How to clear up things drawn by the displayPipeline?

Replies to This Discussion

Permalink Reply by David Rutten on January 21, 2012 at 1:01am

Hi Jerome,

if you want to draw your own geometry, I recommend PostDrawObjects, not DrawForeGround.

What exactly do you mean by "clear up"? 

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Jerome on January 21, 2012 at 1:31am

Hi, David.

The geometry I draw using DrawForeGround always stays in the viewport. Is it possible to make these geometries disappear from the viewport?

By the way, what is the difference and advantages of PostDrawObjects and is there an example to use it?

Thanks!

-Jerome

Permalink Reply by michael sprinzl on January 21, 2012 at 1:40am

I think the best is to handle this is by ref. When you can dispose what you have done. Else you drawings will be in Rhino till closing of application. If this is the problem...

Rhino.Display.CustomDisplay my_disp = new Rhino.Display.CustomDisplay (true);

my_function_i_will_do_something(my_disp);

my_dis.dispose();

my_function_i_will_do_something(ref Rhino.Display.CustomDisplay my_pass_throught)

{

do what ever .... paint play etc...

}

Permalink Reply by David Rutten on January 21, 2012 at 1:58am

CustomDisplay does indeed have that problem, but when you draw it yourself using methods like PostDrawObjects() then you have to keep drawing your geometry on every viewport refresh.

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Jerome on January 21, 2012 at 7:35pm

Thanks, Michael

I've never used CustomDisplay before and I will have a try on it. It looks like there are less methods than those of DisplayPipeline. 

Thanks!

-Jerome

Permalink Reply by David Rutten on January 21, 2012 at 2:01am

DrawForeground is specifically designed to draw stuff on top of the viewport. There's no Z-testing anymore either.

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Jerome on January 21, 2012 at 7:30pm

Thanks, David.

I tried PostDrawObjects() on every refresh of my animation and it works pretty good! I read the article of the display conduit on the rhino page and still haven't got a good idea about the Z-tesing. Is it the same thing as the depth testing? Could you explain it a little?

If I use PostDrawObjects(), is it still necessary to use CalculateBoundingBox to ensure that nothing will be clipped in the viewport?

Thanks a lot!

-Jerome 

Permalink Reply by David Rutten on January 22, 2012 at 1:50am

Z-testing and depth-testing is the same thing. OpenGL tends to draw a z-buffer image along with the regular image. It's easiest to think of a z-buffer as a greyscale image where black represents the furthest possible distance from the camera and white the smallest possible distance. Every pixel of every object that is drawn is compared against the z-buffer and only allowed to be really drawn if it's closer to the camera than the z-buffer pixel was. This is how OpenGL figures out which parts of objects are occluded by other objects.

It is possible to disable the depth-testing, which means that everything you draw, no matter how far away, will always be visible. It is also possible to disable depth-writing, which allows you to draw pixels at a depth that remain unknown to the z-buffer.

When I say "furthest possible distance" and "smallest possible distance" I do not mean infinity and zero. Indeed, there are only so many unique shades of grey between black and white so the tighter this range from black to white the better the depth-clipping will work. This is where CalculateBoundingBox comes in. Before the black-white range is assigned, CalculateBoundingBox is used to determine the size of the entire scene to be drawn. If you want to draw geometry outside of the scene boundingbox then you run into problems with the z-buffer, because there is no colour (darker than black and brighter than white are not possible) that can possibly represent your pixels. So, yes, you do need to handle CalculateBoundingBox when you intend to draw depth-clipped geometry.

--

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Jerome on January 22, 2012 at 2:44am

Thanks, David

Your introduction to the z-buffer is quite thorough and clear. It almost cover everything I previously got confused when I need my things properly drawn in the viewport.

Thank you so much!

-Jerome

Permalink Reply by Giulio Piacentino on January 21, 2012 at 8:39am

Hi Jerome,

if you on the other hand are meaning "how to deregister the paint delegate"?

That is then:

Rhino.Display.DisplayPipeline.DrawForeground -= new EventHandler<Rhino.Display.DrawEventArgs>(OnDrawForeground);

Delegates are considered equal if they point to the same instance (if any) and same method.

- Giulio
______________
giulio@mcneel.com

Permalink Reply by Jerome on January 21, 2012 at 7:44pm

Thanks, Giulio

I added that deregister line in my code originally and perhaps not in a good place. Everytime I start my animation use a boolean toggle, it will clear those things drawn previously and start a new animation, which is the case I wanted. However, after I clicked into the c# component and clicked OK to exit, then I clicked the boolean toggle to start the animation, the old objects will be still there. Maybe there's something wrong with the logic of my code and I will look into it. 

Thank you for your help!

-Jerome

Permalink Reply by Giulio Piacentino on January 23, 2012 at 2:16am

Yes, you might want to keep track of which one was the last callback that you registered, and before adding a new one, always de-register at least the previous one.

Does that make sense?

- Giulio
_______________
giulio@mcneel.com

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