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VR & TRANSF

VR & TRANSF. Glenn G. Chappell CHAPPELLG@member.ams.org U. of Alaska Fairbanks CS 481/681 Lecture Notes Monday, February 23, 2004. Review: Writing VR Juggler App’s [1/2]. For our VR programming, we are using a library called VR Juggler . Free & open-source.

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VR & TRANSF

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  1. VR & TRANSF Glenn G. ChappellCHAPPELLG@member.ams.org U. of Alaska Fairbanks CS 481/681 Lecture Notes Monday, February 23, 2004

  2. Review:Writing VR Juggler App’s [1/2] • For our VR programming, we are using a library called VR Juggler. • Free & open-source. • Developed at VRAC, Iowa State U. • C++ • Not hardware- or OS-specific. • Run it on your own computer. • The functionality provided by VRJ is roughly the same as that of all major VR library: • Manages windows, contexts, threads, hardware configuration (including stereo/mono). • Interface to VR input devices. • Sets up projection matrices based on user’s position. • Calls user code for display, etc. CS 481/681

  3. Review:Writing VR Juggler App’s [2/2] • We write a VR JugglerApplication. • This is a C++ object. • Callbacks are public member functions. • Execution is multithreaded, synchronized according to “frames”. • All threads have the same static & dynamic memory spaces. • Watch out for conflicts! • See simpleApp for an example. Start of Frame preFrame intraFrame draw draw postFrame End of Frame CS 481/681

  4. Review:Discovery Lab Training • All CS 481/681 students get “Discovery Lab Operator” status. • Access to lab. • Accounts on ARSC SGI’s, including igie. • Can bring guests. • Drinks not allowed near console & screens. • When you use the lab, you are responsible for keeping it clean and not misusing the equipment. • When you leave the DLab: • Log out. • If no one else is there: • Plug the driver glasses & wand into their chargers. • Mute the audio. • Turn off the projectors. • Log out of the touch panel. • Dim the lights. • Make sure the doors are fully closed. CS 481/681

  5. VR & TRANSF:Flying [1/3] • Write a (desktop) flyer that uses a variable of type transf to hold the viewing transformation. • Use tfogl.h where is it convenient. • See tffly.cpp, on the web page. • The following slides contain some of the relevant ideas. CS 481/681

  6. VR & TRANSF:Flying [2/3] • Storing the Viewing Transformation • Define a global of type transf; this does everything a plane/spaceship can do. transf viewtf; • Using the Viewing Transformation • In the display function: glPushMatrix(); glTransform(viewtf); // Uses tfogl.h … // Draw transformed objects glPopMatrix(); • Initializing the Viewing Transformation viewtf = transf(vec(0., 0., -3.)); // In function init? • Type vec represents a translation. Convert to transf so the assignment works. CS 481/681

  7. VR & TRANSF:Flying [3/3] • Changing the Viewing Transformation • Save the mouse position & button states where appropriate. • Use these to modify viewtf in the idle function. • Generally: transf newtf = …; viewtf = compose(newtf, viewtf); glutPostRedisplay(); • Equivalent forms of the middle line: viewtf = newtf.compose(viewtf); viewtf = viewtf.lcompose(newtf); // lcompose: l = left viewtf.lcompose_assign(newtf); • The last two are like * and *=. CS 481/681

  8. VR & TRANSF:Moving with the Wand • In terms of transformations, one of the trickier parts of VR is moving objects together in an arbitrary frame of reference. • For example, moving an object with the wand. • To draw an object in the wand’s frame of reference: glPushMatrix(); glTransform(myUser.getTransf(USR_WAND)); … // Draw transformed objects glPopMatrix(); CS 481/681

  9. VR & TRANSF:Where is the Wand Pointing? • To find where the wand points: vec wandDir = myUser.getFrontVec(USR_WAND); • How do we turn this into a 2-D vector (no up/down)? • Solution 1: wandDir[1] = 0.; wandDir = wandDir.normalized(); • Solution 2: wandDir -= wandDir.component(vec(0.,1.,0.)); wandDir = wandDir.normalized(); CS 481/681

  10. VR & TRANSF:Harder Problems • How do we grab a stationary object with the wand? • Always grab the “right” object. • No “popping” into place? • How do we create a usable “flying” interface for the CAVE? • What about “walking”? CS 481/681

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