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GLDRAWARRAYSINSTANCE(3G)	 OpenGL Manual	      GLDRAWARRAYSINSTANCE(3G)

NAME
       glDrawArraysInstancedBaseInstance - draw multiple instances of a range
       of elements with offset applied to instanced attributes

C SPECIFICATION
       void glDrawArraysInstancedBaseInstance(GLenum mode, GLint first,
					      GLsizei count,
					      GLsizei primcount,
					      GLuint baseinstance);

PARAMETERS
       mode
	   Specifies what kind of primitives to render. Symbolic constants
	   GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP, GL_LINES,
	   GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, GL_TRIANGLESGL_LINES_ADJACENCY,
	   GL_LINE_STRIP_ADJACENCY, GL_TRIANGLES_ADJACENCY,
	   GL_TRIANGLE_STRIP_ADJACENCY and GL_PATCHES are accepted.

       first
	   Specifies the starting index in the enabled arrays.

       count
	   Specifies the number of indices to be rendered.

       primcount
	   Specifies the number of instances of the specified range of indices
	   to be rendered.

       baseinstance
	   Specifies the base instance for use in fetching instanced vertex
	   attributes.

DESCRIPTION
       glDrawArraysInstancedBaseInstance behaves identically to glDrawArrays()
       except that primcount instances of the range of elements are executed
       and the value of the internal counter instanceID advances for each
       iteration.  instanceID is an internal 32-bit integer counter that may
       be read by a vertex shader as gl_InstanceID.

       glDrawArraysInstancedBaseInstance has the same effect as:

	       if ( mode or count is invalid )
		   generate appropriate error
	       else {
		   for (int i = 0; i < primcount ; i++) {
		       instanceID = i;
		       glDrawArrays(mode, first, count);
		   }
		   instanceID = 0;
	       }

       Specific vertex attributes may be classified as instanced through the
       use of glVertexAttribDivisor(). Instanced vertex attributes supply
       per-instance vertex data to the vertex shader. The index of the vertex
       fetched from the enabled instanced vertex attribute arrays is
       calculated as: gl _ InstanceID divisor + baseInstance. Note that
       baseinstance does not affect the shader-visible value of gl_InstanceID.

ERRORS
       GL_INVALID_ENUM is generated if mode is not one of the accepted values.

       GL_INVALID_OPERATION is generated if a geometry shader is active and
       mode is incompatible with the input primitive type of the geometry
       shader in the currently installed program object.

       GL_INVALID_VALUE is generated if count or primcount are negative.

       GL_INVALID_OPERATION is generated if a non-zero buffer object name is
       bound to an enabled array and the buffer object's data store is
       currently mapped.

SEE ALSO
       glDrawArrays(), glDrawElementsInstanced()

COPYRIGHT
       Copyright © 2011 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/.

AUTHORS
       opengl.org

opengl.org			  04/29/2014	      GLDRAWARRAYSINSTANCE(3G)

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