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Normalized Device Co-ordinates to World Space

2 posts in this topic

I did write a wonderfully detailed post about my problem, then accidentally closed the tab. So this'll be a little more brief, but hopefully still detailed enough to get some help!

Anyway, I'm trying to convert mouse co-ordinates to world space. At the moment, I'm passing in two normalized device co-ordinates, (x,y,-1.0f) and (x,y,1.0f), then transforming them by the inverse of (proj_matrix*view_matrix). I'm expecting to get two points - one on the near clipping plane and one on the far clipping plane, but I'm not. The near plane is 30, and the far plane is 5000, but I'm getting z values of 0.7 and 7 respectively.

I'm not doing any multiplication by any w value to get to clipping space - could that be the problem? If so, how should I get the w value to multiply all the elements by?

Here's the bits of my code that are relevant:

[code]Ray newray(0.2f,-0.2f,-1.0f,0.2f,-0.2f,1.0f);

[code]class Ray
cml::matrix44f_c inv_mat_;
vector3f start_, end_;

vector3f transformed_start_, transformed_end_;
Ray(float sx, float sy, float sz, float dx, float dy, float dz);
void SetRayEnds(float sx, float sy, float sz, float dx, float dy, float dz);

void SetMatrices(const cml::matrix44f_c & proj, const cml::matrix44f_c & view);
void Calculate();

vector3f GetYIntersection(float y);

[code]Ray::Ray(float sx, float sy, float sz, float dx, float dy, float dz) :

void Ray::SetRayEnds(float sx, float sy, float sz, float dx, float dy, float dz)

void Ray::SetMatrices(const cml::matrix44f_c & proj, const cml::matrix44f_c & view)
inv_mat_ = cml::inverse(proj*view);

void Ray::Calculate()
transformed_start_ = cml::transform_point(inv_mat_, start_);
transformed_end_ = cml::transform_point(inv_mat_, end_);

To all the matrix and graphics wizards, what am I doing wrong? Is this the way that you would approach the problem?

Thanks for your help!

EDIT: World space, not eye space. Edited by LordSputnik

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Very sorry, I did mean world space - it was late and I was sleepy!

The only thing I can think it could be is the cml::transform_point function I'm using - I've assumed that this multiplies the input point by the matrix as gluUnProject does, but that might not be right. I'll try making a 4x1 matrix containing the values plus the 1 at the bottom, and use straightforward matrix multiplication.

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