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glDrawElementsInstancedBaseInstance

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 instancecount,
  GLuint 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.

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

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 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 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

OpenGL Version
Function / Feature Name 2.0 2.1 3.0 3.1 3.2 3.3 4.0 4.1 4.2 4.3 4.4 4.5
glDrawElementsInstancedBaseInstance - - - - - - - - ✔ ✔ ✔ ✔
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