electronic visualization laboratory, university of illinois at chicago stereoscopic computer...

electronic visualization laboratory, university of illinois at chicago

Stereoscopic Computer Graphics

CS426Jason Leigh

© 2004-2012Electronic Visualization Laboratory


• 4-10% of population cannot see stereopsis.

• Other cues come into play to provide sense of depth.

• Try to take advantage of those in addition to stereopsis for best results.


Depth CuesPerceiving “depth” with one eye closed

• Perspective.Objects get smaller the further away they are and parallel line converge in distance.

• Sizes of known objects.We expect certain object to be smaller than others. If an elephant and a tea cup appear the same size then we expect the elephant to be further away.

• Detail.Close objects appear in more detail, distant objects less.

• Occlusion.An object that blocks another is assumed to be in the foreground.

• Lighting, shadows.Closer objects are brighter, distant ones dimmer. There a number of other more subtle cues implied by lighting, the way a curved surface reflects light suggests the rate of curvature, shadows are a form of occlusion.

• Relative motion.Objects further away seem to move more slowly than objects in the foreground.


Using both eyes

• Binocular disparity.This is the difference in the images projected onto the back of the eye (and then onto the visual cortex) because the eyes are separated horizontally by the interocular distance.

• Only good to about 15-20 feet. • Accommodation.

This is the muscle tension needed to change the focal length of the eye lens in order to focus at a particular depth.

• Convergence.This is the muscle tension required to rotate each eye so that it is facing the focal point.

• For STEREOSCOPIC Computer Graphics the “3D” effect is achieved through Binocular Disparity.


Ways of Seeing Stereoscopic Content


Free Viewing

In general you are creating 2 views (one for each eye).This means your graphics card needs to render the scene twice.


Anaglyphic Stereo


Stereoscopes


CAVE - 1992

Active Stereo LCD Shutter glassesUniversity of Illinois at Chicago


GeoWall - 2001


Varrier - 2005


Cyber-Commons 3D - 2011

University of Illinois at Chicago


CAVE 2 – Oct 2012

University of Illinois at Chicago


Positive Parallax

The left and right eye images projected on the screen


Negative Parallax

• If Objects are too close in front of the projection plane, negative parallax will increase.

• If negative parallax is wider than eye separation, then result is pain.


Zero Parallax(when the object is actually on the screen)


Correct Stereo Computer Graphics

Asymmetric View Frustum


Stereo Approximation

LeftEye

RightEye

Projection Planes are not the same

• There is potential for eye discomfort for objects that are too close because an object may appear to be cut off at the edges for one of the eyes.

• Enlarging eye separation makes the problem worse.


Making the graphics looktrue to size regardless of screen size

• Set camera properties to be the same as real world properties:– Set user’s distance to screen (ie focal length d)– Measure the screen’s height (h)– Compute the field of view (f = 2*atan(h/2d))– Use real world eye separation distance (2.5 inches)

LeftEye

RightEye

dh

f

E.g. A 1 foot object should appear to be the right size regardless of screen size.


Small screen

Big screen


In Movies and Video Games True Size is Generally Never Used

Yoda is not 30 feet tall…


Note the separation of 2 points on an image here

Eyes

Lets say you created a stereo image for a small desktop display…

In 3D Things Can Get Painful


Eyes

… then you decide to run your application on a BIG display!

Same can happen if you sit too close in a 3D movie


General Recommendation

• General guideline is make eye separation no more than 1/20 of d

• This gives us an angle of about 1.5 degreesi.e. atan(1/20/2 / d)

1/20 of d

d


General Recommendation

• Same therefore goes for any object in the scene.• It should not project an image on the screen of size DX that is

larger than your eye separation.• t = 2 atan(DX / 2d)

t


Say an object is too close…Now t >> 1.5And DX >> Eye Separation

DX Eye

Separation

• But remember for large screens DX will be big.• So you really have to be conservative about

how close you can put your object.• Often you will hear recommendations of setting

eye separation to 1/30 or 1/100


Tips

• Use 2D depth cues.• When using 3D it’s safest to put objects behind the screen –

but not too far or the depth effect is lost.• Bring objects in front of projection screen sparingly and be

careful how close they come. • Be careful with wild camera swings.• Your game may slow down as much as by half to render the

second eye.• Keep eye separation at no more than 1/20 the distance to

projection screen or object.• Test your game on the target display platform don’t assume it

will just look fine..


OLD SLIDES


Stereo in Unity3D


Ways of Seeing Stereo

Passive Stereo GeoWall

Active Stereo LCD Shutter glasses

Passive Stereo LCD

Autostereo LCD (Varrier)


Stereo in Electro

• electro.exe -f config/geowall-side-by-side-config.lua …..• set_camera_stereo(camera, mode, Lx, Ly, Lz, Rx, Ry, Rz)• Set stereo options on the given camera. The mode

argument gives the stereo method, as described below. The (Lx, Ly, Lz) and (Rx, Ry, Rz) arguments give the offsets from the camera to the user's left and right eyes.

• Available stereo modes :– stereo_mode_none– stereo_mode_tile - GeoWall side-by-side stereo– stereo_mode_quad - LCD shutter glasses stereo– stereo_mode_red_blue - red/blue stereo– stereo_mode_varrier_11, * stereo_mode_varrier_33 - autostereo


GeoWall Stereo Config for Electro• W = 5.1666 -- The Geowall in the AG Room is 5'2"• H = 4.1666 -- by 4'2".• D = 10.0000 -- The ideal viewing position is 10' from the center.• O = 0.15 -- The interocular distance• S = 8 -- orthagonal camera pixel seperation (hack)

• w = 2048• h = 768• ------------------------------------------------------------------------------• tile = { }

• host = E.add_host("default", 0, 0, w, h)• tile[1] = E.add_tile(host, 0, 0, w / 2, h)• tile[2] = E.add_tile(host, w / 2, 0, w / 2, h)

• E.set_tile_position(tile[1], -W / 2, -H / 2, -D, W, 0.0, 0.0, 0.0, H, 0.0)• E.set_tile_position(tile[2], -W / 2, -H / 2, -D, W, 0.0, 0.0, 0.0, H, 0.0)

• E.set_tile_viewport(tile[1], S, 0, w / 2, h)• E.set_tile_viewport(tile[2], -S, 0, w / 2, h)

• E.set_tile_view_offset(tile[1], -O / 2, 0, 0)• E.set_tile_view_offset(tile[2], O / 2, 0, 0)

• E.set_host_flags(host, E.host_flag_full, true)


Stereo API in BlitzGeoWallStereoLib.bb

• 3 Main Calls:• 1. Create 2 cameras and return the main camera

(left camera)– mainCamera = SL_CreateStereoCameras()

• 2. Set up the stereo camera viewports– SL_SetUpCameras()– SL_SetEyeSeparation(separationValue#)

• 3. Update stereo cameras just before each Render call (basically to update the right camera)– SL_Update()


Other Useful Calls

• Call these only if for some reason you want to manually create each camera– Camera=SL_CreateLeftCamera()– Camera=SL_CreateRightCamera()

• Call this if you have your own cameras created and want to use them as the stereo cameras– SL_SetLeftCamera(camera)– SL_SetRightCamera(camera)

• Just accessor functions– Camera=SL_GetLeftCamera()– Camera=SL_GetRightCamera()

• Switch to monoscopic viewing– SL_SwitchToMono()

• Switch to Stereo viewing– SL_SwitchToStereo()

• Use this to set near correct scaled stereo. Ie. A 1 foot object will appear 1 foot in size on the screen given the height and distance to the screen.– SL_SetUpCorrectScaleStereo(screenWidth#, screenHeight#,

distanceToScreen#)


Final Comments

• Use the

BLITZ_GEOWALL_GAME_ENGINE_TEMPLATE to begin writing your own Blitz3D GeoWall Stereo Program

• Template includes both stereo calls and proper game loop with Tweening.

electronic visualization laboratory, university of illinois at chicago stereoscopic computer...

Documents

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