NAME

glDrawElementsInstanced - draw multiple instances of a set of elements

C SPECIFICATION

void glDrawElementsInstanced(GLenum mode, GLsizei count, GLenum type, const void * indices, GLsizei primcount);

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 and GL_TRIANGLES_ADJACENCY 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.

DESCRIPTION

glDrawElementsInstanced 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.

glDrawElementsInstanced 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;
    }

NOTES

glDrawElementsInstanced is available only if the GL version is 3.1 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.