OpenCASCADE v6.1.0 Transparency

I'm loading a model file and have a slider bar to change the transparency of the shape in the view. Sliding the bar down to 0% transparency and you can see the transparency jump from partial transparency to solid.

It seems to look different from v5.2, is this a new feature or a bug in v6.1.0.


Forum supervisor's picture

Hello Jonathan,

As distinct from OCCT 5.2, OCCT 6.1 features improved presentation of transparent objects based on the recommended rules of presentation of transparent objects in OpenGl. Schematically the recommendation can be illustrated like following :


Apparently the changes in the algorithms lead to changes in visual presentation of objects. However the "jump" effect you noticed should exist in all versions of OCCT. It is reached when setting the minimal value of transparency (0.05). In OCCT, if the transparency value is less than 0.05, the object is presented as solid.

Best regards,
Forum Supervisor

Jonathan Hill's picture


Thanks for explaining how it works :)
I'm happy that my code is working how it should Ta.


Mark Whitis's picture

Looks pretty broken in the test harness.

cd /opt/OpenCASCADE6.2.0/ros/src/DrawResources
pload ALL
source $env(CSF_XCAFDefaults)/dftree.tcl
source VisualizationDemo.tcl

# Not at all transparent
vsettranparency result 0.9
#broken: Object is not displayed as transparent
vsetdispmode 2 # completely broken, shows objects that aren't even in scene
vsetdispmode 3 # completely broken, blank output

objects are inappropriately refreshed under some circumstances. Drag another window so it partially covers two of the views, then drag it some more. It appears this initiates a large number of redraws, failing to abort a previous redraw when the next is triggered. This can cause the window to spaz for seconds or minutes.

Killing any of the windows causes the test harness to abort.

debian unstable, nvidia graphics accellerator