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

[Kevin Fishburne]

On 05/27/2012 02:14 AM, Kevin Fishburne wrote:
> On 05/26/2012 01:17 PM, tommyline at ...2340... wrote:
>> Oooooops!
>>
>> I just realized, you use Gl.Ortho mode. That means Glu.LookAt is not for you, I spent few hours trying to figure out how to make it work in ortho, but I can't. It behaves like mad, no matter what origin you set up. Sorry, that's one of the reasons I use perspective mode. I suppose the rotation in 2D is made by rotating world's vertexes, rather than camera, but I can be wrong.
>> Sorry for misunderstending you.
>>
>> Tomek
>>
>
> That's it man, now I'm finding out where you live and leaving a bag of
> rotten shrimp in your mailbox. ;)
>
> Alright, I'm done with ortho for now and have switched to perspective.
> Amazingly it worked nearly perfectly on the first attempt but one weird
> thing is happening:
>
>     UpVec1 = Sin(Rad(Camera.Orientation))
>     UpVec2 = Cos(Rad(Camera.Orientation))
>     UpVec3 = 0
>
>     Gl.MatrixMode(Gl.PROJECTION)
>     Gl.LoadIdentity()
>     Glu.Perspective(45, sWidth / sHeight, -1, 1)
>
>     Gl.MatrixMode(Gl.MODELVIEW)
>     Gl.LoadIdentity()
>
>     Glu.LookAt(Camera.WorldX, Camera.WorldY, 10, Camera.WorldX,
> Camera.WorldY, 0, UpVec1, UpVec2, UpVec3)
>
> It appears as though the scene is being rendered vertically inverted,
> like taking a screenshot and flipping it vertically in GIMP. Moving
> left/right works but moving up/down is backward. I tried experimenting
> with the up vector and eye/center Z parameters for Glu.LookAt with no
> success. I'll continue researching and experimenting but throw me a bone
> if you've seen this before.
>

I'll be damned. I think I got it. Looks like applying a certain scale 
transformation to the projection matrix does it:

   Gl.MatrixMode(Gl.PROJECTION)
   Gl.LoadIdentity()
   Glu.Perspective(45, sWidth / sHeight, -1, 1)
   Gl.Scalef(1, -1, 1)

Thanks for all your help. Hopefully I can move forward with this under 
my own power and not have to bother the list again for a while.

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