Cycling 74 » Topic: simple GL render order question http://cycling74.com/forums/topic/simple-gl-render-order-question/feed Tue, 18 Jun 2013 21:02:56 +0000 http://bbpress.org/?v=2.2.4 http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-40712 <![CDATA[simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-40712 Thu, 06 Nov 2008 19:40:45 +0000 Zachary Seldess Hi everyone,

Simple render ordering confusion here. Can someone help clarify? This is so simple, in fact, that I must be having some sort of brain fart to not get it. I control render ordering all the time without problem, but I just don’t understand the logic behind the following behavior. There seems to be a contradiction between what is written and what actually happens (or, more likely, I’m missing something).

——————-
From Max 5 Jitter Tutorial 31:

“Each time a jit.gl.render object receives a bang message, it draws all of the GL group objects that have been added to its context. It draws the objects in the order in which they were added to the context. In this case, the yellow circle was added to the draw context named “B” after the blue circle, so it appears on top. To change this order, we can send the message drawto B to the jit.gl.gridshape object drawing the blue circle again. This will remove it from its present place in the list of objects for the context named B, and add it again at the end of the list.”
——————–

But in fact, I get the opposite behavior when running the tutorial patch (Max5 as well as the corresponding Max4.6 patch). It seems that with @depthbuffer 0 @automatic 1, sending the drawto message to an object causes it not to render last, but instead it seems to pop it to the front of the list.

Here’s an example patch, but you could just as easily look at the Tut patches.

– Pasted Max Patch, click to expand. –

Zachary

]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144322 <![CDATA[Re: simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144322 Thu, 06 Nov 2008 22:23:44 +0000 yair reshef hi zack, tutorial 31 has always been a cause of confusion, here is thread in
which wes offers an fixplenation

“If you set @depth_enable 0, there are no order issues. Everything is
drawing at z=0.”

http://www.cycling74.com/forums/index.php?t=msg&goto=142292

On Thu, Nov 6, 2008 at 9:40 PM, Zachary Seldess wrote:

>
> Hi everyone,
>
> Simple render ordering confusion here. Can someone help clarify? This is so
> simple, in fact, that I must be having some sort of brain fart to not get
> it. I control render ordering all the time without problem, but I just don’t
> understand the logic behind the following behavior. There seems to be a
> contradiction between what is written and what actually happens (or, more
> likely, I’m missing something).
>
> ——————-
> >From Max 5 Jitter Tutorial 31:
>
> “Each time a jit.gl.render object receives a bang message, it draws all of
> the GL group objects that have been added to its context. It draws the
> objects in the order in which they were added to the context. In this case,
> the yellow circle was added to the draw context named “B” after the blue
> circle, so it appears on top. To change this order, we can send the message
> drawto B to the jit.gl.gridshape object drawing the blue circle again. This
> will remove it from its present place in the list of objects for the context
> named B, and add it again at the end of the list.”
> ——————–
>
> But in fact, I get the opposite behavior when running the tutorial patch
> (Max5 as well as the corresponding Max4.6 patch). It seems that with
> @depthbuffer 0 @automatic 1, sending the drawto message to an object causes
> it not to render last, but instead it seems to pop it to the front of the
> list.
>
> Here’s an example patch, but you could just as easily look at the Tut
> patches.
>
>

– Pasted Max Patch, click to expand. –

>
> Zachary
> –
> http://www.zacharyseldess.com
>
>

]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144323 <![CDATA[Re: simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144323 Thu, 06 Nov 2008 22:58:24 +0000 Joshua Kit Clayton On Nov 6, 2008, at 11:40 AM, Zachary Seldess wrote:

> Simple render ordering confusion here. Can someone help clarify?
> This is so simple, in fact, that I must be having some sort of brain
> fart to not get it. I control render ordering all the time without
> problem, but I just don’t understand the logic behind the following
> behavior. There seems to be a contradiction between what is written
> and what actually happens (or, more likely, I’m missing something).

Hi Zachary,

Sorry for any confusion in this tutorial. In general, the order added
to the context should not be relied upon and may have changed as the
implementation changed throughout the years. If you need to specify
ordering, please use the @layer implementation which is guaranteed to
be effective for this sort of thing. If you are on PC, certain OpenGL
drivers will always allocate a depth buffer even if requesting not to
allocate on, so you must explicitly disable depth buffering for the
objects being rendered for “painter’s algorithm” rendering.

-Joshua

]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144324 <![CDATA[Re: simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144324 Fri, 07 Nov 2008 00:29:52 +0000 Zachary Seldess Thanks Joshua and Yair.

Joshua, good to know my confusion was somewhat founded. I typically use the layer method or just bang order @automatic 0, but I wanted to clear this drawto confusion up, just so I had an explanation for others. Anyways, at least on my machine, drawto behaves consistently (moving the object to the front of the render list) – I like consistency, even if it’s contrary to what I would imagine!

Yair, thanks for the link. With my drawto example patch, on Mac, altering the objects’ depth_enable attribute doesn’t change the behavior. No problem as, again, it’s consistent, and I don’t control render order this way anyways.

Thanks guys.

Zachary

]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144325 <![CDATA[Re: simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144325 Fri, 07 Nov 2008 02:32:01 +0000 Zachary Seldess Joshua, Yair, and others,

Here’s another related question:

Let’s say I have one object @transform_reset 0 (normal) and another @transform_reset 1. If the jitter window is @depthbuffer 0 then the objects’ layer attributes will allow me to fully control the render order – effectively placing the @transform_reset 1 permanently in the background, or permanently in the foreground (HUD-style). But if the window is @depthbuffer 1, layers no longer seem to control render order – the object @transform_reset 1 ALWAYS renders last (i.e. “in front”), regardless of which layer it is. Layers DO still control blending behavior though.

So the question is… can you use @depthbuffer 1 AND have the object @transform_reset 1 render “behind” the other object. If not, can you explain why? Thanks.

best,
Zachary

Here’s the patch:

– Pasted Max Patch, click to expand. –

]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144326 <![CDATA[Re: simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144326 Fri, 07 Nov 2008 02:44:21 +0000 Joshua Kit Clayton On Nov 6, 2008, at 6:32 PM, Zachary Seldess wrote:

> Let’s say I have one object @transform_reset 0 (normal) and another
> @transform_reset 1. If the jitter window is @depthbuffer 0 then the
> objects’ layer attributes will allow me to fully control the render
> order – effectively placing the @transform_reset 1 permanently in
> the background, or permanently in the foreground (HUD-style). But if
> the window is @depthbuffer 1, layers no longer seem to control
> render order – the object @transform_reset 1 ALWAYS renders last
> (i.e. “in front”), regardless of which layer it is. Layers DO still
> control blending behavior though.

This means that depth buffering is doing the right thing. Depth
buffering works independent of render order. You get over this issue
by either moving the objects you wish to be “on top” closer to (or “on
bottom” further from) the camera (orthographic projection often useful
for such a purpose), or by resetting the depth buffer with the
@depth_clear attribute:

depth_clear (int): Depth buffer clear flag (default = 0) When the flag
is set, the depth buffer is cleared before rendering the object.

> So the question is… can you use @depthbuffer 1 AND have the object
> @transform_reset 1 render “behind” the other object. If not, can
> you explain why? Thanks.

@depth_clear 1 for the object in the next layer above.

-Joshua

]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144327 <![CDATA[Re: simple GL render order question]]> http://cycling74.com/forums/topic/simple-gl-render-order-question/#post-144327 Fri, 07 Nov 2008 03:33:56 +0000 Zachary Seldess Ah, Excellent. I’d never used @depth_clear before, works great.

“This means that depth buffering is doing the right thing. Depth buffering works independent of render order. You get over this issue by either moving the objects you wish to be “on top” closer to (or “on bottom” further from) the camera…”

But just to be clear, with @depthbuffer 1, moving the objects in reference to the camera doesn’t get over the issue on my machine (object with @transform_reset 1 renders “on top”, regardless). @depth_clear 1 works beautifully though, thanks!

best,
Zachary

]]>