glDrawArraysInstancedBaseInstance — draw multiple instances of a range of elements with offset applied to instanced attributes
void glDrawArraysInstancedBaseInstance( | GLenum mode, |
| GLint first, | |
| GLsizei count, | |
| GLsizei primcount, | |
GLuint baseinstance); |
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, GL_TRIANGLE_STRIP_ADJACENCY and GL_PATCHES
are accepted.
firstSpecifies the starting index in the enabled arrays.
countSpecifies the number of indices to be rendered.
primcountSpecifies the number of instances of the specified range of indices to be rendered.
baseinstanceSpecifies the base instance for use in fetching instanced vertex attributes.
glDrawArraysInstancedBaseInstance 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.
glDrawArraysInstancedBaseInstance 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;
}
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:
baseinstance does not affect the shader-visible value of gl_InstanceID.
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.
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/.