gluBuild2DMipmaps(3G)	       OpenGL Reference		 gluBuild2DMipmaps(3G)



NAME
     gluBuild2DMipmaps - builds	2-D mipmaps


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


PARAMETERS
     target	Specifies the target texture.  Must be GL_TEXTURE_2D.

     component	Specifies the number of	color components in the	texture.  Must
		be 1, 2, 3, or 4 or one	of the following symbolic constants:
		GL_ALPHA, GL_INTENSITY_EXT, GL_LUMINANCE, GL_LUMINANCE_ALPHA,
		GL_RGB,	GL_RGBA.

     width, height
		Specifies the width and	height,	respectively, in pixels	of the
		texture	image.

     format	Specifies the format of	the pixel data.	 Must be one of:
		GL_COLOR_INDEX,	GL_RED,	GL_GREEN, GL_BLUE, GL_ALPHA, GL_RGB,
		GL_RGBA, GL_LUMINANCE, GL_LUMINANCE_ALPHA and GL_ABGR_EXT.

     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_EXT, GL_UNSIGNED_SHORT_4_4_4_4_EXT,
		GL_UNSIGNED_SHORT_5_5_5_1_EXT, GL_UNSIGNED_INT_8_8_8_8_EXT,
		and GL_UNSIGNED_INT_10_10_10_2_EXT.

     data	Specifies a pointer to the image data in memory.



DESCRIPTION
     gluBuild2DMipmaps builds a	series of prefiltered 2-D texture maps of
     decreasing	resolutions called mipmaps. These are used for the
     antialiasing of texture mapped primitives.

     A return value of 0 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 two. If not, a copy of data is scaled up or down to the nearest
     power of two. This	copy will be used for subsequent mipmapping operations



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gluBuild2DMipmaps(3G)	       OpenGL Reference		 gluBuild2DMipmaps(3G)



     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 and down to 16,
     respectively, before mipmapping takes place.

     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.

     Next, a series of mipmaps is built	by decimating a	copy of	data in	half
     along both	dimensions until size 1x1 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, the decimation
     will ultimately reach an N	x 1 or 1 x N configuration. Here, two texels
     are averaged instead.)

     glTexImage2D is called to load each of these mipmaps by level.  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 mipmaps are built: 64x16, 32x8,
     16x4, 8x2,	4x1, 2x1 and 1x1. These	correspond to levels 0 through 6,
     respectively.

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

NOTES
     Note that there is	no direct way of querying the maximum level. This can
     be	queried	indirectly via glGetTexLevelParameter. First, query for	the
     width & height actually used at level 0. (The width & height may be <=
     width & height respectively since proxy textures might have shrunk	them
     to	fit the	implementation.) Then the maximum level	can be derived from
     the formula log2(max(width,height)).

ERRORS
     GLU_INVALID_VALUE is returned if width or height are < 1.

     GLU_INVALID_ENUM is returned if format or type are	not legal.

     GLU_INVALID_ENUM is returned if type is GL_UNSIGNED_BYTE_3_3_2_EXT	and
     format is not GL_RGB.

     GLU_INVALID_ENUM is returned if type is GL_UNSIGNED_SHORT_4_4_4_4_EXT and
     format is neither GL_RGBA nor GL_ABGR_EXT.

     GLU_INVALID_ENUM is returned if type is GL_UNSIGNED_SHORT_5_5_5_1_EXT and
     format is neither GL_RGBA nor GL_ABGR_EXT.






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gluBuild2DMipmaps(3G)	       OpenGL Reference		 gluBuild2DMipmaps(3G)



     GLU_INVALID_ENUM is returned if type is GL_UNSIGNED_INT_8_8_8_8_EXT and
     format is neither GL_RGBA nor GL_ABGR_EXT.

     GLU_INVALID_ENUM is returned if type is GL_UNSIGNED_INT_10_10_10_2_EXT
     and format	is neither GL_RGBA nor GL_ABGR_EXT.

BUGS
     Passing GL_STENCIL_INDEX or GL_DEPTH_COMPONENT as format will incorrectly
     return 0 and set the error	code to	GL_INVALID_ENUM. It should return
     GLU_INVALID_ENUM and not set an error code.

SEE ALSO
     glDrawPixels, glTexImage1D, glTexImage2D, gluBuild1DMipmaps,
     gluErrorString, glGetTexImage, glGetTexLevelParameter.









































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