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Right Setup for Drawing?


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#1 Sim   Members   -  Reputation: 122

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Posted 06 November 2001 - 08:47 AM

Hello! I''m currently coding an 3d presentation engine, which load all parameters from a special file including some nicely interpolated keyframes and links to an unlimited amount of 3D Models. I''ve designed like Flash, so all keyframes are stored in a timeline, the objects have no properties like position,rotation ect. It looks like this: Engine-> Scene-> Timeline(has all animation data) 3DModel1 3DModel2 ParticleEmmitter1 .... Now I have A Problem, if I just change only the position OR the the rotation OR the scaling, it looks nicely. But if I change by example the position and the scaling, the objects get other positions: glTranslate(1.0,1.0,0.0); == Translation to 1,1,0 BUT: glTranslate(1.0,1.0,0.0); glScale(0.5,0.5,0.5); == Translation to 0.5,0.5,0 And If you combine the whole thing with glRotate it ends up in a nightmare. I just want to rotate/scale the graphic objects attached to the timeline, but there position in worldspace shoudn''t be altered by the Rotation/Scaling. I hope you understand my problem, I think I have to include some tricky use of glPush/Pop but I don''t know how and I''m running out of time, otherwise I could implement a Matrixclass, but for now I need a simple and fast solution THANKS ALOT! PS: This is my Timeline::OnDraw() Function, which is called BEFORE the other objects are drawn: glLoadIdentity(); CVector3 CameraPos = ((CCamera *)Parent()->Child())->Location; CVector3 CameraRot = ((CCamera *)Parent()->Child())->Rotation; if (active) // If The Timeline Is Running { if (currentkey < number_of_keyframes) currentkey++; //If There Are Other Frames Waiting else if(repeat) currentkey = 0; } //Camera glTranslatef(-CameraPos.GetX(), -CameraPos.GetZ(), -CameraPos.GetY()); glRotatef(CameraRot.GetX(),1.0f,0,0); glRotatef((float)360.0 - CameraRot.GetY(),0,1.0f,0); //Timeline glRotatef(pKeyFrame[currentkey].Rotation.GetX(), 1.0, 0.0, 0.0); glRotatef(pKeyFrame[currentkey].Rotation.GetY(), 0.0, 1.0, 0.0); glRotatef(pKeyFrame[currentkey].Rotation.GetZ(), 0.0, 0.0, 1.0); glTranslatef(pKeyFrame[currentkey].Position.GetX(),pKeyFrame[currentkey].Position.GetY(),pKeyFrame[currentkey].Position.GetZ()); glScalef(pKeyFrame[currentkey].Scaling.GetX(),pKeyFrame[currentkey].Scaling.GetY(),pKeyFrame[currentkey].Scaling.GetZ()); Material = pKeyFrame[currentkey].Material; GiveToChildren(); THANKS ONCE AGAIN!

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#2 zedzeek   Members   -  Reputation: 528

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Posted 06 November 2001 - 09:31 AM

check out some site on linear algebra or better yet get a book out of the library about it itll explain everything better.
but basically any operations (translate,rotate,scale) happen on the current matrix if u use glLoadIdentity() this is the identity matrix located at (0,0,0) in world space thus any rotate call u make after that will rotate around that point (0,0,0) if u go translate(1,0,0) + then do a rotate the rotation will occur around worldspace position(1,0,0).
what u want to do is rotate/scale around the objects center right?
well translate the object until its at (0,0,0) do the rotation/scaling and then translate back

#3 Sim   Members   -  Reputation: 122

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Posted 06 November 2001 - 10:01 AM

you mean I should first rotate translate the camera, then translate back to origin rotate/scale and then translate to
current position of the 3DModel/Particle/whatever.
There is just one thing I don''t understand, when do I have to
draw the object, at the end of whole process or somewhere between

Thanks

#4 Sim   Members   -  Reputation: 122

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Posted 07 November 2001 - 03:47 AM

Help!!

I can''t get it working.
Perhabs I should explain it in more detail:

I want to rotate the object:
at 0,0,0 I call glRotate.
then I glTranslate to the position.
then I draw it.

BUT if I rotate lets say 90 deg around the x-axis, and then
translate to lets say 10,20,0, it will end up somewhere else
in worldspace.

My Question is How can do a Rotation in Localspace only, while
the translation in worldspace is not affected?

To the Point, the model should always be by example at 10,10,20
(worldspace), while the rotation can be completly different.

THANKS




#5 Scarab0   Members   -  Reputation: 122

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Posted 07 November 2001 - 04:53 AM

Have you tried reversing the operation? Ie, glTranslate and than glRotate.

#6 Sim   Members   -  Reputation: 122

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Posted 07 November 2001 - 06:20 AM

THAT''S IT!
a simple reverse does it!
THANKS ALOT!!!!!!




#7 Scarab0   Members   -  Reputation: 122

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Posted 09 November 2001 - 06:51 AM

Hey that''s what the forums are for, right?




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