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GLPIXELTRANSFORMPARAMETEREXT(3GL)	     GLPIXELTRANSFORMPARAMETEREXT(3GL)

NAME
       glPixelTransformParameter*EXT - set pixel transformation parameters

C Specification
       For Single-Value Attributes

       void	   glPixelTransformParameterfEXT(	 GLenum	       target,
					   GLenum			pname,
					   GLfloat param )
       void	   glPixelTransformParameteriEXT(	 GLenum	       target,
					      GLenum			pname,
					      GLint  param )

PARAMETERS
       target  The   target  pixel  transformation.  Must  be  GL_PIXEL_TRANS‐
	       FORM_2D_EXT.  pname The parameter to be set.  Must  be  one  of
	       GL_PIXEL_MIN_FILTER_EXT,	      GL_PIXEL_MAG_FILTER_EXT,	    or
	       GL_PIXEL_CUBIC_WEIGHT_EXT.  param The parameter value. If pname
	       is  GL_PIXEL_MAG_FILTER_EXT,  param  must be one of GL_NEAREST,
	       GL_LINEAR,  or  GL_CUBIC_EXT.  If  pname	 is  GL_PIXEL_MIN_FIL‐
	       TER_EXT,	  param	  must	 be   one  of  GL_NEAREST,  GL_LINEAR,
	       GL_CUBIC_EXT or GL_AVERAGE_EXT. If pname is any	of  the	 other
	       accepted	 values,  the  specified  parameter will be set to the
	       value of param.

C Specification
       For Multiple-Value Attributes

       void	  glPixelTransformParameterfvEXT(	 GLenum	       target,
					    GLenum			pname,
					    const GLfloat *params )

       void	  glPixelTransformParameterivEXT(	 GLenum	       target,
					    GLenum			pname,
					    const GLint *params )

PARAMETERS
       target	The  target  pixel  transformation.  Must  be  GL_PIXEL_TRANS‐
		FORM_2D_EXT.   pname  The  parameter to be set. Must be one of
		GL_PIXEL_MIN_FILTER_EXT,      GL_PIXEL_MAG_FILTER_EXT,	    or
		GL_PIXEL_CUBIC_WEIGHT_EXT.   params  The  parameter  value. If
		pname  is  GL_PIXEL_MAG_FILTER_EXT,  params  must  be  one  of
		GL_NEAREST,   GL_LINEAR,   or	GL_CUBIC_EXT.	If   pname  is
		GL_PIXEL_MIN_FILTER_EXT, params must  be  one  of  GL_NEAREST,
		GL_LINEAR,  GL_CUBIC_EXT or GL_AVERAGE_EXT. If pname is any of
		the other accepted values, the specified parameter will be set
		to the value of params.

DESCRIPTION
       glPixelTransformParameter*EXT is part of the EXT_pixel_transform exten‐
       sion, which adds image  scaling,	 rotation,  translation,  and  general
       affine  mapping	to  the	 pixel	rasterizer immediately after the pixel
       transfer path.

       The EXT_pixel_transform extension is always enabled.  It	 has  its  own
       matrix	stack,	 32  deep,  and	 is  identified	 with  GL_PIXEL_TRANS‐
       FORM_2D_EXT. To use this	 new  matrix  mode  use	 the  call:  glMatrix‐
       Mode(GL_PIXEL_TRANSFORM_2D_EXT).	 All OpenGL matrix operator calls will
       operate on this matrix stack, (ie.   glLoadIdentity(),  glLoadMatrix(),
       glMultMatrix(),	glPushMatrix(),	 glPopMatrix(), etc...) It is by using
       the current matrix of the GL_PIXEL_TRANSFORM_2D_EXT  matrix  mode  that
       the  pixel  transformation is defined. After each matrix operator call,
       the resulting matrix is then masked such that only  the	affine	compo‐
       nents, in the X and Y dimensions, are kept. See below:

       Given Matrix P:		  P masked to preserve affine components:

	    | m0 m4  m8	  m12|	       | m0 m4	0 m12|
       P =  | m1 m5  m9	  m13|	  P =  | m1 m5	0 m13|
	    | m2 m6  m10  m14|	       | 0   0	1   0|
	    | m3  m7 m11  m15|	       | 0   0	0   1|

       The function void glPixelZoom( float zx, float zy ) ; will set the cur‐
       rent pixel transformation matrix (the current top of the	 pixel	trans‐
       formation matrix stack) to the scaling matrix:

	    |zoomX	0	0    0|
	    |  0      zoomY	0    1|
	    |  0	0	1    0|
	    |  0	0	0    1|

       The  transformation  is	applied	 to  the  image	 in terms of the input
       image's coordinates, where the lower left corner of the image has coor‐
       dinates	of  (0,0).  After  the	transformation is applied, the current
       raster position is then added to the X, Y coordinates of the  resulting
       output  image pixel coordinates, effectively translating the image pix‐
       els before displaying to the window. If the current rastor position  is
       not valid, then no output is generated.

NOTES
       GL_PIXEL_MIN_FILTER_EXT	defines the resampling technique that is to be
       applied	if  the	 image	 is   minified	 by   the   scaling   factors.
       GL_PIXEL_MAG_FILTER_EXT establishes the resampling technique that is to
       be used after  the  other  image	 transformation	 operators  have  been
       applied	  if	the    image	is    to    have    been    magnified.
       GL_PIXEL_CUBIC_WEIGHT_EXT defines the cubic weighting coefficient  that
       is to be used whenever the resampling technique is set to GL_CUBIC_EXT.

       Pixel  transformation  is  defined  for	pixel  rectangles that contain
       GL_COLOR_INDEX, GL_LUMINANCE, GL_LUMINANCE_ALPHA, GL_RGB,  GL_RGBA,  or
       GL_ABGR_EXT components or depth components in pixel rastorization.

       Since  multiple	input  pixels can be mapped into a single output pixel
       (minification of input image), or since output pixels  might  not  have
       any  input  pixels  mapped to them (magnification of input image), some
       method of resampling is required. If the resampling method is  GL_NEAR‐
       EST,  each  output  pixel  will have the value of the input pixel whose
       transformed coordinate value is nearest (in Manhattan distance). If the
       resampling  method  is  GL_LINEAR,  each output pixel will have a value
       that is the weighted average of the four input pixels whose transformed
       coordinate values are nearest.

       If the resampling method is GL_CUBIC_EXT, each output pixel will have a
       value that is affected by the 16 input pixels whose transformed coordi‐
       nate  values are nearest. The 16 input pixels will be used to perform a
       cubic spline interpolation to determine the value of the output	pixel.
       The  cubic  weight  factor is a floating point value that is applied to
       the cubic interpolation in the manner described in "Digital Image Warp‐
       ing"   by   George   Wolberg   (IEEE   Computer	 Society  Press,  ISBN
       0-8186-8944-7). Visually pleasing cubic weighting values are  typically
       in  the	range [-1,0]. The values -1.0 and -0.5 are most commonly used.
       For the purpose of performing bicubic  interpolation  along  the	 outer
       edge  of the pixel rectangle, the outermost one pixel edge of the pixel
       rectangle is duplicated prior to performing the interpolation along the
       edges.

       If  the	resampling  method is GL_AVERAGE_EXT, the values of all of the
       input pixels that contribute to the final output pixel will be averaged
       to  determine the final output pixel value. That is, an output pixel is
       backward mapped into the input pixel rectangle, then the nearest neigh‐
       bor  resampling method determines the address of the center input pixel
       from which input pixels will be averaged. All pixels in the input  that
       forward	map  into the same location in the output pixel rectangle will
       be added together and divided by the total number of input pixels which
       contribute the same output pixel. For example, if the output pixel rec‐
       tangle is 1/3 the size of the input pixel rectangle, then a total of  9
       pixels would be read from the input pixel rectangle, averaged, and then
       the new single value will be written into the output pixel rectangle.

DEFAULTS
       The  default  current  matrix  for  the	matrix	mode   GL_PIXEL_TRANS‐
       FORM_2D_EXT  is	the  identity  matrix. While the current matrix is the
       identity matrix for the matrix mode GL_PIXEL_TRANSFORM_2D_EXT, no pixel
       transform operation will be performed. Only when this current matrix is
       not an identity matrix will the pixel  tranformation  take  place.  The
       default value for the cubic weighting factor is -1.0. The default mini‐
       fication and magnification filters are GL_NEAREST.

ERRORS
       GL_INVALID_ENUM is generated if target or pname is  not	an  acceptable
       value. GL_INVALID_ENUM is generated if pname is GL_PIXEL_MAG_FILTER_EXT
       and the specified parameter value is not one of GL_NEAREST,  GL_LINEAR,
       or   GL_CUBIC_EXT.   GL_INVALID_ENUM   is   generated   if   pname   is
       GL_PIXEL_MIN_FILTER_EXT and the specified parameter value is not one of
       GL_NEAREST, GL_LINEAR, GL_CUBIC_EXT, or GL_AVERAGE_EXT.

SEE ALSO
       glGetPixelTransformParameterEXT

				  24 Sept 97 GLPIXELTRANSFORMPARAMETEREXT(3GL)
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