Namespaces

Variants
Actions

Please note that as of October 24, 2014, the Nokia Developer Wiki will no longer be accepting user contributions, including new entries, edits and comments, as we begin transitioning to our new home, in the Windows Phone Development Wiki. We plan to move over the majority of the existing entries over the next few weeks. Thanks for all your past and future contributions.

Revision as of 04:00, 8 August 2013 by hamishwillee (Talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

How to create a color fading text in Java ME

From Wiki
Jump to: navigation, search
Article Metadata
Code ExampleArticle
Created: jappit (18 Jun 2008)
Last edited: hamishwillee (08 Aug 2013)

We'll implement a simple class to draw text that changes multiple colors with a fading effect.
You can view it in action here.
J2me color fade text.gif
So, let's start defining our ColorFadeText class.

Source code: ColorFadeText class

We start defining the necessary properties:

//will hold the colors to fade
int[] colors = null;
 
//duration of a single fade
int fadeDuration = 0;
 
//effect start time
long startTime = 0;
 
//property used to check if effect has started
public boolean started = false;
 
//the text to be drawn
String text = null;

Now, we define the main constructor, that will accept the following arguments:

  • the text to be drawn
  • an int[] array containing the colors to fade into
  • the duration of a single fade
public ColorFadeText(String text, int[] colors, int fadeDuration)
{
if(colors.length == 0)
{
throw new IllegalArgumentException("You must define at least 1 color");
}
this.text = text;
this.colors = colors;
this.fadeDuration = fadeDuration;
}

The effect start() method will simply set the startTime value to current time and the started property to true

public void start()
{
startTime = System.currentTimeMillis();
 
started = true;
}

Then, we have the paint() method, that will be used to paint the text on the given Graphics instance:

public void paint(Graphics g, int x, int y, int anchor)
{
if(started)
{
long diff = System.currentTimeMillis() - startTime;
 
int module = (int)(diff % fadeDuration);
 
int colorIndex = (int)(diff / fadeDuration) % colors.length;
 
int midColor = midColor(
colors[(colorIndex + 1) % colors.length],
colors[colorIndex],
module,
fadeDuration
);
 
g.setColor(midColor);
}
else
{
g.setColor(colors[0]);
}
 
g.drawString(text, x, y, anchor);
}

The following utility method will be the one actually used to get the current text color:

static int midColor(int color1, int color2, int prop, int max)
{
int red =
(((color1 >> 16) & 0xff) * prop +
((color2 >> 16) & 0xff) * (max - prop)) / max;
 
int green =
(((color1 >> 8) & 0xff) * prop +
((color2 >> 8) & 0xff) * (max - prop)) / max;
 
int blue =
(((color1 >> 0) & 0xff) * prop +
((color2 >> 0) & 0xff) * (max - prop)) / max;
 
int color = red << 16 | green << 8 | blue;
 
return color;
}

How to use it?

Using the ColorFadeText object is quite simple, since it'll be very similar to use a common String. Just follow this plain steps.

1. Create a ColorFadeText instance

ColorFadeText text = new ColorFadeText(
"I'M A FADING TEXT!",
new int[]{0xff0000, 0x00ff00, 0x0000ff, 0xff00ff},
1000
);

2. Start it...

text.start();

3. Paint it, using the same arguments used by Graphics drawString() method (adding a reference to the Graphics instance):

text.paint(g,
getWidth() / 2,
2,
Graphics.HCENTER | Graphics.TOP
);

Just a side note: since it's an animated effect, you'll need to repaint it quite frequently, so, for example, you can use a Thread to periodically call Canvas repaint() method.

Source code download

You can download source code of ColorFadeText, together with a sample Canvas that makes use of it, here: Color Fading sources

This page was last modified on 8 August 2013, at 04:00.
79 page views in the last 30 days.

Was this page helpful?

Your feedback about this content is important. Let us know what you think.

 

Thank you!

We appreciate your feedback.

×