[vtkusers] Transparency issue beetween actors

[Bertrand de Boisdeffre]

Hi,
I have an issue about actors transparency. I try to display in a 3D scene,
some volumes ( vtkPolyData are the source) intersected by a plane which has
an image texture.
I manage to display correctly all my actors, but when i set an actor opacity
to a value different to 1, if this actor is located beetween the camera and
the "image plane", it diseapears.

Here is my code to built my "image plane":

 vtkActor sliceActor = new vtkActor();
            // ImageSlice full path
            string imageFullPath =
System.IO.Path.GetFullPath(xmlBinding.GetSlice(XmlSlice.SliceRef).pictureRelativePathWithOverlays);


            // Read the file
            vtkPNGReader imageReader = new vtkPNGReader();
            if(System.IO.File.Exists(imageFullPath))
            {
                imageReader.SetFileName(imageFullPath);
                imageReader.Update();

 vtkPlaneSource plane = vtkPlaneSource.New();
                plane.SetOrigin(0, 0, 0);

                if (XmlSlice.SliceRef != 0)
                {
                    plane.SetPoint1(511 * THOutline.PIXELSIZE, 0, 0);
                    plane.SetPoint2(0, 0, -674 * THOutline.PIXELSIZE);
                    plane.SetXResolution(1);
                    plane.SetYResolution(1);

                }
                else
                {
                    plane.SetPoint1(0, 511 * THOutline.PIXELSIZE, 0);
                    plane.SetPoint2(0, 0, -674 * THOutline.PIXELSIZE);
                    plane.SetXResolution(1);
                    plane.SetYResolution(1);
                }
                plane.SetCenter(XmlSlice.SlicePos.Xum,
XmlSlice.SlicePos.Yum, XmlSlice.SlicePos.Zum + (674 * THOutline.PIXELSIZE /
2 - this.GetFocalPositionImageTopUm()));

                vtkPolyDataMapper sliceMapper = vtkPolyDataMapper.New();
                sliceMapper.SetInput(plane.GetOutput());



                sliceActor.SetMapper(sliceMapper);

                vtkTexture sliceTexture = vtkTexture.New();
                sliceTexture.SetInput(imageReader.GetOutput());
                sliceTexture.InterpolateOn();
                sliceTexture.SetQualityTo32Bit();

                sliceActor.SetTexture(sliceTexture);

                }
            return sliceActor;

So the image is correctly display, but if i had an a other actor as in this
schema (top view):

                           _________                                 : image
slice actor

                         00000000000                               : "volume
actor"


                                   -
                                  | |
: camera


if volume actor opacity = 1, all work well.
if volume actor opacity != 1 =>

                            _________       : image slice actor


                           0               00   : "volume actor"


                                   -
                                  | |               : camera


I make some researches on web, and i found (maybe) a solution : using
"vtkDephtSortPolyData but I am not sure to know how it works ( and maybe it
is not the solution) .

So i ask your help.

Best Regards,
-- 
Bertrand de Boisdeffre
Etudiant 2A  SICOM Phelma Grenoble-INP
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