Bullet algorithm having trouble with rotation on the X - c++

Question

Here is what I'm trying to do. I'm trying to make a bullet out of the center of the screen. I have an x and y rotation angle. The problem is the Y (which is modified by rotation on the x) is really not working as intended. Here is what I have.
float yrotrad, xrotrad;
yrotrad = (Camera.roty / 180.0f * 3.141592654f);
xrotrad = (Camera.rotx / 180.0f * 3.141592654f);
Vertex3f Pos;
// get camera position
pls.x = Camera.x;
pls.y = Camera.y;
pls.z = Camera.z;
for(float i = 0; i < 60; i++)
{
//add the rotation vector
pls.x += float(sin(yrotrad)) ;
pls.z -= float(cos(yrotrad)) ;
pls.y += float(sin(twopi - xrotrad));
//translate camera coords to cube coords
Pos.x = ceil(pls.x / 3);
Pos.y = ceil((pls.y) / 3);
Pos.z = ceil(pls.z / 3);
if(!CubeIsEmpty(Pos.x,Pos.y,Pos.z)) //remove first cube that made contact
{
delete GetCube(Pos.x,Pos.y,Pos.z);
SetCube(0,Pos.x,Pos.y,Pos.z);
return;
}
}
This is almost identical to how I move the player, I add the directional vector to the camera then find which cube the player is on. If I remove the pls.y += float(sin(twopi - xrotrad)); then I clearly see that on the X and Z, everything is pointing as it should. When I add pls.y += float(sin(twopi - xrotrad)); then it almost works, but not quite, what I observed from rendering out spheres of the trajector is that the furthur up or down I look, the more offset it becomes rather than stay alligned to the camera's center. What am I doing wrong?
Thanks
What basically happens is very difficult to explain, I'd expect the bullet at time 0 to always be at the center of the screen, but it behaves oddly. If i'm looking straight at the horizon to +- 20 degrees upward its fine but then it starts not following any more.
I set up my matrix like this:
void CCubeGame::SetCameraMatrix()
{
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glRotatef(Camera.rotx,1,0,0);
glRotatef(Camera.roty,0,1,0);
glRotatef(Camera.rotz,0,0,1);
glTranslatef(-Camera.x , -Camera.y,-Camera.z );
}
and change the angle like this:
void CCubeGame::MouseMove(int x, int y)
{
if(!isTrapped)
return;
int diffx = x-lastMouse.x;
int diffy = y-lastMouse.y;
lastMouse.x = x;
lastMouse.y = y;
Camera.rotx += (float) diffy * 0.2;
Camera.roty += (float) diffx * 0.2;
if(Camera.rotx > 90)
{
Camera.rotx = 90;
}
if(Camera.rotx < -90)
{
Camera.rotx = -90;
}
if(isTrapped)
if (fabs(ScreenDimensions.x/2 - x) > 1 || fabs(ScreenDimensions.y/2 - y) > 1) {
resetPointer();
}
}

Answer 1

You need to scale X and Z by cos(xradrot). (In other words, multiply by cos(xradrot)).
Imagine you're pointing straight down the Z axis but looking straight up. You don't want the bullet to shoot down the Z axis at all, this is why you need to scale it. (It's basically the same thing that you're doing between X and Z, but now doing it on the XZ vector and Y.)
pls.x += float(sin(yrotrad)*cos(xrotrad)) ;
pls.z -= float(cos(yrotrad)*cos(xrotrad)) ;
pls.y += float(sin(twopi - xrotrad));