I have a simple camera class working in directx 11 allowing moving forward and rotating left and right. I'm trying to implement strafing into it but having some problems.

The strafing works when there's no camera rotation, so when the camera starts at 0, 0, 0. But after rotating the camera in either direction it seems to strafe at an angle or inverted or just some odd stuff.

Here is a video uploaded to Dropbox showing this behavior. https://dl.dropboxusercontent.com/u/2873587/IncorrectStrafing.mp4

And here is my camera class. I have a hunch that it's related to the calculation for camera position. I tried various different calculations in strafe and they all seem to follow the same pattern and same behavior. Also the m_camera_rotation represents the Y rotation, as pitching isn't implemented yet.

#include "camera.h"


camera::camera(float x, float y, float z, float initial_rotation) {
m_x = x;
m_y = y;
m_z = z;
m_camera_rotation = initial_rotation;

updateDXZ();
}


camera::~camera(void)
{
}

void camera::updateDXZ() {
m_dx = sin(m_camera_rotation * (XM_PI/180.0));
m_dz = cos(m_camera_rotation * (XM_PI/180.0));
}

void camera::Rotate(float amount) {
m_camera_rotation += amount;

updateDXZ();
}

void camera::Forward(float step) {
m_x += step * m_dx;
m_z += step * m_dz;
}

void camera::strafe(float amount) {
float yaw = (XM_PI/180.0) * m_camera_rotation;

m_x += cosf( yaw ) * amount;
m_z += sinf( yaw ) * amount;
}

XMMATRIX camera::getViewMatrix() {
updatePosition();

return XMMatrixLookAtLH(m_position, m_lookat, m_up);
}

void camera::updatePosition() {
m_position = XMVectorSet(m_x, m_y, m_z, 0.0);
m_lookat = XMVectorSet(m_x + m_dx, m_y, m_z + m_dz, 0.0);
m_up = XMVectorSet(0.0, 1.0, 0.0, 0.0);
}