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directxdirectx-11perspectivecameraprojection-matrixassimp

Perspective projection seems wrong, closer parts of a model appear smaller and vice versa

I'm trying out D3D11 and struggling to render a model correctly.

Here's my problem; while my world and view transformations seem right,
my perspective transformation seems to be wrong.
When I first rendered a model, something felt wrong, so I tried rotating the model to see what it was.
Then I noticed that, parts of the model closer to the camera appears smaller, and further parts appear larger.

If it's relevant, I'm using assimp to load my model, and here's how I do it.

mScene = aiImportFile(filename.c_str(), aiProcessPreset_TargetRealtime_MaxQuality | aiProcess_GenSmoothNormals | aiProcess_ConvertToLeftHanded | aiProcess_TransformUVCoords);

And here's how I build my projection matrix.

mProjection = XMMatrixPerspectiveFovLH(XMConvertToRadians(45.0f), 800.0f / 600.0f, -1.0f, 1.0f);

I fiddled with nearZ and farZ arguments of XMMatrixPerspectiveFovLH.
I tried increasing farZ gradually every frame, and then realized that as the value increases, the far clipping plane comes closer and closer to the camera, which is exactly the opposite of what I thought would happen.

In vertex shader, here's what I'm doing with vertex positions. It's pretty basic.

Out.Position = mul(mul(mul(position, World), CameraView), CameraProjection);

The model renders correctly in terms of position, scaling, rotation, and view-position.
So I'm assuming that world and view transforms are fine, and the problem is about the projection matrix.
To summarize, I'm thinking that Z values of projected vertices are, somehow, "flipped".

I google-searched many many times to no avail.

If someone could point out what I could be doing wrong, it would be very much appreciated.
If you need to see some of my code to help, please tell me.

Solution

  • Your near and far plane distances should be positive.

    Use something like:

    mProjection = XMMatrixPerspectiveFovLH(XMConvertToRadians(45.0f), 800.0f / 600.0f, 0.1f, 10.0f);

    I'll make a note to consider adding assert( NearZ > 0.f); assert( NearZ < FarZ ); to those DirectXMath functions and make sure that's explicit in the docs. distance means positive number here.

    PS: You should take a look at DirectX Tool Kit