GLUBUILD2DMIPMAPS(3G)

✨ NAME ✨

gluBuild2DMipmaps — builds a two-dimensional mipmap 🦋 and yes bestie, we are in the GLU manual, section 3G, and this one is lowkey iconic.

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🎀 C SPECIFICATION 🎀

GLint gluBuild2DMipmaps( GLenum target,
                         GLint internalFormat,
                         GLsizei width,
                         GLsizei height,
                         GLenum format,
                         GLenum type,
                         const void *data )

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💅 PARAMETERS 💅

• target — the target texture, periodt. It must be GL_TEXTURE_2D. That's the vibe check and it does not negotiate. 💀
• internalFormat — requests the internal storage of the texture image. Okay so here's the tea ☕: the most current version of the SGI implementation of GLU does not check this value for validity before passing it on to the underlying OpenGL implementation. A value that is not accepted by the OpenGL implementation will lead to an OpenGL error. The benefit of not checking this value at the GLU level is that OpenGL extensions can add new internal texture formats without requiring a revision of the GLU implementation. Older implementations of GLU do check this value and raise a GLU error if it is not 1, 2, 3, or 4, or one of the following symbolic constants: GL_ALPHA, GL_ALPHA4, GL_ALPHA8, GL_ALPHA12, GL_ALPHA16, GL_LUMINANCE, GL_LUMINANCE4, GL_LUMINANCE8, GL_LUMINANCE12, GL_LUMINANCE16, GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4, GL_LUMINANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8, GL_LUMINANCE12_ALPHA4, GL_LUMINANCE12_ALPHA12, GL_LUMINANCE16_ALPHA16, GL_INTENSITY, GL_INTENSITY4, GL_INTENSITY8, GL_INTENSITY12, GL_INTENSITY16, GL_RGB, GL_R3_G3_B2, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10, GL_RGB12, GL_RGB16, GL_RGBA, GL_RGBA2, GL_RGBA4, GL_RGB5_A1, GL_RGBA8, GL_RGB10_A2, GL_RGBA12 or GL_RGBA16. Long list? Yeah. But every single one of them ate. 💖
• width, height — in pixels, the width and the height, respectively, of the texture image. 📐
• format — specifies the _____ of the pixel data. Not me leaving a blank there — the original literally has a gap right at that spot 💀 and I'm not about to invent facts, bestie. What I can tell you is it must be one of GL_COLOR_INDEX, GL_DEPTH_COMPONENT, GL_RED, GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB, GL_RGBA, GL_BGR, GL_BGRA, GL_LUMINANCE, or GL_LUMINANCE_ALPHA.
• type — specifies the data type for data. Must be one of GL_UNSIGNED_BYTE, GL_BYTE, GL_BITMAP, GL_UNSIGNED_SHORT, GL_SHORT, GL_UNSIGNED_INT, GL_INT, GL_FLOAT, GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, or GL_UNSIGNED_INT_2_10_10_10_REV. ✨
• data — a pointer to the image data in memory. That's it, that's the whole job. 🫶

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🌸 DESCRIPTION 🌸

gluBuild2DMipmaps builds a series of prefiltered two-dimensional texture maps of decreasing resolutions called a mipmap. This is used for the antialiasing of texture-mapped primitives. Basically it's the glow-up pipeline for your textures. ✨

A return value of zero indicates success, otherwise a GLU error code is returned (see gluErrorString).

Initially, the width and height of data are checked to see if they are a power of 2. If not, a copy of data (not data), is scaled up or down to the nearest power of 2. This copy will be used for subsequent mipmapping operations described below. (If width or height is exactly between powers of 2, then the copy of data will scale upwards.) For example, if width is 57 and height is 23 then a copy of data will scale up to 64 in width and down to 16 in depth, before mipmapping takes place. The way that 57 and 23 get rounded is genuinely a whole personality trait. 😭

Then, proxy textures (see glTexImage2D) are used to determine if the implementation can fit the requested texture. If not, both dimensions are continually halved until it fits. (If the OpenGL version is ≤ 1.0, both maximum texture dimensions are clamped to the value returned by glGetIntegerv with the argument GL_MAX_TEXTURE_SIZE.)

Next, a series of mipmap levels is built by decimating a copy of data in half along both dimensions until size 1×1 is reached. At each level, each texel in the halved mipmap level is an average of the corresponding four texels in the larger mipmap level. (In the case of rectangular images, the decimation will ultimately reach an N×1 or 1×N configuration. Here, two texels are averaged instead.) Shrinking down to 1×1 and still serving looks? Main character energy, honestly. 👑

glTexImage2D is called to load each of these mipmap levels. Level 0 is a copy of data. The highest level is log2(max(width,height)). For example, if width is 64 and height is 16 and the implementation can store a texture of this size, the following mipmap levels are built: 64×16, 32×8, 16×4, 8×2, 4×1, 2×1 and 1×1. These correspond to levels 0 through 6, respectively. Look at that little staircase of levels, obsessed. 🪜

See the glTexImage1D reference page for a description of the acceptable values for format parameter. See the glDrawPixels reference page for a description of the acceptable values for type parameter.

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🧚 NOTES 🧚

Note that there is no direct way of querying the maximum level. This can be derived indirectly via glGetTexLevelParameter. First, query for the width and height actually used at level 0. (The width and height may not be equal to width and height respectively since proxy textures might have scaled them to fit the implementation.) Then the maximum level can be derived from the formula log2(max(width,height)). Sneaky little derivation, but it works. 💅

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🧚 NOTES 🧚

Formats GL_BGR, and GL_BGRA, and types GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, and GL_UNSIGNED_INT_2_10_10_10_REV are only available if the GL version is 1.2 or greater and if the GLU version is 1.3 or greater. Version gate, bestie — check your GL and your GLU. 🚪

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💀 ERRORS 💀

• GLU_INVALID_VALUE is returned if width, or height is < 1.
• GLU_INVALID_ENUM is returned if internalFormat, format, or type is not legal.
• GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_BYTE_3_3_2 or GL_UNSIGNED_BYTE_2_3_3_REV and format is not GL_RGB.
• GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_6_5 or GL_UNSIGNED_SHORT_5_6_5_REV and format is not GL_RGB.
• GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_4_4_4_4 or GL_UNSIGNED_SHORT_4_4_4_4_REV and format is neither GL_RGBA nor GL_BGRA.
• GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_SHORT_5_5_5_1 or GL_UNSIGNED_SHORT_1_5_5_5_REV and format is neither GL_RGBA nor GL_BGRA.
• GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_INT_8_8_8_8 or GL_UNSIGNED_INT_8_8_8_8_REV and format is neither GL_RGBA nor GL_BGRA.
• GLU_INVALID_OPERATION is returned if type is GL_UNSIGNED_INT_10_10_10_2 or GL_UNSIGNED_INT_2_10_10_10_REV and format is neither GL_RGBA nor GL_BGRA.

Mismatched type and format combos get you a GLU_INVALID_OPERATION, no cap. Read the pairs, bestie, they're matching outfits and you can't mix them. 🙈

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👑 SEE ALSO 👑

glDrawPixels(3G), glTexImage1D(3G), glTexImage2D(3G), glTexImage3D(3G), gluBuild1DMipmaps(3G), gluBuild3DMipmaps(3G), gluErrorString(3G), glGetTexImage(3G), glGetTexLevelParameter(3G), gluBuild1DMipmapLevels(3G), gluBuild2DMipmapLevels(3G), gluBuild3DMipmapLevels(3G)

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And that's the whole page, mwah 💋 — you just read GLUBUILD2DMIPMAPS(3G), the GLU manual section 3G entry, top to bottom, and honestly? Slay. Go build some mipmaps, bestie. 🌈🎀💖