE_1D_ARRAY or GL_PROXY_CUBE_MAP, no data is read from data, but all of the texture image state is recalculated, checked for consistency, and checked against the implementation's capabilities. If the implementation cannot handle a texture of the requested texture size, it sets all of the image state to 0, but does not generate an error (see glGetError()). To query for an entire mipmap array, use an image array level greater than or equal to 1.

internalformat must be a known compressed image format (such as GL_RGTC) or an extension-specified compressed-texture format. When a texture is loaded with glTexImage2D() using a generic compressed texture format (e.g., GL_COMPRESSED_RGB), the GL selects from one of its extensions supporting compressed textures. In order to load the compressed texture image using glCompressedTexImage2D, query the compressed texture image's size and format using glGetTexLevelParameter().

If a non-zero named buffer object is bound to the GL_PIXEL_UNPACK_BUFFER target (see glBindBuffer()) while a texture image is specified, data is treated as a byte offset into the buffer object's data store.

If the compressed data are arranged into fixed-size blocks of texels, the pixel storage modes can be used to select a sub-rectangle from a larger containing rectangle. These pixel storage modes operate in the same way as they do for glTexImage2D(). In the following description, denote by bs, bw, bh, and bd, the values of pixel storage modes GL_UNPACK_COMPRESSED_BLOCK_SIZE, GL_UNPACK_COMPRESSED_BLOCK_WIDTH, GL_UNPACK_COMPRESSED_BLOCK_HEIGHT, and GL_UNPACK_COMPRESSED_BLOCK_DEPTH, respectively. bs is the compressed block size in bytes; bw, bh, and bd are the compressed block width, height, and depth in pixels.

By default the pixel storage modes GL_UNPACK_ROW_LENGTH, GL_UNPACK_SKIP_ROWS, GL_UNPACK_SKIP_PIXELS, GL_UNPACK_IMAGE_HEIGHT and GL_UNPACK_SKIP_IMAGES are ignored for compressed images. To enable GL_UNPACK_SKIP_PIXELS and GL_UNPACK_ROW_LENGTH, bs and bw must both be non-zero. To also enable GL_UNPACK_SKIP_ROWS and GL_UNPACK_IMAGE_HEIGHT, bh must be non-zero. To also enable GL_UNPACK_SKIP_IMAGES, bd must be non-zero. All parameters must be consistent with the compressed format to produce the desired results.

When selecting a sub-rectangle from a compressed image:

• the value of GL_UNPACK_SKIP_PIXELS must be a multiple of bw;.RE

• the value of GL_UNPACK_SKIP_ROWS must be a multiple of bw..RE

imageSize must be equal to:

b s × width b w × height b h

ERRORS

GL_INVALID_ENUM is generated if internalformat is not one of the generic compressed internal formats: GL_COMPRESSED_RED, GL_COMPRESSED_RG, GL_COMPRESSED_RGB, GL_COMPRESSED_RGBA. GL_COMPRESSED_SRGB, or GL_COMPRESSED_SRGB_ALPHA.

GL_INVALID_VALUE is generated if imageSize is not consistent with the format, dimensions, and contents of the specified compressed image data.

GL_INVALID_VALUE is generated if border is not 0.

GL_INVALID_OPERATION is generated if parameter combinations are not supported by the specific compressed internal format as specified in the specific texture compression extension.

GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_UNPACK_BUFFER target and the buffer object's data store is currently mapped.

GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_UNPACK_BUFFER target and the data would be unpacked from the buffer object such that the memory reads required would exceed the data store size.

Undefined results, including abnormal program termination, are generated if data is not encoded in a manner consistent with the extension specification defining the internal compression format.

ASSOCIATED GETS

glGetCompressedTexImage()

glGet() with argument GL_TEXTURE_COMPRESSED

glGet() with argument GL_PIXEL_UNPACK_BUFFER_BINDING

glGetTexLevelParameter() with arguments GL_TEXTURE_INTERNAL_FORMAT and GL_TEXTURE_COMPRESSED_IMAGE_SIZE

COPYRIGHT

Copyright © 1991-2006 Silicon Graphics, Inc. © 2011 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see m[blue]http://oss.sgi.com/projects/FreeB/m[].

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