Glu.Build2DMipmaps (gb.opengl.glu)

Parameters

Image

Specifies the Image from which the mipmaps will be generated.

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Description

Glu.Build2DMipmaps 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.

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

Initially, the width and height of the Image are checked to see if they are a power of 2. If not, a copy of the Image, 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 of the Image is exactly between powers of 2, then the copy will be scale upwards.)

Then, proxy textures (see Gl.TexImage2D) 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 Gl.GetIntegerv with the argument Glu.MAX_TEXTURE_SIZE.)

Next, a series of mipmap levels is built by decimating a copy of the Image in half along both dimensions until size $1\times 1$ 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 $\mathit{N}\times 1$ or $1\times \mathit{N}$ configuration. Here, two texels are averaged instead.)

Gl.TexImage2D is called to load each of these mipmap levels. Level 0 is a copy of data. The highest level is ${\mathit{log}}_2\left(\mathit{max}\left(\mathit{width},\mathit{height}\right)\right)$. 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: $64\times 16$, $32\times 8$, $16\times 4$, $8\times 2$, $4\times 1$, $2\times 1$, and $1\times 1$ These correspond to levels 0 through 6, respectively.

See the Gl.TexImage1D reference page for a description of the acceptable values for format parameter. See the Gl.DrawPixels reference page for a description of the acceptable values for type parameter.

Notes

Note that there is no direct way of querying the maximum level. This can be derived indirectly via Gl.GetTexLevelParameter. 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 ${\mathit{log}}_2\left(\mathit{max}\left(\mathit{width},\mathit{height}\right)\right)$.

Formats Glu.BGR, and Glu.BGRA, and types Glu.UNSIGNED_BYTE_3_3_2, Glu.UNSIGNED_BYTE_2_3_3_REV, Glu.UNSIGNED_SHORT_5_6_5, Glu.UNSIGNED_SHORT_5_6_5_REV, Glu.UNSIGNED_SHORT_4_4_4_4, Glu.UNSIGNED_SHORT_4_4_4_4_REV, Glu.UNSIGNED_SHORT_5_5_5_1, Glu.UNSIGNED_SHORT_1_5_5_5_REV, Glu.UNSIGNED_INT_8_8_8_8, Glu.UNSIGNED_INT_8_8_8_8_REV, Glu.UNSIGNED_INT_10_10_10_2, and Glu.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.

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 Glu.UNSIGNED_BYTE_3_3_2 or Glu.UNSIGNED_BYTE_2_3_3_REV and format is not Glu.RGB.

Glu.INVALID_OPERATION is returned if type is Glu.UNSIGNED_SHORT_5_6_5 or Glu.UNSIGNED_SHORT_5_6_5_REV and format is not Glu.RGB.

Glu.INVALID_OPERATION is returned if type is Glu.UNSIGNED_SHORT_4_4_4_4 or Glu.UNSIGNED_SHORT_4_4_4_4_REV and format is neither Glu.RGBA nor Glu.BGRA.

Glu.INVALID_OPERATION is returned if type is Glu.UNSIGNED_SHORT_5_5_5_1 or Glu.UNSIGNED_SHORT_1_5_5_5_REV and format is neither Glu.RGBA nor Glu.BGRA.

Glu.INVALID_OPERATION is returned if type is Glu.UNSIGNED_INT_8_8_8_8 or Glu.UNSIGNED_INT_8_8_8_8_REV and format is neither Glu.RGBA nor Glu.BGRA.

Glu.INVALID_OPERATION is returned if type is Glu.UNSIGNED_INT_10_10_10_2 or Glu.UNSIGNED_INT_2_10_10_10_REV and format is neither Glu.RGBA nor Glu.BGRA.

See also

Glu.Build1DMipmapLevels,

• Glu.Build1DMipmaps,

Glu.Build2DMipmapLevels, Glu.Build3DMipmapLevels, Glu.Build3DMipmaps, Glu.ErrorString,

• Gl.DrawPixels,

Gl.GetTexImage, Gl.GetTexLevelParameter,

• Gl.TexImage1D,

• Gl.TexImage2D,

Gl.TexImage3D

See original documentation on OpenGL website