[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Public WebGL] Weird alpha issue.



Holy crap!   I didn't expect *THAT*!

So - I make a super-simple "test-app" version of my game (in another
directory) and it produces white smoke where the main app generates
dark.  Next, I start to make my test application more and more like the
real application and the smoke stubbornly stays white (ie it looks the
same in Chrome as it does in Minefield).

Eventually, I have PRECISELY the same lines of code in the test-app and
the real-app - the same textures, the same shaders, the same absolutely
everything.  And they still look different!!    I have NO clue WTF is
making these two apps different.

Er...except for the HTML that hosts the web page has:

   <body bgcolor="#000000">        in the 'real application'
   <body>                                           in the 'test
application'

And lo and behold - when I change the HTML background color, the color
of the smoke changes!  So it looks like the problem is in the
compositing step.

I kinda suspect that I'm somehow getting a "destination alpha" frame
buffer in Minefield and no "destination alpha" in Chrome - so when I
write my translucent polygons into the frame buffer, I'm making the
resulting canvas have translucent bits!   Maybe that makes the
compositor blend in the HTML page's background wherever I write my
particles?

I'm doing more experiments.  I tried taking the SDK demo program
"sdk/demos/google/particles" and changing the HTML background to black -
but that didn't make a difference...so it's obviously a little more
complicated than just that.

Man - it's been about a decade since I last messed with destination
alpha!   I'm going to have to dust off my ancient copy of the "Red Book"
and try to kick my memory into life!

  -- Steve

-----------------------------------------------------------
You are currently subscribed to public_webgl@khronos.org.
To unsubscribe, send an email to majordomo@khronos.org with
the following command in the body of your email: