# OpenGL Cylinder Between Points

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I have been trying for a while to get a simple scene with two DirectX spheres at arbritrary positions and have a cylinder connect them. I have found some guides online that do it with OpenGL but when I attempt to recreate that with DirectX I can not produce the same result. I am trying to do this with Direct3D 9.

Does any one have a piece of code that creates two spheres and draws a cylinder betwen them?

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I have been trying for a while to get a simple scene with two DirectX spheres at arbritrary positions and have a cylinder connect them. I have found some guides online that do it with OpenGL but when I attempt to recreate that with DirectX I can not produce the same result. I am trying to do this with Direct3D 9.

Does any one have a piece of code that creates two spheres and draws a cylinder betwen them?

Can you post some code and show us where you are having trouble? I think that will be more instructive than just providing the code to you.

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Here is the current code as it stands. Anything in the tqd namespace is my math library that works correctly in OpenGL and from what I understand DirectX uses a transpose of OpenGL matricies.

 D3DXMATRIX matDGTrans, matDGScale, matDGlobal; D3DXMatrixScaling( &matDGScale, 0.25f, 0.25f, 0.25f ); D3DXMatrixTranslation( &matDGTrans, 0.0, 0.0f, 3.0f ); matDGlobal = matDGScale * matDGTrans; LPD3DXMESH atoma; D3DXCreateSphere( mDevice, 1.0f, 16, 16, &atoma, 0 ); { D3DXMATRIX matT, matS, matE; matT = D3DXMATRIX( tqd::Math::Matrix4f::TranslationMatrix( tqd::Math::Vector3f( -1.0f, 0.0f, 0.0f ) ).Transpose().Data() ); matS = D3DXMATRIX( tqd::Math::Matrix4f::ScaleMatrix( tqd::Math::Vector3f::One() * 0.25 ).Transpose().Data() ); matE = matDGlobal * matS * matT;// * matT * matR * matS; mDevice->SetTransform( D3DTS_WORLD, &matE ); // Draw atoma->DrawSubset( 0 ); } atoma->Release(); LPD3DXMESH atomb; D3DXCreateSphere( mDevice, 1.0f, 16, 16, &atomb, 0 ); { D3DXMATRIX matT, matS, matE; matT = D3DXMATRIX( tqd::Math::Matrix4f::TranslationMatrix( tqd::Math::Vector3f( 1.0f, 0.0f, 0.0f ) ).Transpose().Data() ); matS = D3DXMATRIX( tqd::Math::Matrix4f::ScaleMatrix( tqd::Math::Vector3f::One() * 0.25 ).Transpose().Data() ); matE = matDGlobal * matS * matT;// * matT * matR * matS; mDevice->SetTransform( D3DTS_WORLD, &matE ); // Draw atomb->DrawSubset( 0 ); } atomb->Release(); LPD3DXMESH bond; D3DXCreateCylinder( mDevice, 1.0f, 1.0f, 1.0f, 16, 16, &bond, 0 ); { const tqd::Math::Vector3f aPos = tqd::Math::Vector3f( -1.0f, 0.0f, 0.0f ); const tqd::Math::Vector3f bPos = tqd::Math::Vector3f( 1.0f, 0.0f, 0.0f ); tqd::Math::Vector3f vDiff = bPos - aPos; float length = vDiff.Magnitude(); tqd::Math::Angle angle( std::acos( vDiff.z() / length ), tqd::Math::Angle::Radian ); if( vDiff.z() < 0.00001f || vDiff.z() > -0.00001f ) vDiff.z() = 0.00001f; std::cout << vDiff << std::endl; if( vDiff.z() < 0.0f ){ vDiff.z() = -vDiff.z(); } tqd::Math::Vector3f axis( -vDiff.y() * vDiff.z(), vDiff.x() * vDiff.z(), 0.0f ); D3DXMATRIX matT, matS, matR, matE; matT = D3DXMATRIX( tqd::Math::Matrix4f::TranslationMatrix( aPos ).Transpose().Data() ); matS = D3DXMATRIX( tqd::Math::Matrix4f::ScaleMatrix( tqd::Math::Vector3f( 0.075f, 0.075f, length ) ).Transpose().Data() ); matR = D3DXMATRIX( tqd::Math::Matrix4f::RotationMatrix( angle, axis ).Transpose().Data() ); matE = matDGlobal * matT * matR;// * matT * matR * matS; mDevice->SetTransform( D3DTS_WORLD, &matE ); // Draw bond->DrawSubset( 0 ); } bond->Release(); 

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Can you describe the error that you are getting, or provide screenshots?

Also, have you tried using the XnaMath or DirectX math libraries to see if there is an error in translation between yours and what DirectX expects?

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tqd::Math::Matrix4f::TranslationMatrix ?!? Ahhh!!!! I need to translate, but . . I cant remember where the translation code is, which namespace was it in?

Post some pictures of your problem. Is tqd your library? Just wondering

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The error is that I am getting the two spheres being drawn where i expect them but the cylinder looks to be in the right place in the centre but is very small.
With the OpenGL code I do the following: I Translate to one of the spheres, Rotate to face the other and then scale the object.
When I try to do that with this it does not draw correctly.

I have tested the outputs of all of my matrix code against an equivilent DirectX function and they are all the same.

I will provide screenshots later, I am currently on the wrong OS and am backing up some files.

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tqd::Math::Matrix4f::TranslationMatrix ?!? Ahhh!!!! I need to translate, but . . I cant remember where the translation code is, which namespace was it in?

The call is a static function within a class in the tqd::Math namespace.
I agree it looks long but the verbosity is normally hidden by namespace renaming or using statements.

This code is from a library I have built up of bits of code I use for different things.

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I am pretty sure that DirectX matrices multiply in the order in which the transformations are applied (row-major operator on the right,), so you might want to make sure you are creating the expected transformation matrices. You might also want to try ditching the global transformation and using only local transformations until you get expected behavior so that your math is a bit easier to check by hand.

Edit: Yeah, Here

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Ok, I have some pictures.

What it should look like: [attachment=4158:OpenGL.png]
What it looks like: [attachment=4157:DirectX.png]

These two both use the same transformations for all objects.

I also changed the matrix code to use D3DXMatrixMultiply instead of operators.

The perspectives are different as the directx code is a plugin to another system and I have no control over the perspective but they should still look the same,

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Yeah, your transformations are jacked, and looking at your code, I don't believe you are performing the matrix multiplications in the right order. A global transform should be last, and they should usually look like this: local(scale -> rotation -> translation) -> global (assuming simple transformations)

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