I just started learning about Direct3D and 3D graphics in general. I was wondering why when you render something simple, like a triangle, you don't have to go through all the transformations in order to see in on the screen. That is, why don't you have to transform from local space->world space->view space->etc. It seems that direct3D already has a default state?

Yes I'm talking about a simple 2D triangle. I'm just confused on what happens when you give the coordinates for a triangle to Direct3D. How does Direct3D decide what part of the screen in visible?

This is from an example and it uses D3DFVF_XYZ. The only transformation the code performs is a projection using D3DXMatrixPerspectiveFovLH. Now since no view transformation was performed, where is "the camera" located, how does direct3d determine this?

As my opinion, use D3DXMatrixLookAtLH can create a matrix which transform the vertex from world space to view space,the D3DXMatrixPerspectiveFovLH will generate the matrix of 3d space to 2d Homogeneous Clip Space ,and the local space to world space matrix is just created by yourself.Last, the following operation will transform your 3d space vertex to 2d screan:

ProjectedVertex = your3Dvertex * ( WorldMatrix * ViewMatrix * ProjectionMatrix);

ScreenX= ProjectedVertex .x * ViewportWidth/2 + ViewportLeft + ViewportWidth / 2
ScreenY= -ProjectedVertex .y * ViewportHeight/2 + ViewportTop+ ViewportHeight/ 2

However ,D3D can handle these operation for you automaticly,you just simply inform d3d which type of matrix you want to specify by calling the "SetTransform" and put the correct parameter to it.