Re: "fading" graphics using Graphics2D

visionset wrote:
"Brandon McCombs" <none@xxxxxxxx> wrote in message news:46552116$0$4719$4c368faf@xxxxxxxxxxxxxxxxx
Hello everyone,

I started a small Java program just as something fun to do. It simulates a sonar, like on a submarine. Right now I'm at the point where I have multiple objects moving independently around the sonar screen with a rotating needle. I keep track of the speed/location/etc. of each object which extends Thread. The needle rotates around the screen in a way that lights up the part it just touched and the glow gradually fades away using a gradient that I created. The objects on the screen only change location when the needle intersects them (using the intersects() method of java.awt.geom.Line2D.Double).
...

I think you are on the right track with the transparency overlay.
I would paint a rectangle of eg new Color(1.0,1.0,1.0,alpha) over the icon.
also use a Swing Timer that starts when the icon is first created (needle pass over).

Actually I already have a Timer that runs the entire time the program runs. It fires every 6 ms and does all the repainting by calling repaint() in actionPerformed(). Shortly after posting this I ended up fixing the problem in the code where the object wasn't disappearing when it moved out of range and I inadvertently laid the groundwork for fixing the fading of the objects. I had the revelation for fixing the fading while laying in bed later that night and tried it first thing Friday morning and got it working.

I had setup multiple "if" conditions for drawing or not drawing the objects. As my last condition, which is encountered when the object is in range but isn't being intersected by the needle, I ended up creating/calling a variation of each object's display() method which draws the object with increasing transparency, in effect making it fade away. With each object tracking its own transparency I was able to make them all fade properly based on their distance from the needle. The first condition, when the object is both in range and intersected by the needle, calls the primary variation of the object's display() method which will redraw the object and its label with 0 transparency thus making it appear again (as I timed the fading of each object so that the object totally disappears right before the needle rotates back around to intersect it again).

Then every actionPerformed will increase decrease the alpha.
You are going to need to repaint regularly perhaps by another timer purely for repainting.

See above. I already had that in place. I have 1 timer that repaints everything in varying layers. The moving vehicles that are tracked on the sonar are in the top-most layer.

If your app does other intensive stuff you will likely need to make some drawing optimisations
such as calling repaint(x,y,w,h) to only repaint the areas necessary, eg icons with attendent rectangles that are not fully opaque. You would union together the rectangles to obtain the reapaint area.

Since I'm increasingly using more transparencies I'm going to have to think of ways to optimize it because it is using more and more CPU to run the program (mainly to repaint I believe). I'll look into your idea to see if I can get repainting only certain areas to work.

Cache everything that is going to be painted.

Just some ideas,
HTH,

thanks for your help Mike.
.