Contains the index of the current vertex.
gl_VertexIDis a vertex language input variable that holds an integer index for the vertex. The index is implicitly generated byglDrawArraysand other commands that do not reference the content of the
GL_ELEMENT_ARRAY_BUFFER , or explicitly generated from the content of the
GL_ELEMENT_ARRAY_BUFFER by commands such as
glDrawElements . For
glDrawElements forms that take a
basevertex ,gl_VertexIDwill have this value added to the index from the buffer.
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