Question

I’m having problems creating a 3D first-person camera in DirectX 11.

I have a camera at (0, 0, -2) looking at (0, 0, 100). There is a box at (0, 0, 0) and the box is rendered correctly. See this image below:

When the position of the box (not the camera) changes, it is rendered correctly. For example, the next image shows the box at (1, 0, 0) and the camera still at (0, 0, -2):

However, as soon as the camera moves left or right, the box should go to the opposite direction, but it looks twisted instead. Here is an example when the camera is at (1, 0, -2) and looking at (1, 0, 100). The box is still at (0, 0, 0):

Here is how I set my camera:

// Set the world transformation matrix.

D3DXMATRIX rotationMatrix;          // A matrix to store the rotation information
D3DXMATRIX scalingMatrix;           // A matrix to store the scaling information
D3DXMATRIX translationMatrix;       // A matrix to store the translation information

D3DXMatrixIdentity(&translationMatrix);

// Make the scene being centered on the camera position.
D3DXMatrixTranslation(&translationMatrix, -camera.GetX(), -camera.GetY(), -camera.GetZ());

m_worldTransformationMatrix = translationMatrix;

// Set the view transformation matrix.

D3DXMatrixIdentity(&m_viewTransformationMatrix);

D3DXVECTOR3 cameraPosition(camera.GetX(), camera.GetY(), camera.GetZ());

// ------------------------
// Compute the lookAt position
// ------------------------

const FLOAT lookAtDistance = 100;

FLOAT lookAtXPosition = camera.GetX() + lookAtDistance * cos((FLOAT)D3DXToRadian(camera.GetXZAngle()));
FLOAT lookAtYPosition = camera.GetY() + lookAtDistance * sin((FLOAT)D3DXToRadian(camera.GetYZAngle()));
FLOAT lookAtZPosition = camera.GetZ() + lookAtDistance * (sin((FLOAT)D3DXToRadian(camera.GetXZAngle())) * cos((FLOAT)D3DXToRadian(camera.GetYZAngle())));

D3DXVECTOR3 lookAtPosition(lookAtXPosition, lookAtYPosition, lookAtZPosition);

D3DXVECTOR3 upDirection(0, 1, 0);

D3DXMatrixLookAtLH(&m_viewTransformationMatrix,
                   &cameraPosition,
                   &lookAtPosition,
                   &upDirection);

RECT windowDimensions = GetWindowDimensions();
FLOAT width = (FLOAT)(windowDimensions.right - windowDimensions.left);
FLOAT height = (FLOAT)(windowDimensions.bottom - windowDimensions.top);

// Set the projection matrix.

D3DXMatrixIdentity(&m_projectionMatrix);
D3DXMatrixPerspectiveFovLH(&m_projectionMatrix,
                           (FLOAT)(D3DXToRadian(45)),  // Horizontal field of view
                           width / height,    // Aspect ratio
                           1.0f,              // Near view-plane
                           100.0f);           // Far view-plane

Here is how the final matrix is set:

D3DXMATRIX finalMatrix = m_worldTransformationMatrix * m_viewTransformationMatrix * m_projectionMatrix;

// Set the new values for the constant buffer
mp_deviceContext->UpdateSubresource(mp_constantBuffer, 0, 0, &finalMatrix, 0, 0);

And finally, here is the vertex shader that uses the constant buffer:

VOut VShader(float4 position : POSITION, float4 color : COLOR, float2 texcoord : TEXCOORD)
{
    VOut output;

    output.color = color;
output.texcoord = texcoord;
output.position = mul(position, finalMatrix);  // Transform the vertex from 3D to 2D

    return output;
}

Do you see what I’m doing wrong? If you need more information on my code, feel free to ask: I really want this to work.

Thanks!

Answer 1

The problem is you are setting finalMatrix with a row major matrix, but HLSL expects a column major matrix. The solution is to use D3DXMatrixTranspose before updating the constants, or declare row_major in the HLSL file like this:

cbuffer ConstantBuffer
{
    row_major float4x4 finalMatrix;
}