Graphics Reference
In-Depth Information
a continuously smooth animation. Recall that double buffering was
discussed in Chapter 3, “An Introduction to EGL.”
Although every EGL configuration will have a color buffer, the depth and
stencil buffers are optional. However, every EGL implementation must
provide at least one configuration that contains all three of the buffers,
with the depth buffer being at least 16 bits deep, and at least 8 bits for
the stencil buffer.
To include a depth or stencil buffer along with your color buffer, you
need to request them when you specify the attributes for your EGL
configuration. As discussed in Chapter 3, you pass a set of attribute-
value pairs into the EGL that specify the type of rendering surface your
application needs. To include a depth buffer in addition to the color
buffer, you would specify
EGL_DEPTH_SIZE
in the list of attributes
along with the desired bit depth you need. Likewise, you would add
EGL_STENCIL_SIZE
along with the number of required bits to obtain
a stencil buffer.
Our convenience library,
esUtil
, simplifies those operations by merely
allowing you to say that you would like those buffers along with a color
buffer, and it takes care of the rest of the work (requesting a maximally
sized buffer). When using our library, you would add (by means of a bit-
wise or operation)
ES_WINDOW_DEPTH
and
ES_WINDOW_STENCIL
in your
call to
esCreateWindow
. For example,
esCreateWindow ( &esContext, “Application Name”,
window_width, window_height,
ES_WINDOW_RGB | ES_WINDOW_DEPTH |
ES_WINDOW_STENCIL );
OpenGL ES is an interactive rendering system, and it assumes that at
the start of each frame, you'll want to initialize all of the buffers to their
default value. Buffers are cleared by calling the
glClear
function, which
takes a bitmask representing the various buffers that should be cleared to
their specified clear values.
