Clipping in Orthographics projection

Engines, Libraries and Tools Xith3D Forums
#1

Hi i am trying to clip in Orthographic projection.
In Jogl its done something like this gl.glOrtho(0.0f,3.0f, 0.0f,3.0f, -10f,5f);

In xith i thought in method calculatePerspective(Canvas3D canvas) of View class when its setting projection Matrix with
orthoMesa it sets the ClippingVolume.

Also while calling this particular method in View.java


// TODO Check for the correct frontClipDistance calculation for this projection. This is known that current use of -backClipDistance is ugly and wrong, and better way for //this calculation needed
        projection.orthoMesa(-screenScale, screenScale, -screenScale*canvasHalfHeight, screenScale*canvasHalfHeight,-backClipDistance, backClipDistance);

Here if i don’t supply balance parameters like for left, right say i supply 0,10 than perspective gets totally disoriented. Why this restriction of specifying
all the three pairs in equal and opposite values.

I checked out that the method orthoMesa of Transform3D its same as of Java3D ,so is that means we are not properly multiplying ModelViewMatrix and Projection matrix .

Also is their any other way to take a 2D image of a scene formed by intersection of A Scene And a Plane Specified .

Note : I am trying to write a small CAD Application with help of Xith . So you can Guess why i am working in Orthographic projection.

#2

Clipping is done in two situations in OpenGL (correct me, if I’m saying bullshit):

  • If a Polygon is totally or partly out of the frustum
  • if a scrissor box is defined by glScissor()

The second one is abstracted by the ScissorBox class in Xith3D. User the setScissorBox() method of Groups and all Shapes inside this group will be clipped by this box.

Marvin

#3

You are absolutely right .
In my problem i want to create a frustum in such a way that i can take a 2D view which is generated by intersection of Scene with specified Plane.

Thanks for pointing out ScissorBox class, will go trough it.It will give me a direction to think about 8)