FreeCADView Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0000196 | FreeCAD | Bug | public | 2010-11-06 22:55 | 2010-11-29 17:39 |
| Reporter | unauthenticated | Assigned To | |||
| Priority | normal | Severity | minor | Reproducibility | always |
| Status | closed | Resolution | fixed | ||
| Product Version | 0.11 | ||||
| Summary | 0000196: Enabling transparency on non-primitive object changes the appearance of other objects | ||||
| Description | If you take a revolved object, and put a cylinder half into it, when giving transparency to the object, the cylinder is rendered with the transparency too, if the camera sees the cube behind the cylinder. Discovered in version 3696. | ||||
| Tags | No tags attached. | ||||
| FreeCAD Information | |||||
|
|
Just a fix on my report, the rendering problem also occurs on objects placed above the transparent object, not only objects placed mid-through it. |
|
2010-11-07 19:45
|
|
|
|
For me it transparency looks OK (see attached screenshot). Can you post a screenshot? |
|
|
In fact, the error appears on small scale. If objects are too distant, the problem does not show up. As well, when the object exceeds a lot the transparent object, it can't easily be seen. But with some precision machinery, you have to have this bug. Thanks for having tried already! |
|
2010-11-07 22:42
|
|
|
2010-11-07 22:43
|
|
|
|
For me it looks like an opengl clipping artifact (it happens in almost all opengl applications I know). It would be interesting if you could explain precisely what you did to obtain this artifact? |
|
|
(I'm the reporter) Maybe this is an OpenGL issue, I don't really know. What I feel, is that there is a computation problem somewhere because it only happens on the rendering of faces of objects that are close from the transparent shape. If I take the cylinder and put the revolved object in the middle, the problem does not clearly appear, like you did in your screenshot. It is an issue only on faces of objects that are close enough from the transparent object, and when the transparent object is behind them I think. It's quite hard to explain, but when you move the camera when objects are close from each other, or do not exceed each other much when they intersect, the transparency of non-transparent objects seems modified, and that, not homogeneously. I mean the object that is close from the transparent object is displayed sometimes with an oval transparency artifact which moves depending on the direction of the camera. Maybe it happens to me a lot because I work with objects of small sizes too. |
|
|
What do you mean by very small size? Can you give me an example so I can try something similar? |
|
|
If I remember correctly, the improperly-rendered object are closer or smaller than around 2 (FreeCAD units) from the transparent object. If you really have problems reproducing, I'll try to make a simple sequence that fails for me. |
|
|
I found a very simple example to illustrate the bug: - create a shpere (radius=2) - enable transparency on the sphere and color it - create a cylinder -> you will see the sphere through the cylinder. |
|
2010-11-21 18:28
|
|
|
2010-11-21 18:29
|
|
|
|
I couldn't reproduce your bug exactly, but I found other artifacts that might be related. I just uploaded 2 new screenshots, doing the sphere and the cylinder as in your example above. Screenshot opengl1.jpg shows what appears immediately after creating both objects and setting transparency: Everything is normal, from whatever angle and whatever distance you see the objects. Screenshot opengl2.jpg shows what happens when you hover the mouse on the objects, preselecting them, then hovering to another view... The preselection mechanism redraws the preselected object on top of the other objects, and sometimes this happens in wrong order Would that be related to your bug? Could you try the following? - See if there is any difference if object 1 is selected, or object 2, or both, or neither - Try disabling selection & preselection highlight in the preferences and see if there is any difference? |
|
|
Sorry, I just noticed I has missed something in my example, I edited the previous note while you were posting. The sphere should have had the same radius than the cylinder, in which case the top of the sphere shouldn't be seen at all, but it is (at least on my computer). To reply to your last question, the bug I report here it not related to the preselection, but I agree that selection and preselection are quite working randomly too. |
|
|
Hi guys, its actually not a bug (yea I know, all developer say that) but! .... OpenGL can not really deal very good with transparency. The shapes get normally rendered in arbitrary order. Unfortunately to get real transparency you have to render the farer pieces first and overlay the nearer (transparent) pieces. Coin does that by sorting bevor rendering. It has some kind tricks to do that in good performance. But that has its limitation especially in self intersecting situations. Its not a bug, you just can not do it better without huge performance loss.... Raytracing give the only perfect thing in this cases.... |
|
|
Its a problem but whont fix |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2010-11-06 22:55 | unauthenticated | New Issue | |
| 2010-11-07 13:06 | unauthenticated | Note Added: 0000401 | |
| 2010-11-07 19:45 | yorik | File Added: transparency.jpg | |
| 2010-11-07 19:46 | yorik | Note Added: 0000403 | |
| 2010-11-07 22:10 | unauthenticated | Note Added: 0000404 | |
| 2010-11-07 22:42 | unauthenticated | File Added: transp_off.png | |
| 2010-11-07 22:43 | unauthenticated | File Added: transp_on.png | |
| 2010-11-07 22:47 | unauthenticated | Note Edited: 0000404 | |
| 2010-11-13 18:55 | yorik | Note Added: 0000412 | |
| 2010-11-13 19:01 | yorik | Status | new => feedback |
| 2010-11-13 21:08 | myier | Note Added: 0000416 | |
| 2010-11-13 21:31 | yorik | Note Added: 0000417 | |
| 2010-11-13 22:07 | myier | Note Added: 0000420 | |
| 2010-11-21 18:08 | myier | Note Added: 0000431 | |
| 2010-11-21 18:28 | yorik | File Added: opengl1.jpg | |
| 2010-11-21 18:29 | yorik | File Added: opengl2.jpg | |
| 2010-11-21 18:35 | yorik | Note Added: 0000432 | |
| 2010-11-21 18:35 | myier | Note Edited: 0000431 | |
| 2010-11-21 18:39 | myier | Note Added: 0000433 | |
| 2010-11-29 17:38 |
|
Note Added: 0000443 | |
| 2010-11-29 17:39 |
|
Note Added: 0000444 | |
| 2010-11-29 17:39 |
|
Status | feedback => confirmed |
| 2010-11-29 17:39 |
|
Status | confirmed => closed |
| 2010-11-29 17:39 |
|
Resolution | open => fixed |
