1GLFEEDBACKBUFFER(3G)             OpenGL Manual            GLFEEDBACKBUFFER(3G)
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NAME

6       glFeedbackBuffer - controls feedback mode
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C SPECIFICATION

9       void glFeedbackBuffer(GLsizei size, GLenum type, GLfloat * buffer);
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PARAMETERS

12       size
13           Specifies the maximum number of values that can be written into
14           buffer.
15
16       type
17           Specifies a symbolic constant that describes the information that
18           will be returned for each vertex.  GL_2D, GL_3D, GL_3D_COLOR,
19           GL_3D_COLOR_TEXTURE, and GL_4D_COLOR_TEXTURE are accepted.
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21       buffer
22           Returns the feedback data.
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DESCRIPTION

25       The glFeedbackBuffer function controls feedback. Feedback, like
26       selection, is a GL mode. The mode is selected by calling glRenderMode()
27       with GL_FEEDBACK. When the GL is in feedback mode, no pixels are
28       produced by rasterization. Instead, information about primitives that
29       would have been rasterized is fed back to the application using the GL.
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31       glFeedbackBuffer has three arguments: buffer is a pointer to an array
32       of floating-point values into which feedback information is placed.
33       size indicates the size of the array.  type is a symbolic constant
34       describing the information that is fed back for each vertex.
35       glFeedbackBuffer must be issued before feedback mode is enabled (by
36       calling glRenderMode() with argument GL_FEEDBACK). Setting GL_FEEDBACK
37       without establishing the feedback buffer, or calling glFeedbackBuffer
38       while the GL is in feedback mode, is an error.
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40       When glRenderMode() is called while in feedback mode, it returns the
41       number of entries placed in the feedback array and resets the feedback
42       array pointer to the base of the feedback buffer. The returned value
43       never exceeds size. If the feedback data required more room than was
44       available in buffer, glRenderMode() returns a negative value. To take
45       the GL out of feedback mode, call glRenderMode() with a parameter value
46       other than GL_FEEDBACK.
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48       While in feedback mode, each primitive, bitmap, or pixel rectangle that
49       would be rasterized generates a block of values that are copied into
50       the feedback array. If doing so would cause the number of entries to
51       exceed the maximum, the block is partially written so as to fill the
52       array (if there is any room left at all), and an overflow flag is set.
53       Each block begins with a code indicating the primitive type, followed
54       by values that describe the primitive's vertices and associated data.
55       Entries are also written for bitmaps and pixel rectangles. Feedback
56       occurs after polygon culling and glPolygonMode() interpretation of
57       polygons has taken place, so polygons that are culled are not returned
58       in the feedback buffer. It can also occur after polygons with more than
59       three edges are broken up into triangles, if the GL implementation
60       renders polygons by performing this decomposition.
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62       The glPassThrough() command can be used to insert a marker into the
63       feedback buffer. See glPassThrough().
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65       Following is the grammar for the blocks of values written into the
66       feedback buffer. Each primitive is indicated with a unique identifying
67       value followed by some number of vertices. Polygon entries include an
68       integer value indicating how many vertices follow. A vertex is fed back
69       as some number of floating-point values, as determined by type. Colors
70       are fed back as four values in RGBA mode and one value in color index
71       mode.
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73       value is a floating-point number, and n is a floating-point integer
74       giving the number of vertices in the polygon.  GL_POINT_TOKEN,
75       GL_LINE_TOKEN, GL_LINE_RESET_TOKEN, GL_POLYGON_TOKEN, GL_BITMAP_TOKEN,
76       GL_DRAW_PIXEL_TOKEN, GL_COPY_PIXEL_TOKEN and GL_PASS_THROUGH_TOKEN are
77       symbolic floating-point constants.  GL_LINE_RESET_TOKEN is returned
78       whenever the line stipple pattern is reset. The data returned as a
79       vertex depends on the feedback type.
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81       The following table gives the correspondence between type and the
82       number of values per vertex.  k is 1 in color index mode and 4 in RGBA
83       mode.
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85       ┌─────────────────────────────┬─────────────────────────────────────┬───────────────────────────────┬─────────────────────────────────┬───────────────────────────────────┐
86       │                             │                                     │                               │                                 │                                   │
87Type Coordinates Color Texture Total   
88       │                             │                                     │                               │                                 │   Number of                       
89       │                             │                                     │                               │                                 │   Values                          
90       │                             │                                     │                               │                                 │                                   │
91       ├─────────────────────────────┼─────────────────────────────────────┼───────────────────────────────┼─────────────────────────────────┼───────────────────────────────────┤
92GL_2D                        x, y                                │                               │                                 │                 2                 │
93       ├─────────────────────────────┼─────────────────────────────────────┼───────────────────────────────┼─────────────────────────────────┼───────────────────────────────────┤
94GL_3D                        x, y, z                             │                               │                                 │                 3                 │
95       ├─────────────────────────────┼─────────────────────────────────────┼───────────────────────────────┼─────────────────────────────────┼───────────────────────────────────┤
96GL_3D_COLOR                  x, y, z                             │               k               │                                 │ 3                                 │
97       │                             │                                     │                               │                                 │                                 + │
98       │                             │                                     │                               │                                 │                                 k │
99       ├─────────────────────────────┼─────────────────────────────────────┼───────────────────────────────┼─────────────────────────────────┼───────────────────────────────────┤
100GL_3D_COLOR_TEXTURE          x, y, z                             │               k               │                4                │ 7                                 │
101       │                             │                                     │                               │                                 │                                 + │
102       │                             │                                     │                               │                                 │                                 k │
103       ├─────────────────────────────┼─────────────────────────────────────┼───────────────────────────────┼─────────────────────────────────┼───────────────────────────────────┤
104GL_4D_COLOR_TEXTURE          x, y, z, w                          │               k               │                4                │ 8                                 │
105       │                             │                                     │                               │                                 │                                 + │
106       │                             │                                     │                               │                                 │                                 k │
107       └─────────────────────────────┴─────────────────────────────────────┴───────────────────────────────┴─────────────────────────────────┴───────────────────────────────────┘
108
109       Feedback vertex coordinates are in window coordinates, except w, which
110       is in clip coordinates. Feedback colors are lighted, if lighting is
111       enabled. Feedback texture coordinates are generated, if texture
112       coordinate generation is enabled. They are always transformed by the
113       texture matrix.
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NOTES

116       glFeedbackBuffer, when used in a display list, is not compiled into the
117       display list but is executed immediately.
118
119       glFeedbackBuffer returns only the texture coordinate of texture unit
120       GL_TEXTURE0.
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ERRORS

123       GL_INVALID_ENUM is generated if type is not an accepted value.
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125       GL_INVALID_VALUE is generated if size is negative.
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127       GL_INVALID_OPERATION is generated if glFeedbackBuffer is called while
128       the render mode is GL_FEEDBACK, or if glRenderMode() is called with
129       argument GL_FEEDBACK before glFeedbackBuffer is called at least once.
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131       GL_INVALID_OPERATION is generated if glFeedbackBuffer is executed
132       between the execution of glBegin() and the corresponding execution of
133       glEnd().
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ASSOCIATED GETS

136       glGet() with argument GL_RENDER_MODE
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138       glGet() with argument GL_FEEDBACK_BUFFER_POINTER
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140       glGet() with argument GL_FEEDBACK_BUFFER_SIZE
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142       glGet() with argument GL_FEEDBACK_BUFFER_TYPE
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SEE ALSO

145       glBegin(), glLineStipple(), glPassThrough(), glPolygonMode(),
146       glRenderMode(), glSelectBuffer()
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149       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
150       under the SGI Free Software B License. For details, see
151       http://oss.sgi.com/projects/FreeB/.
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AUTHORS

154       opengl.org
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158opengl.org                        07/13/2018              GLFEEDBACKBUFFER(3G)
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