NAME

glDrawArraysInstanced - draw multiple instances of a range of elements

C SPECIFICATION

void glDrawArraysInstanced(GLenum mode, GLint first, GLsizei count, GLsizei primcount);

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_TRIANGLES GL_LINES_ADJACENCY, GL_LINE_STRIP_ADJACENCY, GL_TRIANGLES_ADJACENCY andGL_TRIANGLE_STRIP_ADJACENCY 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.

DESCRIPTION

glDrawArraysInstanced 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.

glDrawArraysInstanced 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;
    }

NOTES

glDrawArraysInstanced 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 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.