Hi Jeremy,
In the past I've done similar low-level 2-pass rendering in a Drawable,
by doing as Robert suggests. Apply one stateset, draw, apply another,
draw again (same or different geometry).
A Program is just state, so you need to draw something in between
setting different Programs. Otherwise setting the first Program has no
(visible) effect. I know it sounds obvious but I thought I'd just throw
that out there so there's no ambiguity :-)
Hope this helps,
J-S
On 04/09/2012 1:23 PM, Jeremy Moles wrote:
On Tue, 2012-09-04 at 11:05 -0600, Paul Martz wrote:
Doesn't a Drawable's state get applied prior to the call to
Drawable::drawImplementation()? If so, you could just put the _program in your
Drawable's StateSet?
I'm working on a nodekit for NV_path_rendering, which takes an "as of
yet unseen" approach to rendering; new go OpenGL, at any rate. :)
They call it the "Stencil then Cover" approach, and like most 2D vector
drawing libraries, there is a notion of both STROKING _and_ FILLING. In
order to support arbitrary shading on both the affected stroke fragments
and affected fill fragments, I need to be able to potentially set two
different shaders during a single drawable drawImplementation.
Now, having said that--which I potentially should have mentioned in the
first email--does that change any advice you might have? :)
(Thanks for the response, btw... good info.)
It's easy to verify that things are happening in the right order using a
debugger with breakpoints set at your drawImplementation() and also at
Program::apply().
If it doesn't happen as I describe above, then I believe what you're doing below
is the most robust, as that code would work with all other rendering in the
scene graph, both shader and non-shader rendering.
Honestly it's been too long since I played at this level. But I seem to recall
that the difference between:
_program->apply( state );
and
state->apply( _program.get() );
is that the latter tracks the currently bound program, doesn't bother to apply
it if it's already in use, and would probably allow you to remove the call to
setLastAppliedProgramObject(0).
-Paul
On 9/4/2012 9:58 AM, Jeremy Moles wrote:
I am creating a custom Drawable that needs to push a Fragment Shader
into the current rendering state and then, after a single extension
call, subsequently remove this shader from the state.
I have some code I noodled through to make this work, but I feel like
there is probably a better way. It goes something like this:
----------------------------------------
drawImplementaion(RenderInfo& ri) {
State* state = ri.getState();
unsigned int contextID = state->getContextID();
_program.apply(state);
myExtensions->doMycall();
GL2Extensions::Get(contextID, true)->glUseProgram(0);
state->setLastAppliedProgramObject(0);
}
----------------------------------------
Like I said above, this "works", but I feel like there is probably a
cleaner way to achieve what I want. Note that _program is a ref_ptr to a
properly create osg::Program object, since I certainly do NOT want to
recreate all the goodness it provides. :)
Any API advice?
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