void HMDState::GetTimewarpMatrices(ovrEyeType eyeId, ovrPosef renderPose,
ovrMatrix4f twmOut[2])
{
// Get timewarp start/end timing
double timewarpStartEnd[2];
getTimewarpStartEnd(eyeId, timewarpStartEnd);
ovrTrackingState startState = PredictedTrackingState(timewarpStartEnd[0]);
ovrTrackingState endState = PredictedTrackingState(timewarpStartEnd[1]);
Quatf quatFromEye = Quatf(renderPose.Orientation);
quatFromEye.Invert(); // because we need the view matrix, not the camera matrix
Matrix4f timewarpStart, timewarpEnd;
CalculateOrientationTimewarpMatrix(
quatFromEye, startState.HeadPose.ThePose.Orientation, timewarpStart);
CalculateOrientationTimewarpMatrix(
quatFromEye, endState.HeadPose.ThePose.Orientation, timewarpEnd);
twmOut[0] = timewarpStart;
twmOut[1] = timewarpEnd;
}
void FrameTimeManager::GetTimewarpMatrices(ovrHmd hmd, ovrEyeType eyeId,
ovrPosef renderPose, ovrMatrix4f twmOut[2])
{
if (!hmd)
{
return;
}
double timewarpStartEnd[2] = { 0.0, 0.0 };
GetTimewarpPredictions(eyeId, timewarpStartEnd);
ovrSensorState startState = ovrHmd_GetSensorState(hmd, timewarpStartEnd[0]);
ovrSensorState endState = ovrHmd_GetSensorState(hmd, timewarpStartEnd[1]);
if (TimewarpIMUTimeSeconds == 0.0)
TimewarpIMUTimeSeconds = startState.Recorded.TimeInSeconds;
Quatf quatFromStart = startState.Predicted.Pose.Orientation;
Quatf quatFromEnd = endState.Predicted.Pose.Orientation;
Quatf quatFromEye = renderPose.Orientation; //EyeRenderPoses[eyeId].Orientation;
quatFromEye.Invert();
Quatf timewarpStartQuat = quatFromEye * quatFromStart;
Quatf timewarpEndQuat = quatFromEye * quatFromEnd;
Matrix4f timewarpStart(timewarpStartQuat);
Matrix4f timewarpEnd(timewarpEndQuat);
// The real-world orientations have: X=right, Y=up, Z=backwards.
// The vectors inside the mesh are in NDC to keep the shader simple: X=right, Y=down, Z=forwards.
// So we need to perform a similarity transform on this delta matrix.
// The verbose code would look like this:
/*
Matrix4f matBasisChange;
matBasisChange.SetIdentity();
matBasisChange.M[0][0] = 1.0f;
matBasisChange.M[1][1] = -1.0f;
matBasisChange.M[2][2] = -1.0f;
Matrix4f matBasisChangeInv = matBasisChange.Inverted();
matRenderFromNow = matBasisChangeInv * matRenderFromNow * matBasisChange;
*/
// ...but of course all the above is a constant transform and much more easily done.
// We flip the signs of the Y&Z row, then flip the signs of the Y&Z column,
// and of course most of the flips cancel:
// +++ +-- +--
// +++ -> flip Y&Z columns -> +-- -> flip Y&Z rows -> -++
// +++ +-- -++
timewarpStart.M[0][1] = -timewarpStart.M[0][1];
timewarpStart.M[0][2] = -timewarpStart.M[0][2];
timewarpStart.M[1][0] = -timewarpStart.M[1][0];
timewarpStart.M[2][0] = -timewarpStart.M[2][0];
timewarpEnd .M[0][1] = -timewarpEnd .M[0][1];
timewarpEnd .M[0][2] = -timewarpEnd .M[0][2];
timewarpEnd .M[1][0] = -timewarpEnd .M[1][0];
timewarpEnd .M[2][0] = -timewarpEnd .M[2][0];
twmOut[0] = timewarpStart;
twmOut[1] = timewarpEnd;
}
