Is "Blend Material" with a bitmap as a mask broke?

[RandellTrulson]

Hello everyone,

I've been using the blend material for a long time, even in Arnold.  However, after upgrading to Max 2024, when I make a blend material and I use a bitmap as the mask, it renders fine in the slate editor, no warnings from Arnold. 

However, when I go to render the scene, it gets to 5% and it locks up completely (Arnold GPU, 3090 RTX).  I have to go into "Task Manager" and kill 3DS Max.  Weirdly, it I pick something like, noise, checkerboard, or anything else besides a bitmap...it will render.   

I've tried changing from a bmp, to png, to tiff...same results.  I am wondering...is there an Arnold specific node I need to add between my mask image and the mask input of the "Blend Material"?

Thanks for your help in advance.

[wernienst]

No such problems here (RTX 2070, driver DCH 531.61). However, I found another issue: I cannot use nested Blend materials with Arnold GPU (CPU works).

[RandellTrulson · Accepted solution]

Ok, I found a solution to my problem, but there definitely is a bug in Arnold (GPU).  Here is how I can reproduce the issue.

• How this got started is I opened up an old scene make with ART. 
• I used the scene converter which made the materials into Arnold->Standard Surface ones.  
• As stated in the original message, it renders in the Slate editor fine, but when I go to render, it freezes up.  Even weirder is that if I use something other than a bitmap for the blend mask, it will render.  
• WORK AROUND : So, I rebuilt the same materials (approximately) but used "Physical Material", then it will render.    

Below is a screen capture of the two materials.  The one on the top is the remake using 2 "Physical Materials", and the one on the bottom is the one with 2 "Arnold Standard Surface" materials.  As you can see, they both render in the editor, but the bottom one ("Standard Surface") version will lock everything up where you have to kill the PID in task manager.  I even left it overnight thinking it might wake up, but the render was frozen at 5%.

I hope Arnold / Autodesk can use this to find out the issue.  Oh, and both materials have transparency, so that might play a role.  They are stupid simple materials, so the bug should be easy to find.  

[wernienst]

Again, no problem here, except that the gpu renderer ignores the rightmost Blend material. That is even more strange as in the material editor, which I've also set to gpu mode, it is rendered correctly.