Define: glTransformFeedback()

GLAPI/glTransformFeedbackVaryings

glTransformFeedbackVaryings: specify values to record in transform feedback buffers..

Function Definition

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

program

The name of the target program object.

count

The number of varying variables used for transform feedback.

varyings

An array of count​ null-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

The names of the final active Vertex Processing shader stage outputs to be recorded in transform feedback mode are specified using glTransformFeedbackVaryings.

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.

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 Processing shader stage;

• any variable name specified in the varyings​ array is not one of the special varyings named below, and is not declared as an output in the final active Vertex Processing;

• any two entries in the varyings​ array specify the same varying variable;

• 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; or

• the set of varyings to capture to any single binding point includes varyings from more than one vertex stream.

Varyings can be named in the varyings​ array that do not specify an actual varying to capture. These are instead control values that affect the way the values are captured. These control values can only be used with GL_INTERLEAVED_ATTRIBS. The control values and their meaning are:

gl_NextBuffer

Subsequent captured varyings will be stored in the next transform feedback binding point.

gl_SkipComponents#

This specifies that there will be an empty place in the captured data, so the feedback operation will skip writing up to # components. # is a number 1-4. Memory skipped in this way will not be modified. These components still count towards the limitations on transform feedback components to be captured in a single buffer.

Notes

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

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