glfreak

04-25-2008, 10:01 AM

Just wondering if the 3d acceleration hw is tied to a specific coordinate system, LHS or RHS? Does that matter?

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glfreak

04-25-2008, 10:01 AM

Just wondering if the 3d acceleration hw is tied to a specific coordinate system, LHS or RHS? Does that matter?

ZbuffeR

04-25-2008, 10:15 AM

no, and no.

overlay

04-25-2008, 10:48 AM

Here are two sections of the OpenGL 2.1 spec to take into account:

#1. section 2.11.2 "Matrices" page 45, comment about Rotate():

"

The computed matrix is a counter-clockwise rotation about the line through the origin with the specified axis when that axis is pointing up (i.e. the right-hand rule determines the sense of the rotation angle)."

"

#2. Appendix B "Corollaries", page 309, item 15:

"

15. OpenGL does not force left- or right-handedness on any of its coordinates systems. Consider, however, the following conditions:

(1) the object coordinate system is right-handed;

(2) the only commands used to manipulate the model-view matrix re Scale (with positive scaling values only), Rotate, and Translate;

(3) exactly one of either Frustum or Ortho is used to set the projection matrix;

(4) the near value is less than the far value for DepthRange.

If these conditions are all satisfied, then the eye coordinate system is right-handed and the clip, normalized device, and window coordinate systems are left-handed.

"

#1. section 2.11.2 "Matrices" page 45, comment about Rotate():

"

The computed matrix is a counter-clockwise rotation about the line through the origin with the specified axis when that axis is pointing up (i.e. the right-hand rule determines the sense of the rotation angle)."

"

#2. Appendix B "Corollaries", page 309, item 15:

"

15. OpenGL does not force left- or right-handedness on any of its coordinates systems. Consider, however, the following conditions:

(1) the object coordinate system is right-handed;

(2) the only commands used to manipulate the model-view matrix re Scale (with positive scaling values only), Rotate, and Translate;

(3) exactly one of either Frustum or Ortho is used to set the projection matrix;

(4) the near value is less than the far value for DepthRange.

If these conditions are all satisfied, then the eye coordinate system is right-handed and the clip, normalized device, and window coordinate systems are left-handed.

"

glfreak

04-25-2008, 12:05 PM

ZbuffeR, simple understandable answer. But why? is it because all coord-sys related stuff are handled in software, at matrix level? that we specify the matrix? what about backface culling that may be implemented early before rasterization stage? what about clip coordinates, would not be flipped for the 2 different systems?

Dark Photon

04-25-2008, 04:50 PM

ZbuffeR, simple understandable answer. But why? is it because all coord-sys related stuff are handled in software, at matrix level? that we specify the matrix? what about backface culling that may be implemented early before rasterization stage? what about clip coordinates, would not be flipped for the 2 different systems?

See the first post by "weary" here (http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=235892&SiteID=1).

The posts above and below it will give you more insight.

See the first post by "weary" here (http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=235892&SiteID=1).

The posts above and below it will give you more insight.

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