jit.gl.render + 2D Background

Hi dekam,
Yes, you have to put in some kind of hook because shaders completely
replace the standard OpenGL pipeline. There are a variety of ways to
do this. There is a built in vertex shader variable for accessing
what glColor() sets OpenGL state to. It is attribute vec4 gl_Color.
Another typical way to do this is to have a shader parameter for
output alpha. In the end it depends on if you want an explicit
opacity control or if you want to depend on actual OpenGL state. In
alot of the Jitter shaders, there is an explicit opacity control that
either sets just the final alpha or multiplies the final color by some
constant, including the alpha. This is probably the most
straightforward way to go for pixel processing. If you're doing
shaders on 3D forms other than a videoplane, you may want some more
involved dependency on OpenGL state. Here's some relevant info from
the GLSL spec:

V a r y i n g V a r i a b l e s
Unlike user-defined varying variables, the built-in varying variables
don't have a strict one-to-one
correspondence between the vertex language and the fragment language.
Two sets are provided, one for each language. Their relationship is
described below. The following built-in varying variables are
available to write to in a vertex shader. A particular one should be
written to if any functionality in a corresponding fragment shader or
fixed pipeline uses it or state derived from it. Otherwise, behavior
is undefined.

varying vec4 gl_FrontColor;
varying vec4 gl_BackColor;
varying vec4 gl_FrontSecondaryColor;
varying vec4 gl_BackSecondaryColor;
varying vec4 gl_TexCoord[]; // at most will be gl_MaxTextureCoords
varying float gl_FogFragCoord;

For gl_FogFragCoord, the value written will be used as the "c" value
on page 160 of the OpenGL 1.4 Specification by the fixed functionality
pipeline. For example, if the z-coordinate of the fragment in eye
space is desired as "c", then that' s what the vertex shader should
write into gl_FogFragCoord. As with all arrays, indices used to
subscript gl_TexCoord must either be an integral constant expressions,
or this array must be re-declared by the shader with a size. The size
can be at most gl_MaxTextureCoords. Using indexes close to 0 may aid
the implementation in preserving varying resources. The following
varying variables are available to read from in a fragment shader. The
gl_Color and gl_SecondaryColor names are the same names as attributes
passed to the vertex shader. However, there is no name conflict,
because attributes are visible only in vertex shaders and the
following are only visible in a fragment shader.

varying vec4 gl_Color;
varying vec4 gl_SecondaryColor;
varying vec4 gl_TexCoord[]; // at most will be gl_MaxTextureCoords
varying float gl_FogFragCoord;

The values in gl_Color and gl_SecondaryColor will be derived
automatically by the system from
gl_FrontColor, gl_BackColor, gl_FrontSecondaryColor, and
gl_BackSecondaryColor based on which face is visible.