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OpenGL Modelview matrix

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Hi, I am implementing something in directx while using a openGL program as a reference and I came across a modelview matrix. I was just making sure this is the same as the view matrix in directx. The camera transformation matrix. Thanks, Chase

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With respect to DX i think the direct equivalent would be a 'view * world' matrix. I'm not too familiar with DX (worked with 7, 8 and very limited in 9) so someone correct me if i'm wrong.

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Quote:
Original post by blizzard999
OpenGL modelview matrix should be the DX transposed...


I don't think so. DirectX maintains a different concept than OpenGL--it has seperate World and View matrices, whereas OpenGL has a combined ModelView matrix. In this respect nts is correct.

It is true, however, that DirectX matrices' are column major (where OpenGL's are row-major by default).

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Quote:
Original post by MikeMJH
I don't think so. DirectX maintains a different concept than OpenGL--it has seperate World and View matrices, whereas OpenGL has a combined ModelView matrix. In this respect nts is correct.


You are right but...world and view matrices are not different concepts!

Nts is right too

[GL modelview] = transposed([DX view] * [DX world])

Load the same matrix and you get the same results.

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Quote:
Original post by MikeMJH
Quote:
Original post by blizzard999
OpenGL modelview matrix should be the DX transposed...


I don't think so. DirectX maintains a different concept than OpenGL--it has seperate World and View matrices, whereas OpenGL has a combined ModelView matrix. In this respect nts is correct.

It is true, however, that DirectX matrices' are column major (where OpenGL's are row-major by default).


Um matrices in Direct3D are row-major while matrices in OpenGL are column-major.

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From here:

Quote:
9.005 Are OpenGL matrices column-major or row-major?

For programming purposes, OpenGL matrices are 16-value arrays with base vectors laid out contiguously in memory. The translation components occupy the 13th, 14th, and 15th elements of the 16-element matrix.

Column-major versus row-major is purely a notational convention. Note that post-multiplying with column-major matrices produces the same result as pre-multiplying with row-major matrices. The OpenGL Specification and the OpenGL Reference Manual both use column-major notation. You can use any notation, as long as it's clearly stated.

Sadly, the use of column-major format in the spec and blue book has resulted in endless confusion in the OpenGL programming community. Column-major notation suggests that matrices are not laid out in memory as a programmer would expect.

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No sir thats not right. According to a very reliable source[MSDN] the translation matrix in OpenGL goes more like this :


| 1 0 0 x |
| 0 1 0 y |
| 0 0 1 z |
| 0 0 0 1 |




For Direct3D you'd have to transpose the above matrix into row-major.

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Instead of rating me down why don't you google it for yourself? Or visit MSDN.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/opengl/glfunc03_9a05.asp

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Original post by Khaosifix
No sir thats not right. According to a very reliable source[MSDN] the translation matrix in OpenGL goes more like this :


1 0 0 x
0 1 0 y
0 0 1 z
0 0 0 1




For Direct3D you'd have to transpose the above matrix into row-major.[/quote]

****************************************************************************

Instead of report me what MSDN says...try this


...
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(4,5,6);
float pf[16];
glGetFloatv(GL_MODELVIEW_MATRIX, pf);
...




Debug Output : pf[0], pf[1],...,pf[15]


1,0,0,0,0,1,0,0,0,0,1,0,4,5,6,1




That is


1 0 0 0
0 1 0 0
0 0 1 0
x y z 1




And please...check your assertions as I do when answer to someone :)

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Khaosifix's translation matrix is indeed right, heck if you want a more relieable source then check page 700 of the OpenGL Red Book (1.4 revision, so might be a different page in the free online one/earlier)

The only difference is in how you read the data out, you are reading its

pf[0] pf[1] pf[2] pf[3]
pf[4] pf[5] pf[6] pf[7]
pf[8] pf[9] pf[10] pf[11]
pf[12] pf[13] pf[14] pf[15]


which is infact the transpose, as OpenGL treats it as

pf[0] pf[4] pf[8] pf[12]
pf[1] pf[5] pf[9] pf[13]
pf[2] pf[6] pf[10] pf[14]
pf[3] pf[7] pf[11] pf[15]

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I presume that it is more important from a programmer point of view to know how a library stores data in memory (for example to implement a compatible matrix class).
From a math point of view there is no doubt that the common form is

1 0 0 x
0 1 0 y
0 0 1 z
0 0 0 1

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indeed, personally I find it easier to visualise the matrix as column major, it makes the maths easier to die the matrix positions together with the array access.

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Actually row-major is easier for me to understand and do math on. But I guess thats just me.

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I use OpenGL so I stored elements in this way so I have no need to transpose it.
It's not that problem: write once use forever...the only thing is: if you have to load a matrix it must be in the same form of the library.
When you have your matrix and vector classes you can forget about 'low' level problems...

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