問題描述
如何圍繞其中心旋轉 3D 模型？ (How to rotate a 3D model around its center?)
I am making a 3d car game and I have a problem with rotation. I want to rotate a model around itself but when I move, it starts to move around the world !
The question is: How do I make a center for the model to move around?
I tried to change the code like this :
effect.World = Matrix.CreateRotationZ(modelRotation) * effect.World = Matrix.CreateTranslation(position);
now instead of moving forward relative to the model, orientation it moves in a set direction ! & this is my code:
effect.World = Matrix.CreateTranslation(position) * Matrix.CreateRotationZ(modelRotation);
effect.View = camera.View;
effect.Projection = camera.Projection;
參考解法
方法 1:
I have a few tips to get you started:
- Matrix multiplication order in DirectX/Xna is differrent than you learned in school.
In school v = A B y meant: v = A (B y). So when chaining matrices, B is applied first.
If you want to combine matrix A and B, you multiply them like C = A B
In Directx/XNA, the order is reversed. To combine matrix B and A, you write var C = B * A;
To stop me from making mistakes, I adopt a naming convention: each matrix (or transform) is called AtoB: WorldToView, ModelToWorld, or ModelToRotatedModel.
This reminds you that the output of the first matrix must match the input of the right matrix :
var modelToView = modelToWorld * worldToView;
and not:
var nowhereToNowhere = worldToView * modelToWorld;
This helped me a lot, I hope it helps you sort out your matrix problems.
P.S. I hope the origin of your car model is in the center of the car, otherwise the it will still move around strangely.
方法 2:
Try switching these values around:
effect.World = Matrix.CreateTranslation(position) * Matrix.CreateRotationZ(modelRotation);
so it becomes:
effect.World = Matrix.CreateRotationZ(modelRotation) * Matrix.CreateTranslation(position);
I follow a simple acronym thats called ISROT
Identity
Scale
Rotation
Orientation
Translation
You work right to left, so you always end your statement with Translation.
(by hakam、user180326、Neil Knight)