Gimbal Lock?

Blitz3D Forums/Blitz3D Programming/Gimbal Lock?

Andy (Posted 2003) [#1]

I've always just worked around it by using turn entity instead of rotateentity, but as I am approaching a more serious stage in my projects evolution, I am wondering 'what am I missing'? I found the following code on http://www.dscho.co.uk/blitz/tutorials/quaternions.shtml I have changed it to use both rotateentity and turnentity. As far as I can see, using turnentity makes the 'Gimbal Lock' problem go away... Propably because B3D uses Quaternians internally. What am I missing? Why should I use quaternions when turnentity does the same... ; Set up the scene quickly Graphics3D 800,600 SetBuffer BackBuffer() cube = CreateExampleCube() cam = CreateCamera() TranslateEntity cam, -5, -5, -5 PointEntity cam, cube CameraViewport cam, 0, 0, GraphicsWidth (), GraphicsHeight () ; the start rotation Global pitch = 0 Global yaw = 0 Global roll = 0 Global test = 0 Global a$="" Repeat ; update the rotation pitch = pitch + KeyHit(200) * 10 ; up pitch = pitch - KeyHit(208) * 10 ; down yaw = yaw + KeyHit(203) * 10 ; left yaw = yaw - KeyHit(205) * 10 ; right roll = roll + KeyHit(30) * 10 ; a roll = roll - KeyHit(44) * 10 ; z If KeyHit(68) Then test=Abs(test-1) ; rotate the cube If test=0 Then ; Rotate using RotateEntity RotateEntity cube, pitch, yaw, roll, 1 a$="RotateEntity" EndIf If test=1 Then ; Rotate using TurnEntity RotateEntity cube, 0.0, 0.0, 0.0, 1 TurnEntity cube,pitch,0.0,0.0, 1 TurnEntity cube,0.0,yaw,0.0, 1 TurnEntity cube,0.0,0.0,roll, 1 a$="TurnEntity" EndIf ; draw the scene UpdateWorld RenderWorld Text 10, 10, "Pitch:" + Int(EntityPitch (cube)) Text 10, 20, "Yaw: " + Int(EntityYaw (cube)) Text 10, 30, "Roll: " + Int(EntityRoll (cube)) Text 10, 50, "Use cursor keys, a, z, F10 and escape to exit" Text 10, 60, a$ Flip 1 Until KeyHit(1) ; escape End Function CreateExampleCube() ; This will create & return a white cube with 3 coloured spikes going through it ; to emphasise the rotations, and also a light Local cube = CreateCube() Local xspike = CreateCone(16, True, cube) Local yspike = CreateCone(16, True, cube) Local zspike = CreateCone(16, True, cube) Local tempBrush = CreateBrush(255, 255, 255) PaintEntity cube, tempBrush BrushColor tempbrush, 255, 0, 0 PaintEntity xspike, tempBrush BrushColor tempbrush, 0, 255, 0 PaintEntity yspike, tempBrush BrushColor tempbrush, 0, 0, 255 PaintEntity zspike, tempBrush ScaleEntity xspike, 0.5, 4, 0.5 ScaleEntity yspike, 0.5, 4, 0.5 ScaleEntity zspike, 0.5, 4, 0.5 RotateEntity xspike, 0, 0, 0, 1 RotateEntity yspike, 90, 0, 0, 1 RotateEntity zspike, 0, 0, 90, 1 FreeBrush tempBrush Local light = CreateLight(1) PositionEntity light, -5, -5, -4 Return cube End Function Andy

FlameDuck (Posted 2003) [#2]

You're not missing anything. Blitz does use quaternions internally.

Andy (Posted 2003) [#3]

Thanks mate. Andy

Wavey (Posted 2003) [#4]

I would say the main use of the quaternion code is to interpolate between rotations: that gimbal lock disappears too is a bonus. The interpolation examples show that Blitz uses quaternions internally as well.