GLCOMPRESSEDTEXIMAGE(3G)

📦
version 1.1 · 7 versions
, in centos-stream 9

💅 NAME 💅

glCompressedTexImage1D — specify a one-dimensional texture image in a compressed format. And yes bestie, that (3G) at the top of the page is just the manual section, it's not like a Lite version of the function 💀 this is the whole thing.

✨ C SPECIFICATION ✨

void glCompressedTexImage1D(GLenum target, GLint level,
                            GLenum internalformat, GLsizei width,
                            GLint border, GLsizei imageSize,
                            const GLvoid * data);

🎀 PARAMETERS 🎀

  • target — which texture slot we're loading into. It's gotta be either GL_TEXTURE_1D or GL_PROXY_TEXTURE_1D. That's it, those are the only two, no third option.
  • level — the level-of-detail number, aka which mipmap step we're on. 0 is the base image level, and level n is the nth mipmap reduction image. So level 0 is main character energy and everything above is its little sisters.
  • internalformat — the format of the compressed image data stored at address data. Lowkey the whole personality of this call.
  • width — the width of the texture image. Every implementation supports texture images that are at least 64 texels wide. And the height of the 1D texture image is 1 — that's the whole point of 1D, it's a single row, slay.
  • border — this value must be 0. Like, it's not a suggestion. It's 0.
  • imageSize — how many unsigned bytes of image data you're handing over, starting at the address specified by data.
  • data — pointer to the compressed image data in memory. The goods. 🙈

🦋 DESCRIPTION 🦋

Texturing allows elements of an image array to be read by shaders. That's the vibe.

glCompressedTexImage1D loads a previously defined, and retrieved, compressed one-dimensional texture image if target is GL_TEXTURE_1D (see glTexImage1D()).

If target is GL_PROXY_TEXTURE_1D, literally nothing gets read from data, but all of the texture image state is recalculated, checked for consistency, and checked against the implementation's capabilities. And if the implementation can't 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()). No drama, no error code, just vibes and zeroes. To query for an entire mipmap array, use an image array level greater than or equal to 1.

internalformat must be an extension-specified compressed-texture format. When a texture is loaded with glTexImage1D() using a generic compressed texture format (e.g., GL_COMPRESSED_RGB) the GL selects from one of its extensions supporting compressed textures. So in order to load the compressed texture image using glCompressedTexImage1D, you query the compressed texture image's size and format using glGetTexLevelParameter(). Ask the GL what it picked, then feed it back. It's giving respectful communication honestly 🫶

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. Not a pointer, an offset. Forever screaming about this distinction.

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 glTexImage1D(). 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. And all parameters must be consistent with the compressed format to produce the desired results — it's a whole ecosystem, they've got to be in agreement.

When selecting a sub-rectangle from a compressed image, two things to know:

  • the value of GL_UNPACK_SKIP_PIXELS must be a multiple of bw

imageSize must be equal to:

b s × width b w

(That's exactly how it's printed, bestie — the subscripts didn't survive the trip. It's bs times width over bw energy, but I'm not out here rewriting the page for them. 💀)

🔥 ERRORS 🔥

  • GL_INVALID_ENUM is generated if internalformat is not a supported specific compressed internal formats, or is 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. (Told you.)
  • 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. Read that again. Abnormal program termination. Your whole app can just ✨leave✨. Encode your data correctly, please and thank you 😭

👑 ASSOCIATED GETS 👑

  • glGetCompressedTexImage()
  • glGet() with argument GL_TEXTURE_COMPRESSED
  • glGet() with argument GL_NUM_COMPRESSED_TEXTURE_FORMATS
  • glGet() with argument GL_COMPRESSED_TEXTURE_FORMATS
  • glGet() with argument GL_PIXEL_UNPACK_BUFFER_BINDING
  • glGetTexLevelParameter() with arguments GL_TEXTURE_INTERNAL_FORMAT and GL_TEXTURE_COMPRESSED_IMAGE_SIZE

🌈 VERSION SUPPORT 🌈

The original page has a whole grid here. Here's the entire tea, no cap:

  • Function / feature name: glCompressedTexImage1D
  • OpenGL versions: 2.0, 2.1, 3.0, 3.1, 3.2, 3.3, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5
  • Support in every single one of them: ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔

Not me being obsessed with a function that's been iconic since day one. Twelve for twelve, periodt. 👑

🌸 SEE ALSO 🌸

  • glActiveTexture()
  • glCompressedTexImage2D()
  • glCompressedTexImage3D()
  • glCompressedTexSubImage1D()
  • glCompressedTexSubImage2D()
  • glCompressedTexSubImage3D()
  • glCopyTexImage1D()
  • glCopyTexImage2D()
  • glCopyTexSubImage1D()
  • glCopyTexSubImage2D()
  • glCopyTexSubImage3D()
  • glPixelStore()
  • glTexImage2D()
  • glTexImage3D()
  • glTexSubImage1D()
  • glTexSubImage2D()
  • glTexSubImage3D()
  • glTexParameter()

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2011-2014 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

⭐ COPYRIGHT (yes, again, the page really does this) ⭐

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2011-2014 Khronos Group

And that's the whole page, bestie 🫶 The source line was literally [FIXME: source], dated 08/09/2021 — so whoever shipped this never filled in where it came from, and honestly? Relatable. Go forth and compress your textures. 💖✨🎀

📦 where this page comes from