# DX11 Camera Rotation in DX11

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Hi People :>

So I recently got started with DX11 and graphics programming in general. I followed tutorials and a book on how to understand and set up the basic stuff. At this point I've managed putting a colored cube in a grey window. I also implemented my own input system (mouse and keyboard) based on window messages.

Now I have come to implementing camera controls, and when I tried to rotate it I came across a problem. I have made it so that when I hold down the right mousebutton I enable rotating, and moving the mouse then rotates the camera based on how far the mouse-cursor has traveled since the last frame (pixels). Moving the mouse in either the horizontal or vertical direction alone creates no problem, but as soon as I do a circle-movement with the mouse, the camera starts spinning. So for a reason I don't know I get kind of a "rolling" of the camera in that situation. Does anyone have an idea why this is happening ?

The viewmatrix is being bult like this:

View = XMMatrixLookAtLH( EyePos, Focus, UpDir );


Update function of the camera, is being called every frame.

void Camera::Update()
{
if( fwd )
Forward();

if( back )
Backwards();

if( left )
Left();

if( right )
Right();

if( rotate )
{
Rotate();
View *= RotationX;
View *= RotationY;
}

cb.mView = XMMatrixTranspose( View );
m_pImmediateContext->UpdateSubresource( pConstantBuffer, 0, NULL, &cb, 0, 0 );
}



function that does the rotating, GetMouseDelta() returns how far the mouse has traveled since the last frame

void Camera::Rotate()
{
RotationX = XMMatrixRotationAxis( XMVectorSet( 1.0f, 0.0f, 0.0f, 0.0f ), -(float)pInput->GetMouseDelta().y*0.001f );
RotationY = XMMatrixRotationAxis( XMVectorSet( 0.0f, 1.0f, 0.0f, 0.0f ), -(float)pInput->GetMouseDelta().x*0.001f );
}

Edited by moodiez

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Your problem is probably caused by the order of transformations. First of, do you want to yield in a look-around rotation, in an orbiting around the focused object, or else (least probable) a rotation around the global origin? When rotation is applied, should it be done w.r.t. to some local or some global axes (I mean is it really yaw/pitch or do you want to spin around the global up direction regardless of any pitch)?

You further have to clarify whether you use row or column vectors. AFAIK the XMMatrixLookAtLH returns a row vector matrix. Then you multiply View with the incremental rotations you do it in an order that seems me odd. Then you're applying a XMMatrixTranspose onto the view matrix before transporting it to the shader script. I'm not familiar with D3D so my question is w.r.t. the transpose: Is this needed for the CBuffer and/or the shader script, or what is the reason for this?

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Hi haegarr.

To answer your questions, I want to rotate the camera around its local axes, not around any other object or global axes. I want to create a "camera" which I can rotate around itself and later on impement to manipulate its position in world space.

The way I rotate the view at the moment works fine, as long as I only rotate it around ONE axis.

The transposing is needed to update the data-structure thats being passed ot the shader (world,view,projection matrices)

Thanks in advance for further help :)

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You must be aware that rotating around the x axis followed by rotating around the y axis is different from rotating around the y axis followed by rotating around the x axis. Hence, if you push the mouse 10 units to the right and then 10 unit upwards, the result will differ from pushing the mouse 10 units upwards and then 10 units to the right. If you move the mouse more or less diagonally and do so with relatively high speed, the result will differ from a movement in the same direction but with significantly lower speed. This is because in the first case you do e.g.

Ry(45°) * Rx(45°)

while in the latter case you do (assuming 1/3 of speed with 3 samples in time)

Ry(15°) * Rx(15°) * Ry(15°) * Rx(15°) * Ry(15°) * Rx(15°)

Notice that the above shows what is called incremental rotation, especially if the angles get really small. The smaller the angles the more independent the rotation. However, you cannot process with arbitrarily high speed, and you will not enforce the user to move the mouse really slowly.

When you look at your current solution you'll see that the axis of rotation is orthogonal to the direction of mouse movement: horizontal movement = upwards directed axis of rotation; vertical movement = sidewards directed axis of rotation. Generalizing this means that however the mouse is moved, the axis of rotation is the perpDot of the movement direction. It is perhaps worth a try (I'm not 100% sure of the success, though).

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