You have to project 3D coordinates (model view) back to 2D coordinates (LCD screen). I wrote an app that needed to do the exact opposite (2d coords to 3d coord and vectors). But the idea is the same.
3D coords --Model View--> 2D coord --Project View--> 2D screen coords gluProject takes care of the "--Model View--> 2D coord --Project View-- >" for you. It's quite a bit of math and such. You have to draw it out and get a good understanding of it. The hints i gave you above should give you a good direction (gluProject for mapping 3D to 2D; MatrixTrackerGL for obtaining the current model view and projection view matrices). The rest of the math you have to code yourself. Learn up on geometric calculations a bit, google a lot (that's what i did :-)). On Apr 3, 2:17 pm, William <william.caine...@gmail.com> wrote: > I am still lost. I am very new to opengl. I looked at the code and > there is a lot going on. And even if I can understand it, I still > have to then make code to do the detection. Someone has had to have > this problem in the past that I could see the actual code that does > the detection. > > On Apr 3, 11:55 am, Streets Of Boston <flyingdutc...@gmail.com> wrote: > > > > > - Get your objects coordinates in the model view (you should have > > those :)) > > - Get the current model view matrix (see MatrixTrackingGL class in > > your APIDemo's source code for OpenGL) > > - Take a look the gluUnProject/gluProject methods and use them to > > figure out what part of the LCD-screen your 3D objects are occupying. > > > On Apr 3, 10:24 am, William <william.caine...@gmail.com> wrote: > > > > //i rotate the cube using the following > > > //xRot,yRot are inc or decremented to change angles > > > gl.glRotatef(xRot, 1.0f, 0.0f, 0.0f); > > > gl.glRotatef(yRot, 0.0f, 1.0f, 0.0f); > > > > So yes i have access to yRot and xRot but they numbers range from -900 > > > to +900. I figure I can used them somehow to tell what is rotated but > > > I am unsure how. i just pass them in and it magically rotates for > > > me. so i am unsure how to tell from the numbers what angle the cube > > > is at. > > > > can I take a trig function to them or what? or do i take the xRot % > > > 360 and the remainder is what degree I am at. Or is xRot in radians > > > so I must convert it. > > > > On Apr 3, 12:41 am, Marco Nelissen <marc...@android.com> wrote: > > > > > Since you're rotating and drawing the cube, shouldn't you have that > > > > information in your app already? > > > > > On Thu, Apr 2, 2009 at 7:30 PM, William <william.caine...@gmail.com> > > > > wrote: > > > > > > Hi Folks, > > > > > > I am drawing and rotating a cube. Is there a programmatic way to tell > > > > > what side of the cube is facing me? > > > > > > For example if I randomly spin the cube when done spinning. I want to > > > > > know which face(s) I am looking at. 10% of face 1, 90% of face 2.- > > > > > Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
