GradientPaint with Alpha Color: Broken in Java 7?

Newbie & Debugging Questions
#1

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.

#2

Could you show us code? My game uses alpha gradient fill for the button highlight and it works fine in Java 7.

#3

@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):


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)
#4

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


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.

#5

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

#6

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 :slight_smile:
However that whole area is surrounded with a try-catch so if it fails, it just prints the stack trace and returns quietly :slight_smile:

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 :smiley:

#7

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).