bugpyFormex - Bugs: bug #41549, alpha and bkalpha


bug #41549: alpha and bkalpha

Submitter:  gianluca de santis <gianlucadesi>
Submitted:  Tue 11 Feb 2014 02:59:37 PM UTC
Category:  Rendering Severity:  3 - Normal
Item Group:  Feature request Status:  Ready For Test
Privacy:  Public Assigned to:  bverheg
Open/Closed:  Open
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Thu 13 Feb 2014 04:21:02 PM UTC, comment #5: 

The transparency (alpha and bkalpha) works file with pyFormex but when exporting to webGL and visualizing on a web browser the alpha and bkalpha are not ok. This is due to the faces.opacity in the .js file which over-rule the back.opacity and front.opacity.
By just commenting this faces.opacity, front.opacity (alpha) and back.opacity (bkalpha) work fine!

object_59_back.opacity 0.7
object_59_front.opacity 0.2
object_59_faces.opacity = 1.0;

Could this be fixed when exporting webGL from pyFormex GUI?

gianluca de santis <gianlucadesi>
Group Member
Tue 11 Feb 2014 09:34:57 PM UTC, comment #4: 

The problems with lines and wireframe mode are fixed in 25a6bbf.

Benedict Verhegghe <bverheg>
Group administrator
Tue 11 Feb 2014 08:12:03 PM UTC, comment #3: 

It works nice with surfaces but lines (and edges) cannot be correctly visualized. Lines are also wrong when switching a surface mesh to wireframe mode (even without transparency).
Does it happen also to you guys?

gianluca de santis <gianlucadesi>
Group Member
Tue 11 Feb 2014 07:35:56 PM UTC, comment #2: 

In a62b0a0 we have implemented different alpha and bkalpha values.
It has currently only been tested on the opengl/example2 script. Notice how the front of the green plate is (almost) opaque, while the back side is transparent.

Further testing is required though, also to see if no problems were introduced for other cases. Please report.

Benedict Verhegghe <bverheg>
Group administrator
Tue 11 Feb 2014 06:57:35 PM UTC, comment #1: 

This was until now impossible to do, because our renderer draws both front and back sides of the triangles. There were two reasons for this: enable different back and front side color, and remove some artefacts that we were not able to eliminate in an other way. Because of this double drawing, it makes no sense to use different alphas, as both values are drawn in each case.

However, in commit 782d5c8 we have changed the shaders so that triangles with normal oriented away from the camera are discarded,
and thus far we have not seen any artefacts reappearing because of the change.
This will make it possible to introduce different front and back opacity.

Benedict Verhegghe <bverheg>
Group administrator
Tue 11 Feb 2014 02:59:37 PM UTC, original submission:  

With gl2 the bkalpha seems not considered (or alpha and bkalpha are always the same).I would need to draw objects which are transparent from the front and non-transparent from the back. Could this be added?

gianluca de santis <gianlucadesi>
Group Member


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    Follow 5 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2014-02-11 bverheg StatusIn Progress Ready For Test
    2014-02-11 bverheg CategoryNone Rendering
        Item GroupNone Feature request
        StatusNone In Progress
        Assigned toNone bverheg

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