specify the primitive restart index
Specifies the value to be interpreted as the primitive restart index.
glPrimitiveRestartIndex specifies a vertex array element that is treated specially when primitive restarting is enabled. This is known as the primitive restart index.
When one of the Draw* commands transfers a set of generic attribute array elements to the GL, if the index within the vertex arrays corresponding to that set is equal to the primitive restart index, then the GL does not process those elements as a vertex. Instead, it is as if the drawing command ended with the immediately preceding transfer, and another drawing command is immediately started with the same parameters, but only transferring the immediately following element through the end of the originally specified elements.
glPrimitiveRestartIndex is available only if the GL version is 3.1 or greater.
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