Alpha Channel display bug

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Alpha Channel display bug

Postby ajiblock » Sun Jan 21, 2018 5:16 pm

ajiblock Sun Jan 21, 2018 5:16 pm
Hi,
I'm experiencing very weird performance with alpha channels in live viewer. Downloaded the Houdini Octane Demo to test the look of a project. I have a sphere made of many particles, in live viewer by default I see the Octane Environment in the background, I don't want this to show so I check "alpha channel" to remove the environment, but that then changes the density of the particle sphere. When I've used Octane in C4D turning on Alpha Channel has never affected the actual image, even with particle renders. You can see in the two attached screenshots, it looks correct / how I would expect in the image with the environment showing, but I obviously need to be able to see it without the environment in the background without the density changing to be able to work properly.

Not sure if this is only an IPR bug or if it's happening when rendering, I'm still on the demo as I wanted to make sure this would work before getting the full version. If this is something demo specific tho happy to get the full version to alleviate the issue. I'm on Houdini 15.5.717 OSX with the latest version of Octane Demo.
Thanks
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Screen Shot 2018-01-21 at 12.06.13 PM.png
Screen Shot 2018-01-21 at 12.05.59 PM.png
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Re: Alpha Channel display bug

Postby juanjgon » Mon Jan 22, 2018 10:15 am

juanjgon Mon Jan 22, 2018 10:15 am
Hi,

I'm not sure what could be the problem. Can you please send me the scene to test it here?

Thanks,
-Juanjo
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Re: Alpha Channel display bug

Postby ajiblock » Mon Jan 22, 2018 6:37 pm

ajiblock Mon Jan 22, 2018 6:37 pm
Hi,
just sent you a file, thanks so much!
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Re: Alpha Channel display bug

Postby juanjgon » Mon Jan 22, 2018 11:56 pm

juanjgon Mon Jan 22, 2018 11:56 pm
Hi,

I'm testing your scene, and well, I think that this is the expected behavior. Your object has zones with transparency that are affecting the alpha channel, as you can see in the attached image. With the alpha enabled, the object is mixed with the background, that is blue/white, but without the alpha channel enabled, all these transparent zones are black.

Hope this helps,
-Juanjo
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2018_01_23-00_52_05.jpg
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Re: Alpha Channel display bug

Postby ajiblock » Tue Jan 23, 2018 3:24 pm

ajiblock Tue Jan 23, 2018 3:24 pm
Hi Juan,
Thanks for testing this out, much appreciated. Your response makes sense, the only reason I posted as a bug report was after caching the particles and trying them in C4D Octane the live viewer/alpha channel behavior was different, so assumed it might be a bug. Just starting with Houdini/Octane.

I did have one point of clarification – in my original screenshots, when alpha is enabled, the background in the live viewer is black. When alpha is disabled, the background is white/blue (also wondering if there is a way to remove that background independent of alpha?).

This line from your post "With the alpha enabled, the object is mixed with the background, that is blue/white, " is where you lose me, as stated, in my screenshot when alpha is enabled, the background is showing in live viewer as black, so my expectation is that the object is mixing with the black background due to alpha, not the blue/white. Apologies if I'm just being dense here.
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Re: Alpha Channel display bug

Postby juanjgon » Thu Jan 25, 2018 10:24 pm

juanjgon Thu Jan 25, 2018 10:24 pm
Yes, sorry. You are right. When the alpha is enabled, the environment background is disabled, rendering the whole scene over a black background. When the alpha is disabled, the scene is rendered with the environment background, so you can see the background through the object transparent surfaces. There is also an option to keep the environment while the alpha is enabled.

Thanks,
-Juanjo
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Re: Alpha Channel / particle scale / Cd tex issues

Postby ajiblock » Sat Jan 27, 2018 6:05 am

ajiblock Sat Jan 27, 2018 6:05 am
juanjgon wrote:Yes, sorry. You are right. When the alpha is enabled, the environment background is disabled, rendering the whole scene over a black background. When the alpha is disabled, the scene is rendered with the environment background, so you can see the background through the object transparent surfaces. There is also an option to keep the environment while the alpha is enabled.

Thanks,
-Juanjo


Hey Juan,
Thanks for clarifying. I'm having a few other issues that are seriously preventing me from working. I updated the topic to include the other issues but can open a new topic if thats preferred.

I'm trying to configure particle scale and am noticing no changes. I've changed the multipliers by large margins but the image looks identical. I am setting particle with my wrangle node at the geometry level but even when I delete that setting and try to set particle scale exclusively with the Octane OBJ parameters nothing is changing. Additionally, nothing is refreshing in Mplay when I change a Octane OBJ param. I'm having to close Mplay and reopen to try and see any change – is there no way to refresh ?

Also, whenever I open IPR on the scene for the first time, or when I go to render, the output is grey and uncolored. In IPR I can get it to work by checking off and on the 4k RGB texture reference in the shader, but currently can't get anything but grey in my render.
Attachments
Screen Shot 2018-01-27 at 12.31.11 AM.png
Screen Shot 2018-01-27 at 12.31.43 AM.png
Screen Shot 2018-01-27 at 12.32.51 AM.png
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Re: Alpha Channel display bug

Postby juanjgon » Mon Jan 29, 2018 10:21 am

juanjgon Mon Jan 29, 2018 10:21 am
Hi,

It is true that some events, like updating parameters at OBJ level are not updated in the IPR in real time without reloading the scene, but you don't need to close MPLay and open it again to reload the scene. Have you seen the additional shelf with tools to work with the MPlay IPR? On it, you have a button to reload the scene only clicking on it.

I'm investigating the other issues. Let me check your scene again to see what happens.

Thanks,
-Juanjo
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2018_01_29-11_20_47.jpg
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Re: Alpha Channel display bug

Postby juanjgon » Mon Jan 29, 2018 10:45 am

juanjgon Mon Jan 29, 2018 10:45 am
I think that the problem with the particles color is related to your workflow. You are using at the same time an emissive material and you have enabled the Light Emission options in the OBJ spare parameters. Both lighting options must not be used at the same time. The Light Emission options in the spare parameters are designed to don't need to deal with emissive materials while building custom mesh light sources.

In your scene, I think that you only need to disable the Light Emission option and work only with the emissive material to avoid any problem, as you can see in the attached image.

Thanks,
-Juanjo
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2018_01_29-11_41_57.jpg
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Re: Alpha Channel display bug

Postby juanjgon » Mon Jan 29, 2018 11:12 am

juanjgon Mon Jan 29, 2018 11:12 am
I'm investigating the particles size issue and really I can't find any problem with this feature on your scene. The particles size is extracted from the "pscale" point attribute. If this attribute is not available the Default radius in the OBJ spare parameters is used.

The Radius global scale parameter also seems to work fine, as you can see in the attached images. Can you please check this issue again on your side? Be aware that you need to reload the scene to see the changes after modifying any OBJ spare parameter.

Thanks,
-Juanjo
Attachments
2018_01_29-12_09_12.jpg
2018_01_29-12_08_47.jpg
2018_01_29-12_08_29.jpg
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