I am quite new to OpenGL, I have managed after long trial and error to integrate Nehe's Cel-Shading rendering with my Model loaders, and have them drawn using the Toon shade and outline AND their original texture at the same time. The result is actually a very nice Cel Shading effect of the model texture, but it is havling the speed of the program, it's quite very slow even with just 3 models on screen...

Since the result was kind of hacked together, I am thinking that maybe I am performing some extra steps or extra rendering tasks that maybe are not needed, and are slowing down the game? Something unnecessary that maybe you guys could spot?

Both MD2 and 3DS loader have an InitToon() function called upon creation to load the shader

initToon(){

    int i;                                                        // Looping Variable ( NEW )
    char Line[255];                                                // Storage For 255 Characters ( NEW )
    float shaderData[32][3];                                    // Storate For The 96 Shader Values ( NEW )
    FILE *In = fopen ("Shader.txt", "r");                        // Open The Shader File ( NEW )

    if (In)                                                        // Check To See If The File Opened ( NEW )
    {
        for (i = 0; i < 32; i++)                                // Loop Though The 32 Greyscale Values ( NEW )
        {
            if (feof (In))                                        // Check For The End Of The File ( NEW )
                break;

            fgets (Line, 255, In);                                // Get The Current Line ( NEW )

            shaderData[i][0] = shaderData[i][1] = shaderData[i][2] = float(atof (Line)); // Copy Over The Value ( NEW )
        }

        fclose (In);                                            // Close The File ( NEW )
    }

    else
        return false;                                            // It Went Horribly Horribly Wrong ( NEW )

    glGenTextures (1, &shaderTexture[0]);                        // Get A Free Texture ID ( NEW )

    glBindTexture (GL_TEXTURE_1D, shaderTexture[0]);            // Bind This Texture. From Now On It Will Be 1D ( NEW )

    // For Crying Out Loud Don't Let OpenGL Use Bi/Trilinear Filtering! ( NEW )
    glTexParameteri (GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);    
    glTexParameteri (GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glTexImage1D (GL_TEXTURE_1D, 0, GL_RGB, 32, 0, GL_RGB , GL_FLOAT, shaderData);    // Upload ( NEW )


}

This is the drawing for the animated MD2 model:

void MD2Model::drawToon() {
    float        outlineWidth    = 3.0f;                                // Width Of The Lines ( NEW )
    float        outlineColor[3]    = { 0.0f, 0.0f, 0.0f };                // Color Of The Lines ( NEW )


// ORIGINAL PART OF THE FUNCTION


    //Figure out the two frames between which we are interpolating
    int frameIndex1 = (int)(time * (endFrame - startFrame + 1)) + startFrame;
    if (frameIndex1 > endFrame) {
        frameIndex1 = startFrame;
    }

    int frameIndex2;
    if (frameIndex1 < endFrame) {
        frameIndex2 = frameIndex1 + 1;
    }
    else {
        frameIndex2 = startFrame;
    }

    MD2Frame* frame1 = frames + frameIndex1;
    MD2Frame* frame2 = frames + frameIndex2;

    //Figure out the fraction that we are between the two frames
    float frac =
        (time - (float)(frameIndex1 - startFrame) /
         (float)(endFrame - startFrame + 1)) * (endFrame - startFrame + 1);


// I ADDED THESE FROM NEHE'S TUTORIAL FOR FIRST PASS (TOON SHADE)

    glHint (GL_LINE_SMOOTH_HINT, GL_NICEST);                // Use The Good Calculations ( NEW )
    glEnable (GL_LINE_SMOOTH);
    // Cel-Shading Code //
    glEnable (GL_TEXTURE_1D);                                    // Enable 1D Texturing ( NEW )
    glBindTexture (GL_TEXTURE_1D, shaderTexture[0]);            // Bind Our Texture ( NEW )

    glColor3f (1.0f, 1.0f, 1.0f);                                // Set The Color Of The Model ( NEW )

// ORIGINAL DRAWING CODE

    //Draw the model as an interpolation between the two frames
    glBegin(GL_TRIANGLES);
    for(int i = 0; i < numTriangles; i++) {
        MD2Triangle* triangle = triangles + i;
        for(int j = 0; j < 3; j++) {
            MD2Vertex* v1 = frame1->vertices + triangle->vertices[j];
            MD2Vertex* v2 = frame2->vertices + triangle->vertices[j];
            Vec3f pos = v1->pos * (1 - frac) + v2->pos * frac;
            Vec3f normal = v1->normal * (1 - frac) + v2->normal * frac;
            if (normal[0] == 0 && normal[1] == 0 && normal[2] == 0) {
                normal = Vec3f(0, 0, 1);
            }
            glNormal3f(normal[0], normal[1], normal[2]);

            MD2TexCoord* texCoord = texCoords + triangle->texCoords[j];
            glTexCoord2f(texCoord->texCoordX, texCoord->texCoordY);
            glVertex3f(pos[0], pos[1], pos[2]);
        }
    }
    glEnd();

// ADDED THESE FROM NEHE'S FOR SECOND PASS (OUTLINE)

    glDisable (GL_TEXTURE_1D);                                    // Disable 1D Textures ( NEW )


    glEnable (GL_BLEND);                                    // Enable Blending ( NEW )
        glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);        // Set The Blend Mode ( NEW )

        glPolygonMode (GL_BACK, GL_LINE);                        // Draw Backfacing Polygons As Wireframes ( NEW )
        glLineWidth (outlineWidth);                                // Set The Line Width ( NEW )

        glCullFace (GL_FRONT);                                    // Don't Draw Any Front-Facing Polygons ( NEW )

        glDepthFunc (GL_LEQUAL);                                // Change The Depth Mode ( NEW )

        glColor3fv (&outlineColor[0]);                            // Set The Outline Color ( NEW )


// HERE I AM PARSING THE VERTICES AGAIN (NOT IN THE ORIGINAL FUNCTION) FOR THE OUTLINE AS PER NEHE'S TUT

        glBegin (GL_TRIANGLES);                                    // Tell OpenGL What We Want To Draw
        for(int i = 0; i < numTriangles; i++) {
        MD2Triangle* triangle = triangles + i;
        for(int j = 0; j < 3; j++) {
            MD2Vertex* v1 = frame1->vertices + triangle->vertices[j];
            MD2Vertex* v2 = frame2->vertices + triangle->vertices[j];
            Vec3f pos = v1->pos * (1 - frac) + v2->pos * frac;
            Vec3f normal = v1->normal * (1 - frac) + v2->normal * frac;
            if (normal[0] == 0 && normal[1] == 0 && normal[2] == 0) {
                normal = Vec3f(0, 0, 1);
            }
            glNormal3f(normal[0], normal[1], normal[2]);

            MD2TexCoord* texCoord = texCoords + triangle->texCoords[j];
            glTexCoord2f(texCoord->texCoordX, texCoord->texCoordY);
            glVertex3f(pos[0], pos[1], pos[2]);
        }
    }
        glEnd ();                                                // Tell OpenGL We've Finished

        glDepthFunc (GL_LESS);                                    // Reset The Depth-Testing Mode ( NEW )

        glCullFace (GL_BACK);                                    // Reset The Face To Be Culled ( NEW )

        glPolygonMode (GL_BACK, GL_FILL);                        // Reset Back-Facing Polygon Drawing Mode ( NEW )

        glDisable (GL_BLEND);    
}

Whereas this is the drawToon function in the 3DS loader

void Model_3DS::drawToon()
{

    float        outlineWidth    = 3.0f;                                // Width Of The Lines ( NEW )
    float        outlineColor[3]    = { 0.0f, 0.0f, 0.0f };                // Color Of The Lines ( NEW )

//ORIGINAL CODE

    if (visible)
    {
    glPushMatrix();

        // Move the model
        glTranslatef(pos.x, pos.y, pos.z);

        // Rotate the model
        glRotatef(rot.x, 1.0f, 0.0f, 0.0f);
        glRotatef(rot.y, 0.0f, 1.0f, 0.0f);
        glRotatef(rot.z, 0.0f, 0.0f, 1.0f);

        glScalef(scale, scale, scale);

        // Loop through the objects
        for (int i = 0; i < numObjects; i++)
        {
            // Enable texture coordiantes, normals, and vertices arrays
            if (Objects[i].textured)
                glEnableClientState(GL_TEXTURE_COORD_ARRAY);
            if (lit)
                glEnableClientState(GL_NORMAL_ARRAY);
            glEnableClientState(GL_VERTEX_ARRAY);

            // Point them to the objects arrays
            if (Objects[i].textured)
                glTexCoordPointer(2, GL_FLOAT, 0, Objects[i].TexCoords);
            if (lit)
                glNormalPointer(GL_FLOAT, 0, Objects[i].Normals);
            glVertexPointer(3, GL_FLOAT, 0, Objects[i].Vertexes);

            // Loop through the faces as sorted by material and draw them
            for (int j = 0; j < Objects[i].numMatFaces; j ++)
            {
                // Use the material's texture
                Materials[Objects[i].MatFaces[j].MatIndex].tex.Use();


// AFTER THE TEXTURE IS APPLIED I INSERT THE TOON FUNCTIONS HERE (FIRST PASS)



                    glHint (GL_LINE_SMOOTH_HINT, GL_NICEST);                // Use The Good Calculations ( NEW )
                    glEnable (GL_LINE_SMOOTH);
                    // Cel-Shading Code //
                    glEnable (GL_TEXTURE_1D);                                    // Enable 1D Texturing ( NEW )
                    glBindTexture (GL_TEXTURE_1D, shaderTexture[0]);            // Bind Our Texture ( NEW )

                        glColor3f (1.0f, 1.0f, 1.0f);                                // Set The Color Of The Model ( NEW )



                glPushMatrix();

                    // Move the model
                    glTranslatef(Objects[i].pos.x, Objects[i].pos.y, Objects[i].pos.z);

                    // Rotate the model

                    glRotatef(Objects[i].rot.z, 0.0f, 0.0f, 1.0f);
                    glRotatef(Objects[i].rot.y, 0.0f, 1.0f, 0.0f);
                    glRotatef(Objects[i].rot.x, 1.0f, 0.0f, 0.0f);

                    // Draw the faces using an index to the vertex array
                    glDrawElements(GL_TRIANGLES, Objects[i].MatFaces[j].numSubFaces, GL_UNSIGNED_SHORT, Objects[i].MatFaces[j].subFaces);

                glPopMatrix();
            }



                glDisable (GL_TEXTURE_1D);                                    // Disable 1D Textures ( NEW )


// THIS IS AN ADDED SECOND PASS AT THE VERTICES FOR THE OUTLINE


    glEnable (GL_BLEND);                                    // Enable Blending ( NEW )
        glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);        // Set The Blend Mode ( NEW )

        glPolygonMode (GL_BACK, GL_LINE);                        // Draw Backfacing Polygons As Wireframes ( NEW )
        glLineWidth (outlineWidth);                                // Set The Line Width ( NEW )

        glCullFace (GL_FRONT);                                    // Don't Draw Any Front-Facing Polygons ( NEW )

        glDepthFunc (GL_LEQUAL);                                // Change The Depth Mode ( NEW )

        glColor3fv (&outlineColor[0]);                            // Set The Outline Color ( NEW )

        for (int j = 0; j < Objects[i].numMatFaces; j ++)
            {
        glPushMatrix();

                    // Move the model
                    glTranslatef(Objects[i].pos.x, Objects[i].pos.y, Objects[i].pos.z);

                    // Rotate the model
                                    glRotatef(Objects[i].rot.z, 0.0f, 0.0f, 1.0f);
                    glRotatef(Objects[i].rot.y, 0.0f, 1.0f, 0.0f);
                    glRotatef(Objects[i].rot.x, 1.0f, 0.0f, 0.0f);

                    // Draw the faces using an index to the vertex array
                    glDrawElements(GL_TRIANGLES, Objects[i].MatFaces[j].numSubFaces, GL_UNSIGNED_SHORT, Objects[i].MatFaces[j].subFaces);

                glPopMatrix();


        }

                glDepthFunc (GL_LESS);                                    // Reset The Depth-Testing Mode ( NEW )

        glCullFace (GL_BACK);                                    // Reset The Face To Be Culled ( NEW )

        glPolygonMode (GL_BACK, GL_FILL);                        // Reset Back-Facing Polygon Drawing Mode ( NEW )

        glDisable (GL_BLEND);

glPopMatrix();
}

Finally this is the tex.Use() function that loads a BMP texture and somehow gets blended perfectly with the Toon shading

void GLTexture::Use()
{
    glEnable(GL_TEXTURE_2D);                                // Enable texture mapping
    glBindTexture(GL_TEXTURE_2D, texture[0]);                // Bind the texture as the current one

}