Creating shadow

OpenGL OpenGL: Basic Coding
1

Hi guys!

I’d like to throw a shadow of a teacup.
I’ve implemented three methods: drawPlanes(), setShadowMat() and display().

drawPlanes() draws two planes: One parallel to the xy-plane and one parallel to the xz-plane respectively.

First plane (xy) is:

Gl.glVertex3f(-20.0f, -20.0f, -3.0f);
Gl.glVertex3f(20.0f, -20.0f, -3.0f);
Gl.glVertex3f(20.0f, 20.0f, -3.0f);
Gl.glVertex3f(-20.0f, 20.0f, -3.0f);

Consequently, the normalvector for the xy-plane is [0,0,1] and xz [0,1,0].

Now I’d like to create the plane equation: APx + BPy + CPz + D = 0
A=Nx, B=Ny, C=Nz, D=-(APx+BPy+CPz), so for the first plane A = 0, B = 0 , C = 1 and D = 3, right?

Cheers, enne

2

Ok, I think it is not so clear what my problem is.
Anyway, I’m sure that my plane equation is ok.

I’ve got one problem: The teapot and the xz-plane are rendered perfectly, only my shadow makes some problems.

Instead of throwing a shadow of the teapot on the xz-plane, the whole plane is colored black.
I think it is a problem with the lighting, but I can’t see any mistakes.

Here’s the method where my plane and my teapot are displayed:

private static void Display()
{
float[] red={1.0f, 0.0f, 0.0f, 1.0f};
float[] planeEq=new float[4];

	Gl.glClear(Gl.GL_COLOR_BUFFER_BIT |   Gl.GL_DEPTH_BUFFER_BIT);
	DrawPlanes();
	Gl.glPushMatrix();
	Gl.glMaterialfv(Gl.GL_FRONT, Gl.GL_DIFFUSE, red);
	Glut.glutSolidTeapot(2);
	Gl.glPopMatrix();

	//display shadow here
	//use displacement for shadow projection plane 
	//to avoid z-buffer artifacts
	//...

    ///test

       planeEq[0] = 0;
       planeEq[1] = 1;
       planeEq[2] = 0;
       planeEq[3] = 3;

   Gl.glPushMatrix();

   //Disable lighting and set shadow-color (black)

     Gl.glDisable(Gl.GL_LIGHTING);
     Gl.glColor3f(0f, 0f, 0f);

    ///set shadow-matrix
     SetShadowMat(planeEq);
   
    //re-draw objects
     DrawPlanes();
     Glut.glutSolidTeapot(2);
     
    //enable lighting
     Gl.glEnable(Gl.GL_LIGHTING);

     Gl.glPopMatrix();

      Glut.glutSwapBuffers();
}

Can anyone please tell me what I’m doing wrong?

Best regards,

enne