Why does my OpenGL reflection fail to clip to the stenciled area? - opengl

Question

The below code is nearly identical to the code retrieved from this NeHe tutorial. The only difference between my code and the code on the tutorial is that I am using SFML for window context, which should not be relevant. To view the entire source code, go here. A snippet of the relevant code is below (the comments are from NeHe):
// Clip Plane Equations
double eqr[] = {0.0f,-1.0f, 0.0f, 0.0f}; // Plane Equation glColorMask(0,0,0,0); // Set Color Mask
glEnable(GL_STENCIL_TEST); // Enable Stencil Buffer For "marking" The Floor
glStencilFunc(GL_ALWAYS, 1, 1); // Always Passes, 1 Bit Plane, 1 As Mask
glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE); // We Set The Stencil Buffer To 1 Where We Draw Any Polygon
// Keep If Test Fails, Keep If Test Passes But Buffer Test Fails
// Replace If Test Passes
glDisable(GL_DEPTH_TEST); // Disable Depth Testing
DrawFloor(); // Draw The Floor (Draws To The Stencil Buffer)
// We Only Want To Mark It In The Stencil Buffer
glEnable(GL_DEPTH_TEST); // Enable Depth Testing
glColorMask(1,1,1,1); // Set Color Mask to TRUE, TRUE, TRUE, TRUE
glStencilFunc(GL_EQUAL, 1, 1); // We Draw Only Where The Stencil Is 1
// (I.E. Where The Floor Was Drawn)
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP); // Don't Change The Stencil Buffer
glEnable(GL_CLIP_PLANE0); // Enable Clip Plane For Removing Artifacts
// (When The Object Crosses The Floor)
glClipPlane(GL_CLIP_PLANE0, eqr); // Equation For Reflected Objects
glPushMatrix(); // Push The Matrix Onto The Stack
glScalef(1.0f, -1.0f, 1.0f); // Mirror Y Axis
glLightfv(GL_LIGHT0, GL_POSITION, LightPos); // Set Up Light0
glTranslatef(0.0f, height, 0.0f); // Position The Object
DrawObject(); // Draw The Sphere (Reflection)
glPopMatrix(); // Pop The Matrix Off The Stack
glDisable(GL_CLIP_PLANE0); // Disable Clip Plane For Drawing The Floor
glDisable(GL_STENCIL_TEST); // We Don't Need The Stencil Buffer Any More (Disable)
glLightfv(GL_LIGHT0, GL_POSITION, LightPos); // Set Up Light0 Position
glEnable(GL_BLEND); // Enable Blending (Otherwise The Reflected Object Wont Show)
glDisable(GL_LIGHTING); // Since We Use Blending, We Disable Lighting
glColor4f(1.0f, 1.0f, 1.0f, 0.8f); // Set Color To White With 80% Alpha
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // Blending Based On Source Alpha And 1 Minus Dest Alpha
DrawFloor(); // Draw The Floor To The Screen
glEnable(GL_LIGHTING); // Enable Lighting
glDisable(GL_BLEND); // Disable Blending
glTranslatef(0.0f, height, 0.0f); // Position The Ball At Proper Height
DrawObject();
The final result of this code can be seen below:
How do I alter the above code to cause the bottom (reflected) sphere to appear only on the plane instead of outside of it.

Answer 1

Well, do you actually create a GL context with a stencil buffer? The only relevant line for context creation in your code seems to be
f::RenderWindow window(sf::VideoMode(800, 600, 32), "Test");
and that is not very specific. I don't know SFML, but why do you think changing the code for context creation isn't relevant here?