glDrawElementsInstancedBaseInstance

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Draw multiple instances of a set of elements with offset applied to instanced attributes.

C Specification[edit]

void glDrawElementsInstancedBaseInstance( GLenum mode, GLsizei count, GLenum type, const void * indices, GLsizei instancecount, GLuint baseinstance );

Parameters[edit]

mode - Specifies what kind of primitives to render. Symbolic constants GL_POINTSGL_LINE_STRIPGL_LINE_LOOPGL_LINESGL_LINE_STRIP_ADJACENCY, GL_LINES_ADJACENCYGL_TRIANGLE_STRIPGL_TRIANGLE_FANGL_TRIANGLESGL_TRIANGLE_STRIP_ADJACENCYGL_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_BYTEGL_UNSIGNED_SHORT, or GL_UNSIGNED_INT.
indices - Specifies a pointer to the location where the indices are stored.
instancecount - 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[edit]

glDrawElementsInstancedBaseInstance behaves identically to glDrawElements except that instancecount 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 < instancecount ; i++) {
           instanceID = i;
           glDrawElements(mode, count, type, indices);
       }
       instanceID = 0;
   }

Specific vertex attributes may be classified asinstancedthrough 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 [math][\frac{glInstanceID}{divisor}]+baseInstance[/math]. Note that baseinstance does not affect the shader-visible value of gl_InstanceID.

Notes[edit]

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

GL_LINE_STRIP_ADJACENCYGL_LINES_ADJACENCYGL_TRIANGLE_STRIP_ADJACENCY and GL_TRIANGLES_ADJACENCY are available only if the GL version is 3.2 or greater.

Errors[edit]

GL_INVALID_ENUM is generated if mode is not one of GL_POINTSGL_LINE_STRIPGL_LINE_LOOPGL_LINESGL_TRIANGLE_STRIPGL_TRIANGLE_FAN, or GL_TRIANGLES.

GL_INVALID_VALUE is generated if count or instancecount is 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.

Version Support[edit]

 glDrawElementsInstancedBaseInstance  4.2+

See Also[edit]

glDrawElementsglDrawArraysInstanced 

Copyright[edit]

Copyright© 2011-2014 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/.