Visualization / Layer origin

Script demonstrates usage of Graphic3d_ZLayerSettings::Origin() property to display presentations at large distance from world origin.

Distance (10^x)

First label “KO Premultiplied” is displayed with premultiplied large transformation. TopLoc_Location with large distance is set to TopoDS_Shape and displayed as AIS_Shape having identity local transformation. This leads to severe visual artifacts due to insufficient single floating point precision of vertex data uploaded onto GPU and calculations in GLSL program.
Second label “KO Located” is displayed with transformation assigned to presentation. TopoDS_Shape has identity or small location and displayed as AIS_Shape. AIS_Shape::LocalTransformation() is set to large displacement. This allows to avoid vertex corruption as could be seen in first sample, but presentation jitters during camera rotation due to insufficient single floating point precision of transformation matrix uploaded onto GPU.
Third label “OK ZLayer origin” displays located presentation close to Z-Layer origin. As in case of second label, TopoDS_Shape has identity or small location and displayed as AIS_Shape; AIS_Shape::LocalTransformation() is set to large displacement. In addition, Graphic3d_ZLayerSettings::Origin() of Z-Layer used for displaying the object is moved close to presentation. This activates a special workflow temporarily moving camera to Z-Layer origin, so that single floating point precision becomes enough to display presentation without artifacts.

This approach could be used to display objects within large distances, or to preserve desired precision while aggressively zooming-in.

Tcl C++

pload MODELING VISUALIZATION

set aDist [expr pow(10, 7)]
set aHeight 20
set aThick  10
set aPlane {0 -1 0 1 0 0}

vinit View1
vfront
vviewparams -proj 0.1 -1.0 0.1

# location is premultiplied to vertices position
text2brep t1 "KO Premultiplied" -plane {*}$aPlane -height $aHeight
prism t1 t1 0 $aThick 0
ttranslate t1 $aDist 0 50
vdisplay -dispMode 1 t1
vaspects t1 -color RED

# location is set to presentation
text2brep t2 "KO Located" -plane {*}$aPlane -height $aHeight
prism t2 t2 0 $aThick 0
vdisplay -dispMode 1 t2
vlocation t2 -location $aDist 0 0
vaspects t2 -color YELLOW

# location is set to presentation + to Z-Layer origin
text2brep t3 "OK ZLayer origin" -plane {*}$aPlane -height $aHeight
ttranslate t3 0 0 -50
prism t3 t3 0 $aThick 0

set aLayer [vzlayer -insertBefore DEFAULT -origin $aDist 0 0]
vselprops dynHighlight -layer -1
vdisplay -dispMode 1 t3 -zlayer $aLayer
vlocation t3 -location $aDist 0 0
vaspects t3 -color GREEN

vdrawtext t4 "$aDist" -pos [expr $aDist + 100] 0 -70 -height 30 -plane {*}$aPlane -halign center -color GREEN

box b -5 -100 -100 200 200 200
vdisplay -dispMode 0 b -zlayer $aLayer -noselect
vlocation b -location $aDist 0 0

vfit