NAME

       glDrawElementsInstancedBaseInstance - draw multiple instances of a set of elements with
       offset applied to instanced attributes

C SPECIFICATION

       void glDrawElementsInstancedBaseInstance(GLenum mode, GLsizei count, GLenum type,
                                                const void * indices, GLsizei primcount,
                                                GLuitn baseinstance);

PARAMETERS

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

       count
           Specifies the number of elements to be rendered.

       type
           Specifies the type of the values in indices. Must be one of GL_UNSIGNED_BYTE,
           GL_UNSIGNED_SHORT, or GL_UNSIGNED_INT.

       indices
           Specifies a pointer to the location where the indices are stored.

       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

       glDrawElementsInstancedBaseInstance behaves identically to glDrawElements() except that
       primcount instances of the set 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.

       glDrawElementsInstancedBaseInstance has the same effect as:

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

NOTES

       glDrawElementsInstancedBaseInstance is available only if the GL version is 4.2 or greater.

       GL_LINE_STRIP_ADJACENCY, GL_LINES_ADJACENCY, GL_TRIANGLE_STRIP_ADJACENCY and
       GL_TRIANGLES_ADJACENCY are available only if the GL version is 3.2 or greater.

ERRORS

       GL_INVALID_ENUM is generated if mode is not one of GL_POINTS, GL_LINE_STRIP, GL_LINE_LOOP,
       GL_LINES, GL_TRIANGLE_STRIP, GL_TRIANGLE_FAN, or GL_TRIANGLES.

       GL_INVALID_VALUE is generated if count or primcount are negative.

       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_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

       glDrawElements(), glDrawArraysInstanced()

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