# 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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OpenGL modelview matrix should be the DX transposed...

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Quote:
 Original post by blizzard999OpenGL 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 MikeMJHI 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 blizzard999OpenGL 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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translation matrix

DX1 0 0 x   0 1 0 y   0 0 1 z   0 0 0 1GL1 0 0 0   0 1 0 0   0 0 1 0   x y z 1

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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 y0 0 1 z0 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 00 1 0 00 0 1 0x y z 1

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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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