glTransformFeedbackVaryings

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Specify values to record in transform feedback buffers.

C Specification[edit]

void glTransformFeedbackVaryings( GLuint program, GLsizei count, const char ** varyings, GLenum bufferMode );


Parameters[edit]

program - The name of the target program object.
count - The number of varying variables used for transform feedback.
varyings - An array of count zero-terminated strings specifying the names of the varying variables to use for transform feedback.
bufferMode - Identifies the mode used to capture the varying variables when transform feedback is active. bufferMode must be GL_INTERLEAVED_ATTRIBS or GL_SEPARATE_ATTRIBS .


Description[edit]

The names of the vertex or geometry shader outputs to be recorded in transform feedback mode are specified using glTransformFeedbackVaryings . When a geometry shader is active, transform feedback records the values of selected geometry shader output variables from the emitted vertices. Otherwise, the values of the selected vertex shader outputs are recorded.

The state set by glTranformFeedbackVaryings is stored and takes effect next time glLinkProgram is called on program . When glLinkProgram is called, program is linked so that the values of the specified varying variables for the vertices of each primitive generated by the GL are written to a single buffer object if bufferMode is GL_INTERLEAVED_ATTRIBS or multiple buffer objects if bufferMode is GL_SEPARATE_ATTRIBS .

 glTransformFeedbackVaryings can also special identifiers if bufferMode is GL_INTERLEAVED_ATTRIBS :

gl_NextBufferSubsequent variables in varyings will be assigned to the next buffer binding point.

gl_SkipComponents#Where # may be 1, 2, 3, or 4. The variable is treated as having this number of components, but the contents of the memory are preserved under feedback operations.

In addition to the errors generated by glTransformFeedbackVaryings , the program program will fail to link if:*The count specified by glTransformFeedbackVaryings is non-zero, but the program object has no vertex or geometry shader.

  • Any variable name specified in the varyings array is not declared as an output in the vertex shader (or the geometry shader, if active), or is not one of the special identifiers listed above.
  • Special identifiers appear in a varyings array where bufferMode is not GL_INTERLEAVED_ATTRIBS .
  • Any two entries in the varyings array, which are not one of the special varyings above, specify the same varying variable.
  • Discounting any special identifiers, the total number of components to capture in any varying variable in varyings is greater than the constant GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS and the buffer mode is GL_SEPARATE_ATTRIBS .
  • The total number of components to capture is greater than the constant GL_MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS and the buffer mode is GL_INTERLEAVED_ATTRIBS .



Notes[edit]

 glGetTransformFeedbackVarying is available only if the GL version is 3.0 or greater.


Errors[edit]

 GL_INVALID_VALUE is generated if program is not the name of a program object.

 GL_INVALID_VALUE is generated if bufferMode is GL_SEPARATE_ATTRIBS and count is greater than the implementation-dependent limit GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_ATTRIBS .


Associated Gets[edit]

 glGetTransformFeedbackVarying 


Version Support[edit]

 glTransformFeedbackVaryings  3.0+

See Also[edit]

 glBeginTransformFeedback , glEndTransformFeedback , glGetTransformFeedbackVarying 


Copyright[edit]

Copyright© 2010-2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.