Add mirror routine

[yuripourre]

The effects of specular reflection can be approximated by a two-pass technique using the stencil buffer. During the first pass, we render the reflected image of the scene. During the second pass, we render the non-reflected view of the scene, using the stencil buffer to prevent the reflected image from being drawn over. 

https://www.opengl.org/archives/resources/code/samples/advanced/advanced97/notes/node90.html

It would be interesting to have a method mirror on camera

camera.mirror(plane);
Position and direction would be reflected according to the mirror plane.

Cross product between up and plane may be useful.

LibGDX Snippet:

https://github.com/libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/graphics/Camera.java#L151

Point: Intersector#intersectRayPlane
Axis: 
Angle:

Example (JoGL Port)
http://jerome.jouvie.free.fr/opengl-tutorials/Tutorial23.php

[yuripourre]

Another java example
https://www.java-tips.org/other-api-tips-100035/112-jogl/1701-clipping-and-reflections-using-the-stencil-buffer-nehe-tutorial-jogl-port.html

http://forum.lwjgl.org/index.php?topic=1340.0

[yuripourre]

/*
		 * We should clear the stencil buffer like we do with color and depth buffers
		 */
		gl.glClear(IGL.GL_COLOR_BUFFER_BIT | IGL.GL_DEPTH_BUFFER_BIT | IGL.GL_STENCIL_BUFFER_BIT);	//Clear the buffers

		camera.update(getTimer().getTimePassedMillis());
		camera.lookAt(modelView);
		gl.glLoadMatrix(modelView);

		if(renderModeFilled) {
			gl.glPolygonMode(IGL.GL_FRONT_AND_BACK, IGL.GL_FILL);
		}
		else {
			gl.glPolygonMode(IGL.GL_FRONT_AND_BACK, IGL.GL_LINE);
		}

		if(camera.getMovable().equals(light)) {
			Vector3f pos = camera.getPosition(new Vector3f());
			lightPos[0] = pos.getX();
			lightPos[1] = pos.getY();
			lightPos[2] = pos.getZ();
		}

		/* Fill with one stencil buffer where the ground is */

		gl.glColorMask(false, false, false, false);				//Disable drawing of r, g, b & a
		gl.glDepthMask(false);
		gl.glEnable(IGL.GL_STENCIL_TEST);						//Enable Stencil test
		gl.glStencilFunc(IGL.GL_ALWAYS, 1, 1);					//Test always success, value stored in stencil buffer is 1 (second parameter)
		gl.glStencilOp(IGL.GL_KEEP, IGL.GL_KEEP, IGL.GL_REPLACE);	//Replace by 1 when test pass

		drawRectangle_YPlane_VtxUvNrm(gl, -10.0f, -10.0f, 20.0f, 20.0f, 1);

		gl.glDepthMask(true);
		gl.glColorMask(true, true, true, true);					//Enable drawing of r, g, b & a

		/* Reflection */

		gl.glStencilFunc(IGL.GL_EQUAL, 1, 1);					//Draw only where stencil buffer is 1
		gl.glStencilOp(IGL.GL_KEEP, IGL.GL_KEEP, IGL.GL_KEEP);		//Stencil buffer read only

		gl.glPushMatrix();
		gl.glScale(1.0f, -1.0f, 1.0f);						//Mirror Y
		gl.glLight(IGL.GL_LIGHT0, IGL.GL_POSITION, BufferPool.wrap(lightPos));
		gl.glEnable(IGL.GL_LIGHTING);
		drawSpring(gl);
		gl.glDisable(IGL.GL_LIGHTING);
		gl.glPopMatrix();

		gl.glDisable(IGL.GL_STENCIL_TEST);

		/* Draw the ground */

		gl.glEnable(IGL.GL_TEXTURE_2D);
		gl.glBindTexture(IGL.GL_TEXTURE_2D,  texture.id);
		gl.glEnable(IGL.GL_BLEND);
		gl.glBlendFunc(IGL.GL_ONE, IGL.GL_ONE_MINUS_SRC_ALPHA);
		gl.glColor(1.0f, 1.0f, 1.0f, 0.8f);
		drawRectangle_YPlane_VtxUvNrm(gl, -10.0f, -10.0f, 20.0f, 20.0f, 10);
		gl.glColor(1.0f, 1.0f, 1.0f, 1.0f);
		gl.glDisable(IGL.GL_BLEND);
		gl.glDisable(IGL.GL_TEXTURE_2D);

		/* Draw the spring */

		gl.glLight(IGL.GL_LIGHT0, IGL.GL_POSITION, BufferPool.wrap(lightPos));
		gl.glEnable(IGL.GL_LIGHTING);
		drawSpring(gl);
		gl.glDisable(IGL.GL_LIGHTING);

		/* Draw the bulb */
		gl.glTranslate(lightPos[0], lightPos[1], lightPos[2]);
		Shapes.drawSphere(gl, 0.07f, 10, 10, true, null);
		gl.glTranslate(-lightPos[0], -lightPos[1], -lightPos[2]);