[Gambas-user] gb3: OpenGL Rotate and Translate logic

[tommyline at ...2340...]

Hi Kevin.
I think you should concider using Glu.LookAt function, which should solve all your problems.

I used it in collision project (attached) to follow the ball.
You just set the camera with few parameters, and that's it! Please check the command help in Gambas.
Simply speaking, you define eye point's (x,y,z position - no need for scale or translate), point you look at and point where the top of camera is (by changing it, you rotate the world in front of you), so I think that would solve it. See the attached example to see how I did it. Press F3 to see how it works.

>From glu man pages:

NAME
	  gluLookAt - define a viewing transformation


     C SPECIFICATION
	  void gluLookAt( GLdouble eyeX,
			  GLdouble eyeY,
			  GLdouble eyeZ,
			  GLdouble centerX,
			  GLdouble centerY,
			  GLdouble centerZ,
			  GLdouble upX,
			  GLdouble upY,
			  GLdouble upZ )


     PARAMETERS
	  eyeX,	eyeY, eyeZ
			  Specifies the	position of the	eye point.

	  centerX, centerY, centerZ
			  Specifies the	position of the	reference
			  point.

	  upX, upY, upZ	  Specifies the	direction of the up vector.

     DESCRIPTION
	  gluLookAt creates a viewing matrix derived from an eye
	  point, a reference point indicating the center of the	scene,
	  and an UP vector.

	  The matrix maps the reference	point to the negative z	axis
	  and the eye point to the origin.  When a typical projection
	  matrix is used, the center of	the scene therefore maps to
	  the center of	the viewport.  Similarly, the direction
	  described by the UP vector projected onto the	viewing	plane
	  is mapped to the positive y axis so that it points upward in
	  the viewport.	 The UP	vector must not	be parallel to the
	  line of sight	from the eye point to the reference point.

	  Let

	      (	centerX	  -   eyeX  )
	  F = |			    |
	      |	centerY	  -   eyeY  |
	      (	centerZ	  -   eyeZ  )

	  Let UP be the	vector (upX,upY,upZ).

	  Then normalize as follows: f = _____
					 ||F||

	  UP' =	______
		||UP||

	  Finally, let s = f x UP', and	u = s x	f.

	  M is then constructed	as follows:
	      (	s[0]   s[1]   s[2]  0  )
	      |	u[0]   u[1]   u[2]  0  |
	  M = |			       |
	      |-f[0]  -f[1]  -f[2]  0  |
	      |	 0	0      0    1  |
	      (			       )
	  and gluLookAt	is equivalent to glMultMatrixf(M);
	  glTranslated (-eyex, -eyey, -eyez);

I hope I did help.

Tomek.



Hi Tomek. I'm not sure that saving and loading the matrix will do the 
trick, but I don't really understand the implications of doing so 
either. I basically want to translate, scale and rotate the matrix so 
that the camera is always at the center of the render window and I can 
draw objects using their native world coordinates. The camera is 
pointing straight down at the ground (perpendicular to the landscape). 
Rotating the camera/matrix will spin the landscape with the camera being 
the origin, just like spinning a globe of Earth if the camera is 
pointing down at the north pole. It would look something like this:

http://www.youtube.com/watch?v=mee_FiIQoEY

If I do this below everything is perfect (including zoom) but it has no 
rotation:

   ' Rotate, translate and scale matrix.
   ScreenOffsetX = sWidth / 2 / 128 / Zoom.Current
   ScreenOffsetY = sHeight / 2 / 128 / Zoom.Current
   Gl.LoadIdentity()
   Gl.Scalef(128 * Zoom.Current, 128 * Zoom.Current, 1)
   Gl.Translatef(- Camera.WorldX + ScreenOffsetX, - Camera.WorldY + 
ScreenOffsetY, 0)

Incorporating rotation rotates the scene but not around the camera. 
Using the above code and then rendering everything at its native world 
coordinates looks like this:

http://eightvirtues.com/sanctimonia/misc/Everything%20But%20Rotation.ogv

If necessary I can translate the matrix by (x,y) units which have been 
pre-rotated opposite the angle the matrix was rotated at. I can 
basically manually "undo" the matrix rotation if it needs to be 
translated post rotation, if that makes any sense. Some instinct inside 
me keeps nagging that I might need to do a trick like that to get it to 
work.

-- 
Kevin Fishburne
Eight Virtues
www: http://sales.eightvirtues.com
e-mail: sales at ...1887...
phone: (770) 853-6271


------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
_______________________________________________
Gambas-user mailing list
Gambas-user at lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/gambas-user
-------------- next part --------------
A non-text attachment was scrubbed...
Name: col1-0.0.3.tar.gz
Type: application/x-compressed-tar
Size: 164859 bytes
Desc: not available
URL: <http://lists.gambas-basic.org/pipermail/user/attachments/20120524/5212e17d/attachment.bin>