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gluBuild2DMipmaps

Chapter 2

If the GL version is 1.1 or greater, gluBuild2DMipmaps then uses proxy textures (see

glTexImage1D) to determine whether there’s enough room for the requested texture in

the implementation. If not, width is halved (and halved again) until it ﬁts.

gluBuild2DMipmaps then uses proxy textures (see glTexImage2D) to determine if the

implementation can store the requested texture in texture memory. If not, both

dimensions are continually halved until it ﬁts.

Next, gluBuild2DMipmaps builds a series of images; it halves a copy of type (or a scaled

version of type, if necessary) along both dimensions until size 11 is reached. At each

level, each texel in the halved mipmap is an average of the corresponding four texels in

the larger mipmap. (In the case of rectangular images, halving the images repeatedly

eventually results in an n 1 or 1n conﬁguration. Here, two texels are averaged instead.)

glTexImage2D is called to load each of these images by level. If width and height are

both powers of 2 which ﬁt in the implementation, level 0 is a copy of data, and the

highest level is log

(max(width, height)). For example, if width is 64 and height is 16, the

following mipmaps 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.

See the glTexImage1D reference page for a description of the acceptable values for

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

type.

Notes

While you can’t query the maximum level directly, you can derive it indirectly by calling

glGetTexLevelParameter. First, query for the width and height actually used at level 0.

(The width and height may be unequal to width and height since proxy textures might

have shrunk or expanded them if width or height are not powers of 2 or if the

implementation only supports smaller textures.) The maximum level can then be

derived using the formula log

(max(width, height)).

Errors

• GLU_INVALID_VALUE is returned if width or height are negative.

• GLU_INVALID_ENUM is returned if format or type is not one of the accepted

values.

HP b2600 Reference Guide

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