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  GradientPaint with Alpha Color: Broken in Java 7?  (Read 936 times)
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Offline Nyhm

Senior Member


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« Posted 2012-02-05 21:05:42 »
I recently added some gradient fill areas, just to polish up some interfaces. In cases where I was filling with translucent colors (Color objects created with alpha value), Java 6 runtime will fill the area with the proper gradient, and the area is translucent, as expected. Running the same code (compiled with Java 6) in a Java 7 runtime (on the same platform) behaves differently. The alpha-gradient areas are not transparent at all.

It appears that Java 7 will not honor the alpha byte of the Color objects when performing a GradientPaint fill. I've only tested this in Ubuntu, with Sun/Oracle Java runtimes.

I have not found any articles or bugs reported on this. I'm not well-versed in gradient painting, so can anyone clarify if this is a known issue (or if I'm doing it wrong)? I should code up a simple test case to demonstrate.

The quick work-around was to remove any alpha bytes from my gradient areas, so they paint consistently.
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Offline ra4king

JGO Kernel


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« Reply #1 - Posted 2012-02-05 21:29:32 »
Could you show us code? My game uses alpha gradient fill for the button highlight and it works fine in Java 7.
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Offline BoBear2681

JGO Coder


Medals: 18
« Reply #2 - Posted 2012-02-05 21:49:45 »
@ra4king, FYI, your game throws an NPE on startup.  Doesn't seem to affect anything though (I didn't actually play but title screen renders okay):

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java.lang.NullPointerException
   at com.ra4king.jdoodlejump.gui.a.p(Unknown Source)
   at com.ra4king.jdoodlejump.JDoodleJump.g(Unknown Source)
   at com.ra4king.a.e.f(Unknown Source)
   at com.ra4king.a.l.run(Unknown Source)
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Offline Nyhm

Senior Member


Medals: 3
Projects: 1


Island Forge
« Reply #3 - Posted 2012-02-05 21:58:09 »
Quote from: ra4king on 2012-02-05 21:29:32
Could you show us code?

Yep, I knew that would be the next question. This is pieced together a bit, but shows what I'm doing:

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int w = getWidth();
int h = getHeight();
Graphics2D g2 = (Graphics2D)g.create();
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
Color top = new Color(0,0,0,64);
Color bot = new Color(255,0,0,64);
GradientPaint gp = new GradientPaint(0,0,top,0,h,bot);
g2.setPaint(gp);
g2.fillRoundRect(0,0,w,h,8,8);


I have not yet tested this in isolation (need to make a test driver). Any insights welcome.
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Offline yuma

Junior Member


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Monkeys are listening
« Reply #4 - Posted 2012-02-05 22:03:41 »
Quote from: BoBear2681 on 2012-02-05 21:49:45
@ra4king, FYI, your game throws an NPE on startup.  Doesn't seem to affect anything though (I didn't actually play but title screen renders okay):

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java.lang.NullPointerException
   at com.ra4king.jdoodlejump.gui.a.p(Unknown Source)
   at com.ra4king.jdoodlejump.JDoodleJump.g(Unknown Source)
   at com.ra4king.a.e.f(Unknown Source)
   at com.ra4king.a.l.run(Unknown Source)



I have no problems playing it (except I have some pending grudge with xjump). Definitely no NPE here.
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Offline ra4king

JGO Kernel


Medals: 264
Projects: 2


I'm the King!
« Reply #5 - Posted 2012-02-05 23:37:47 »
That error is caused when trying to retrieve the list of cookies (the game stores your name and score in a local cookie). Looks like your browser didn't want to give it to me Smiley
However that whole area is surrounded with a try-catch so if it fails, it just prints the stack trace and returns quietly Smiley

Anyway, I tried your code on Windows 7 with Java 7 and Ubuntu with OpenJDK 7. I painted the background light green and then used your code: it worked fine. I could see the red tint on the bottom.

Either you're doing something wrong somewhere or your flavor of Linux is messed up Cheesy
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Offline Nyhm

Senior Member


Medals: 3
Projects: 1


Island Forge
« Reply #6 - Posted 2012-02-06 01:27:12 »
Thanks for running those tests, ra4king. In my context, the bad behavior is definitely triggered by the the alpha color. Maybe it's specific to my graphics card/driver (ATI Radeon / FGLRX driver).
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