I did some bit of uneducated debugging.

It seems there is something going on with the GL/GLX and alpha bits.

The LWJGL code is creating a GLX window for its content.

I noticed that the screen displaying the logo on startup was entirely
translucent, without the 256x256 block in the lower left corner that is
not translucent later on.

Changing a "glClearColor(0, 0, 0, 0);" to "glClearColor(0, 0, 0, 1);"
makes the logo screen not translucent (and any value between 0 and 1 for
the alpha value makes it somewhere in-between). - i.e. using
glClearColor(0, 0, 0, 1); makes at least the logo screen look the way it
should be!

Now, it seems Minecraft is only using that code path for the logo and
not for the rest of the game. Now I am wondering if "0" for the alpha
means translucend and "1" means solid or if it's supposed to be the
other way around.

Also, I am wondering if the game is expecting that the alpha value on
the window has any meaning at all or if there is some hidden flag
somewhere that tells the compositing manager what to do with that alpha
bit and something is wrong in there. (?)

Maybe Minecraft/LWJGL  is selecting a visual where it expects the alpha
bit to be ignored and chooses the wrong one - but this is a random guess
as I really don't know much about GLX and the setup procedure of
windows/visuals and how the alpha information is passed down to the
compositor.

Maybe someone with more knowledge could point me into the right
direction...

-- 
You received this bug notification because you are a member of Ubuntu-X,
which is subscribed to xserver-xorg-video-intel in Ubuntu.
https://bugs.launchpad.net/bugs/1277905

Title:
  Game windows (minecraft, titan attacks, maybe others) on Intel are
  transparent and no longer playable

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1277905/+subscriptions

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