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GLFEEDBACKBUFFER(3G)			  OpenGL Manual 		     GLFEEDBACKBUFFER(3G)

NAME
       glFeedbackBuffer - controls feedback mode

C SPECIFICATION
       void glFeedbackBuffer(GLsizei size, GLenum type, GLfloat * buffer);

PARAMETERS
       size
	   Specifies the maximum number of values that can be written into buffer.

       type
	   Specifies a symbolic constant that describes the information that will be returned for
	   each vertex.  GL_2D, GL_3D, GL_3D_COLOR, GL_3D_COLOR_TEXTURE, and GL_4D_COLOR_TEXTURE
	   are accepted.

       buffer
	   Returns the feedback data.

DESCRIPTION
       The glFeedbackBuffer function controls feedback. Feedback, like selection, is a GL mode.
       The mode is selected by calling glRenderMode() with GL_FEEDBACK. When the GL is in
       feedback mode, no pixels are produced by rasterization. Instead, information about
       primitives that would have been rasterized is fed back to the application using the GL.

       glFeedbackBuffer has three arguments: buffer is a pointer to an array of floating-point
       values into which feedback information is placed.  size indicates the size of the array.
       type is a symbolic constant describing the information that is fed back for each vertex.
       glFeedbackBuffer must be issued before feedback mode is enabled (by calling glRenderMode()
       with argument GL_FEEDBACK). Setting GL_FEEDBACK without establishing the feedback buffer,
       or calling glFeedbackBuffer while the GL is in feedback mode, is an error.

       When glRenderMode() is called while in feedback mode, it returns the number of entries
       placed in the feedback array and resets the feedback array pointer to the base of the
       feedback buffer. The returned value never exceeds size. If the feedback data required more
       room than was available in buffer, glRenderMode() returns a negative value. To take the GL
       out of feedback mode, call glRenderMode() with a parameter value other than GL_FEEDBACK.

       While in feedback mode, each primitive, bitmap, or pixel rectangle that would be
       rasterized generates a block of values that are copied into the feedback array. If doing
       so would cause the number of entries to exceed the maximum, the block is partially written
       so as to fill the array (if there is any room left at all), and an overflow flag is set.
       Each block begins with a code indicating the primitive type, followed by values that
       describe the primitive's vertices and associated data. Entries are also written for
       bitmaps and pixel rectangles. Feedback occurs after polygon culling and glPolygonMode()
       interpretation of polygons has taken place, so polygons that are culled are not returned
       in the feedback buffer. It can also occur after polygons with more than three edges are
       broken up into triangles, if the GL implementation renders polygons by performing this
       decomposition.

       The glPassThrough() command can be used to insert a marker into the feedback buffer. See
       glPassThrough().

       Following is the grammar for the blocks of values written into the feedback buffer. Each
       primitive is indicated with a unique identifying value followed by some number of
       vertices. Polygon entries include an integer value indicating how many vertices follow. A
       vertex is fed back as some number of floating-point values, as determined by type. Colors
       are fed back as four values in RGBA mode and one value in color index mode.

       value is a floating-point number, and n is a floating-point integer giving the number of
       vertices in the polygon.  GL_POINT_TOKEN, GL_LINE_TOKEN, GL_LINE_RESET_TOKEN,
       GL_POLYGON_TOKEN, GL_BITMAP_TOKEN, GL_DRAW_PIXEL_TOKEN, GL_COPY_PIXEL_TOKEN and
       GL_PASS_THROUGH_TOKEN are symbolic floating-point constants.  GL_LINE_RESET_TOKEN is
       returned whenever the line stipple pattern is reset. The data returned as a vertex depends
       on the feedback type.

       The following table gives the correspondence between type and the number of values per
       vertex.	k is 1 in color index mode and 4 in RGBA mode.

       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+
       |			     |					   |				   |				     |					 |
       |			Type |			       Coordinates |			     Color |			     Texture |				 Total	 |
       |			     |					   |				   |				     |	 Number of Values		 |
       |			     |					   |				   |				     |					 |
       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+
       |GL_2D			     | x, y				   |				   |				     |		       2		 |
       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+
       |GL_3D			     | x, y, z				   |				   |				     |		       3		 |
       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+
       |GL_3D_COLOR		     | x, y, z				   |		   k		   |				     | 3				 |
       |			     |					   |				   |				     |				       + |
       |			     |					   |				   |				     |				       k |
       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+
       |GL_3D_COLOR_TEXTURE	     | x, y, z				   |		   k		   |		    4		     | 7				 |
       |			     |					   |				   |				     |				       + |
       |			     |					   |				   |				     |				       k |
       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+
       |GL_4D_COLOR_TEXTURE	     | x, y, z, w			   |		   k		   |		    4		     | 8				 |
       |			     |					   |				   |				     |				       + |
       |			     |					   |				   |				     |				       k |
       +-----------------------------+-------------------------------------+-------------------------------+---------------------------------+-----------------------------------+

       Feedback vertex coordinates are in window coordinates, except w, which is in clip
       coordinates. Feedback colors are lighted, if lighting is enabled. Feedback texture
       coordinates are generated, if texture coordinate generation is enabled. They are always
       transformed by the texture matrix.

NOTES
       glFeedbackBuffer, when used in a display list, is not compiled into the display list but
       is executed immediately.

       glFeedbackBuffer returns only the texture coordinate of texture unit GL_TEXTURE0.

ERRORS
       GL_INVALID_ENUM is generated if type is not an accepted value.

       GL_INVALID_VALUE is generated if size is negative.

       GL_INVALID_OPERATION is generated if glFeedbackBuffer is called while the render mode is
       GL_FEEDBACK, or if glRenderMode() is called with argument GL_FEEDBACK before
       glFeedbackBuffer is called at least once.

       GL_INVALID_OPERATION is generated if glFeedbackBuffer is executed between the execution of
       glBegin() and the corresponding execution of glEnd().

ASSOCIATED GETS
       glGet() with argument GL_RENDER_MODE

       glGet() with argument GL_FEEDBACK_BUFFER_POINTER

       glGet() with argument GL_FEEDBACK_BUFFER_SIZE

       glGet() with argument GL_FEEDBACK_BUFFER_TYPE

SEE ALSO
       glBegin(), glLineStipple(), glPassThrough(), glPolygonMode(), glRenderMode(),
       glSelectBuffer()

COPYRIGHT
       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI
       Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org				    06/10/2014			     GLFEEDBACKBUFFER(3G)
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