How to get depth of vertex in 0 - 1 range

Question

I want to get the depth of vertex in 0 to 1 range(like it done in the shader) and I do it like this

    D3DXVec3TransformCoord(&vertex, &vertex, &wvp);

depth = vertex.z;

It works(sometimes wrong) but when I write This

    if (depth > 1.0f || depth < 0.0f)return false;

Sometimes it returns false. How can I get correct depth for vertex in 0 to 1 range??

I want to compare two vertexes and select the nearest

EDIT

    wvp = worldmatrix*viewmatrix*projectionmatrix;

It works wrong when I zoom in

Then in whít order do you multiply together the model, view and projection matrices — Bálint, Feb 09 '16 at 12:46
For x and y I know we have to divide by w to get them in normalized device coordinates, but I can't recall whether z is special in that regard. (This is usually the kind of thing I solve by trying it both ways and seeing whether one fixes it, rather than a first-principles mathematical derivation...) — DMGregory, Feb 09 '16 at 13:14
@Bálint The convention in D3DX is v*M. Do you have anything to back up your arbitrary swap of convention? — Lars Viklund, Feb 09 '16 at 13:33
Possible duplicate of When is the Z coordinate normalized in GLSL? — Tim, Feb 09 '16 at 14:12
If you want to compare two vertices and select the nearest, then you'll find it much easier (and faster) to just compare squared distance of each from the camera. — Maximus Minimus, May 28 '19 at 11:32

score 1 · Answer 1 · answered Dec 29 '18 at 03:24

You are missing the normalization step, which requires a W component.

Hence, you should be calling D3DXVec4Transform and not D3DXVec3TransformCoord.

You need to feed this your vertex, with the last component (W) set to a 1.0 value.

The output vertex will have W set in the last component, and you need to divide by that:

v_in[3] = 1.0;

D3DXVec4Transform
(
    &v_out,
    &v_in,
    &wvp
);

v_out[0] = v_out[0] / v_out[3];
v_out[1] = v_out[1] / v_out[3];
v_out[2] = v_out[2] / v_out[3];

Now you can use v_out[2] as the depth value, but beware: it ranges from -1 to 1, and not from 0 to 1 as you assumed.

score 0 · Answer 2 · answered Feb 09 '16 at 12:57

0

Matrix multiplication is not commutative. You need to do projection * view * model

answered Feb 09 '16 at 12:57

Bálint

14,887
2
34
55

No it also dont works – harut9 Feb 09 '16 at 13:06
Ok, try out something: before multiplying the vertex with the mvp matrix, multiply it with the mv matrix, and orint out the z value. – Bálint Feb 09 '16 at 13:07
I have already done like that – harut9 Feb 09 '16 at 13:25

How to get depth of vertex in 0 - 1 range

2 Answers2