glCompressedTexImage2D

glCompressedTexImage2D: man4/glCompressedTexImage2D.xml

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_TEXTURE_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 b s, b w, b h, and b d, 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. b s is the compressed block size in bytes; b w, b h, and b d 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, b s and b w must both be non-zero. To also enable GL_UNPACK_SKIP_ROWS and GL_UNPACK_IMAGE_HEIGHT, b h must be non-zero. To also enable GL_UNPACK_SKIP_IMAGES, b d 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:

1. The value of GL_UNPACK_SKIP_PIXELS must be a multiple of b w;
2. the value of GL_UNPACK_SKIP_ROWS must be a multiple of b w.

imageSize must be equal to: b s × width b w × height b h

The specific compressed internal formats GL_COMPRESSED_RGB8_ETC2, GL_COMPRESSED_SRGB8_ETC2, GL_COMPRESSED_RGB8_PUNCHTHROUGH_ALPHA1_ETC2, GL_COMPRESSED_SRGB8_PUNCHTHROUGH_ALPHA1_ETC2, GL_COMPRESSED_RGBA8_ETC2_EAC, GL_COMPRESSED_SRGB8_ALPHA8_ETC2_EAC, GL_COMPRESSED_R11_EAC, GL_COMPRESSED_SIGNED_R11_EAC, GL_COMPRESSED_RG11_EAC, and GL_COMPRESSED_SIGNED_RG11_EAC are available only if the GL version is 4.3 or higher.