puts "This test case handles a specific task:"
puts "to draw 2d objects in same scene with 3d objects while 2d objects need to be drawn in specific order on 3d plane and overlap correctly with 3d objects."

pload MODELING VISUALIZATION
vinit View1
# Thin boxes represent overlapping 2d objects in same plane
# Normally such configuration would cause z-fighting noise (flickering)
box b1 -0.75 -0.75 0 1 1 0.01
box b2 -0.50 -0.50 0 1 1 0.01
box b3 -0.25 -0.25 0 1 1 0.01
vdisplay b1 b2 b3 -dispMode 1
vaspects b1 -material brass
vaspects b2 -material silver
vaspects b3 -material copper
# Set object polygon mode Aspect_POM_None to inherit Z-Layer settings,
# as default object polygon offset is "Aspect_POM_Fill 1 1" (overrides Z-layer settings)
vpolygonoffset b1 8 0 0
vpolygonoffset b2 8 0 0
vpolygonoffset b3 8 0 0

psphere s 0.3
vdisplay s -dispMode 1
vaspects s -material brass
vpolygonoffset s 8 0 0

# Create new z-layer for 3d objects
catch { vzlayer -delete 1 }
set aLayerId [vzlayer add]
vdisplay s -layer $aLayerId

# Disable OpenGL depth test for layer 0 (to eliminate flickering)
# But depth write is still enabled
vzlayer DEFAULT   -disable depthTest

# Disable depth buffer clearing for layer 1 (we want correct overlapping with 3d objects)
vzlayer $aLayerId -disable depthClear

# List currently enabled settings of each layer
vzlayer DEFAULT   -settings
vzlayer $aLayerId -settings

# "3d" box with one of its faces on same plane with "2d" objects
# Normally this also would cause flickering because new box is
# supposed to be in layer 1 as "3d" structure, thus depth test between
# new box and "2d" objects will be enabled.
box b 0 0 0.01 0.5 0.5 -0.5
vdisplay b -dispMode 1 -layer $aLayerId
vaspects b -material brass
vpolygonoffset b 8 0 0

# To handle this situation, depth offset setting was introduced.
# It implemented with glPolygonOffset calls per layer.
# Set polygon offset 2 (greater than default value 1 to see the difference).
vzlayer 1 -enable depthoffset 2 1

vfit
vdump $imagedir/${casename}.png