Cubic Bezier Implementation - c++

Question

I am trying to create a cubic bezier patch and am having a little bit of trouble figuring out where I am messing up the calculations. I have my 16 control points in a 2d array and I am looking to make the grid have 400 points each separated in increments of .05.
The control points are in increments of 20 (so P0,0 is at (0,0,0) and P3,3 is at (60, 0, 60). The grid will be on the xz plane with the y coordinates all 0.
Right now I have the following which gives the same values for x and z on every point:
float Bezier3(int j, float k)
{
switch(j) {
case 0:
return (1 - k) * (1 - k) * (1 - k);
break;
case 1:
return 3*k*((1 - k) * (1 - k));
break;
case 2:
return 3 * (k * k) * (1 - k);
break;
case 3:
return k * k * k;
break;
}
}
void CalcBezier()
{
float u;
float v;
for (int i = 0; i < 20; i++) {
u = 0;
v = 0;
for (int j = 0; j < 20; j++) {
for (int x = 0; x < 4; x++) {
for (int y = 0; y < 4; y++) {
grid[i][j].x += control[x][y].x * Bezier3(x, u) * Bezier3(y, v);
grid[i][j].y += control[x][y].y * Bezier3(x, u) * Bezier3(y, v);
grid[i][j].z += control[x][y].z * Bezier3(x, u) * Bezier3(y, v);
}
}
u+=.05;
v+=.05;
}
}
}
I am not exactly sure where I am going wrong. I am trying to walk columnwise through the grid and calculate each bezier point.
I am also attempting to draw the resulting mesh as a triangle mesh:
void bezier_plane()
{
CalcBezier();
for (int i = 0; i < 19; i++) {
for (int j = 0; j < 19; j++) {
glBegin(GL_TRIANGLE_STRIP);
glVertex3f(grid[i][j].x, grid[i][j].y, grid[i][j].z);
glVertex3f(grid[i][j+1].x, grid[i][j+1].y, grid[i][j+1].z);
glVertex3f(grid[i+1][j].x, grid[i+1][j].y, grid[i+1][j].z);
glVertex3f(grid[i+1][j+1].x, grid[i+1][j+1].y, grid[i+1][j+1].z);
glEnd();
}
}
}

Answer 1

It looks like you are incrementing both u and v inside the inner loop.
Try changing
u+=.05;
v+=.05;
}
to
v+=.05;
}
u+=.05;
And move the reset to zero outside of the loop.
for (int i = 0; i < 20; i++) {
u = 0;
v = 0;
to
u = 0;
for (int i = 0; i < 20; i++) {
v = 0;