Hello Johannes,
Johannes Brunen wrote:
> Hi,
>
> I have a problem of translating some native OpenGL code into OpenSG
> jargon.
>
> Can anyone give me some hints how I should represent the following
> OpenGL code into OpenSG primitves? Additionally, am I going to have
> problems, if I later on try to do some shadowing of my scene, because of
> using the stencil buffer?
I think the ShadowViewport uses FBOs to store the shadow maps and does
the shadow test in a shader.
> Can I save the current stencil buffer for the
> duration of my special task and restore it later after I have finished
> with it?
I don't think so, at the very least not easily.
> To shed some light on the code below. It adds some caps to the clipped
> geometry in order to visualize solid geometry.
>
> drawClipPlaneGeom(int idx)
> {
> // draw quad with clip plane number 'idx' its orientation ...
> }
>
> drawGeometry()
> {
> // some solid geometry
> }
>
> unsigned int cpId[] = {GL_CLIP_PLANE0, GL_CLIP_PLANE1, ...,
> GL_CLIP_PLANE5};
>
> void redraw()
> {
> glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
>
> glEnable(GL_STENCIL_TEST);
>
> for (int i = 0; i < 6; ++i) {
> glClear(GL_STENCIL_BUFFER_BIT);
>
> glStencilFunc(GL_NEVER, 1, 1);
> glStencilOp(GL_INVERT, GL_INVERT, GL_INVERT);
>
> glEnable( cpId[i] );
> drawGeometry();
> glDisable( cpId[i] );
>
> glStencilFunc(GL_EQUAL, 1, 1);
> glStencilOp(GL_KEEP, GL_ZERO, GL_ZERO);
>
> for (int j = 0; j < 6; ++j)
> if (i != j) glEnable( cpId[j] );
> drawClipPlaneGeom( i );
> for (int j = 0; j < 6; ++j)
> if (i != j) glDisable( cpId[j] );
> }
>
> glDisable(GL_STENCIL_TEST);
>
> for (int i = 0; i < 6; ++i)
> glEnable( cpId[i] );
> drawGeometry();
> for (int i = 0; i < 6; ++i)
> glDisable( cpId[i] );
>
> glutSwapBuffers();
> }
>
> Sorry, for bothering with these beginner questions, but I need some
> activation impetus.
hm, this is not exactly a beginner question, playing renderer tricks
like this in general does not work to well with a scenegraph system, but
I (well, it's Dirk's idea to be honest) think this particular case
should be possible:
you need to build a scene like this:
+----------------------------+-----------------------+
| | |
MaterialGroup (mat1) MaterialGroup (mat2) MaterialGroup(mat3)
| | |
Geometry (geo1) Geometry (geo2) Geometry (geo1)
geo1 is the object you want to draw, geo2 is a plane that coincides with
your clip plane.
mat1 has a StencilChunk that clears the stencil buffer first then does
the inversion and a ClipPlaneChunk that enables one clip plane.
mat2 has a StencilChunk that has the settings you use for drawing the
clip planes in you GL code and a ClipPlaneChunk that enables all clip
planes you want to use.
mat 3 is the material you want your actual object to appear in.
Since these operations have to happen in the described order, you need
to set the sort key on the materials to force that order.
To support more than one clip plane you'd have to add more copies of the
left two branches.
I hope this description is not too terse, if you have questions please
feel free to ask for more details.
Hope it helps,
Carsten
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