Fragment Operations - Praise for OpenGL ES 30 Programming Guide - page 301

If you have multiple draw buffers in a framebuffer object (see the Multiple
Render Targets section), you can clear a specific draw buffer with the
following calls:

void glClearBufferiv (GLenum buffer , GLint drawBuffer ,
const GLint * value )
void glClearBufferuiv (GLenum buffer , GLint drawBuffer ,
const GLuint * value )
void glClearBufferfv (GLenum buffer , GLint drawBuffer ,
const GLfloat * value )

specifies the type of buffer to clear. Can be
GL_COLOR , GL_FRONT , GL_BACK , GL_FRONT_AND_BACK ,
GL_LEFT , GL_RIGHT , GL_DEPTH ( glClearBufferfv only) or
GL_STENCIL ( glClearBufferiv only).
specifies the draw buffer name to clear. Must be zero
for depth or stencil buffers. Otherwise, must be less than
GL_MAX_DRAW_BUFFERS for color buffers.
specifies a pointer to a four-element vector (for color
buffers) or to a single value (for depth or stencil buffers)
to clear the buffer to.

buffer

drawBuffer

value

To reduce the number of function calls, you can clear the depth and
stencil buffers at the same time using glClearBufferfi .

void glClearBufferfi (GLenum buffer , GLint drawBuffer ,
GLfloat depth , GLint stencil )

specifies the type of buffer to clear; must be
GL_DEPTH_STENCIL
specifies the draw buffer name to clear; must be zero
specifies the value to clear the depth buffer to
specifies the value to clear the stencil buffer to

buffer

drawBuffer
depth
stencil

Using Masks to Control Writing to Framebuffers

You can also control which buffers, or components, in the case of the
color buffer, are writable by specifying a buffer write mask. Before a pixel's