My shadow volumes don't move with my light - opengl

Question

I'm currently trying to implement shadow volumes in my opengl world. Right now I'm just focusing on getting the volumes calculated correctly.
Right now I have a teapot that's rendered, and I can get it to generate some shadow volumes, however they always point directly to the left of the teapot. No matter where I move my light(and I can tell that I'm actually moving the light because the teapot is lit with diffuse lighting), the shadow volumes always go straight left.
The method I'm using to create the volumes is:
1. Find silhouette edges by looking at every triangle in the object. If the triangle isn't lit up(tested with the dot product), then skip it. If it is lit, then check all of its edges. If the edge is currently in the list of silhouette edges, remove it. Otherwise add it.
2. Once I have all the silhouette edges, I go through each edge creating a quad with one vertex at each vertex of the edge, and the other two just extended away from the light.
Here is my code that does it all:
void getSilhoueteEdges(Model model, vector<Edge> &edges, Vector3f lightPos) {
//for every triangle
// if triangle is not facing the light then skip
// for every edge
// if edge is already in the list
// remove
// else
// add
vector<Face> faces = model.faces;
//for every triangle
for ( unsigned int i = 0; i < faces.size(); i++ ) {
Face currentFace = faces.at(i);
//if triangle is not facing the light
//for this i'll just use the normal of any vertex, it should be the same for all of them
Vector3f v1 = model.vertices[currentFace.vertices[0] - 1];
Vector3f n1 = model.normals[currentFace.normals[0] - 1];
Vector3f dirToLight = lightPos - v1;
dirToLight.normalize();
float dot = n1.dot(dirToLight);
if ( dot <= 0.0f )
continue; //then skip
//lets get the edges
//v1,v2; v2,v3; v3,v1
Vector3f v2 = model.vertices[currentFace.vertices[1] - 1];
Vector3f v3 = model.vertices[currentFace.vertices[2] - 1];
Edge e[3];
e[0] = Edge(v1, v2);
e[1] = Edge(v2, v3);
e[2] = Edge(v3, v1);
//for every edge
//triangles only have 3 edges so loop 3 times
for ( int j = 0; j < 3; j++ ) {
if ( edges.size() == 0 ) {
edges.push_back(e[j]);
continue;
}
bool wasRemoved = false;
//if edge is in the list
for ( unsigned int k = 0; k < edges.size(); k++ ) {
Edge tempEdge = edges.at(k);
if ( tempEdge == e[j] ) {
edges.erase(edges.begin() + k);
wasRemoved = true;
break;
}
}
if ( ! wasRemoved )
edges.push_back(e[j]);
}
}
}
void extendEdges(vector<Edge> edges, Vector3f lightPos, GLBatch &batch) {
float extrudeSize = 100.0f;
batch.Begin(GL_QUADS, edges.size() * 4);
for ( unsigned int i = 0; i < edges.size(); i++ ) {
Edge edge = edges.at(i);
batch.Vertex3f(edge.v1.x, edge.v1.y, edge.v1.z);
batch.Vertex3f(edge.v2.x, edge.v2.y, edge.v2.z);
Vector3f temp = edge.v2 + (( edge.v2 - lightPos ) * extrudeSize);
batch.Vertex3f(temp.x, temp.y, temp.z);
temp = edge.v1 + ((edge.v1 - lightPos) * extrudeSize);
batch.Vertex3f(temp.x, temp.y, temp.z);
}
batch.End();
}
void createShadowVolumesLM(Vector3f lightPos, Model model) {
getSilhoueteEdges(model, silhoueteEdges, lightPos);
extendEdges(silhoueteEdges, lightPos, boxShadow);
}
I have my light defined as and the main shadow volume generation method is called by:
Vector3f vLightPos = Vector3f(-5.0f,0.0f,2.0f);
createShadowVolumesLM(vLightPos, boxModel);
All of my code seems self documented in places I don't have any comments, but if there are any confusing parts, let me know.
I have a feeling it's just a simple mistake I over looked. Here is what it looks like with and without the shadow volumes being rendered.

Answer 1

It would seem you aren't transforming the shadow volumes. You either need to set the model view matrix on them so they get transformed the same as the rest of the geometry. Or you need to transform all the vertices (by hand) into view space and then do the silhouetting and transformation in view space.
Obviously the first method will use less CPU time and would be, IMO, preferrable.