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=pod

=head1 NAME

Prima::OpenGL - Prima extension for OpenGL drawing

=head1 DESCRIPTION

The module allows for programming GL library together with Prima widgets.
L<OpenGL> module does a similar jobs using freeglut GUI library.

=head1 API

=head2 Selection of a GL visual

Before a GL area is used, a GL visual need to be selected first. Currently this
process is done by system-specific search function, so results differ between
win32 and x11.  Namely, x11 is less forgiving, and may fail with error. Also,
win32 and x11 GL defaults are different.

All attributes are passed to function C<context_create> as a hashref (see
description below).  If an option is not set, or set to undef, system default
is used.

=over

=item render ( "direct" or "xserver" )

Excerpt from C<glXCreateContext>:

Specifies whether rendering is to be done with a direct connection to the
graphics system if possible ("direct") or through the X server ("xserver").  If
direct is True, then a direct rendering context is created if the
implementation supports direct rendering, if the connection is to an X server
that is local, and if a direct rendering context is available. (An
implementation may return an indirect context when direct is True.) If direct
is False, then a rendering context that renders through the X server is always
created.  Direct rendering provides a performance advantage in some
implementations.  However, direct rendering contexts cannot be shared outside a
single process, and they may be unable to render to GLX

I here may add that I needed that option when was testing cygwin
implementation of the module in no-X11 environment. I couldn't get my X11
working on windows, and installed one under VirtualBox.  However, the only way
I could connect to X server there was to tell VirtualBox to forward the port
6000 inside the emulator to the host machine's 6000. GLX was happy finding that
the connection was local, and tried to use shared memory or whatever underlies
"direct" connection, and failed, instead of doing a soft fall-back to x11
protocol. The only way to make it work in such condition was explicitly setting
config to "xserver".

Actual for x11 only.

=item pixels ( "rgba" or "paletted" )

Selects either paletted or true-color visual representation.

=item layer INTEGER

x11: Layer zero corresponds to the main frame buffer of the display.  Layer
one is the first overlay frame buffer, level two the second overlay frame
buffer, and so on. Negative buffer levels correspond to underlay frame
buffers.

win32: Provides only three layers, -1, 0, and 1 .

=item double_buffer BOOLEAN

If set, select double buffering.

=item stereo BOOLEAN

If set, select a stereo visual.

=item color_bits INTEGER

Indicates the desired color index buffer size. Usual values are 8, 15, 16, 24, or 32.

=item aux_buffers INTEGER

Indicated the desired number of auxilliary buffers.

=item depth_bits INTEGER 

If this value is zero, visuals with no depth buffer are preferred.  Otherwise,
the largest available depth buffer of at least the minimum size is preferred.

=item stencil_bits INTEGER

Indicates the desired number of stencil bitplanes.  The smallest stencil buffer
of at least the specified size is preferred.  If the desired value is zero,
visuals with no stencil buffer are preferred.

=item red_bits green_bits blue_bits alpha_bits INTEGER

If this value is zero, the smallest available red/green/blue/alpha buffer is
preferred.  Otherwise, the largest available buffer of at least the minimum
size is preferred.
                    
=item accum_red_bits accum_green_bits accum_blue_bits accum_alpha_bits INTEGER

If this value is zero, visuals with no red/green/blue/alpha accumulation buffer
are preferred.  Otherwise, the largest possible accumulation buffer of at least
the minimum size is preferred.

=back

=head2 Methods

=over

=item context_push

Pushes the current GL context on an internal stack; there can be only 32 entries. Returns success flag.

=item context_pop

Pops the top GL context from the stack, and selects it. Returns success flag.

=item is_direct($ctx)