Draw Gradient in Java ME

Here is a J2ME class for gradients drawing, supporting both horizontal and vertical gradients.

This could be useful to substitute background gradient images with graphics drawn by code.

import javax.microedition.lcdui.Graphics;
 
public class Gradient
{
	public static final int VERTICAL = 0;
	public static final int HORIZONTAL = 1;
 
	public static void gradientBox(Graphics g, int color1, int color2, int left, int top, int width, int height, int orientation)
	{
		int max = orientation == VERTICAL ? height : width;
 
		int color1RGB[] = new int[]{(color1>>16) & 0xff,(color1>>8) & 0xff,color1 & 0xff};
		int color2RGB[] = new int[]{(color2>>16) & 0xff,(color2>>8) & 0xff,color2 & 0xff};
 
		int colorCalc[] = new int[]{
				(( color2RGB[0] - color1RGB[0] )<<16)/max,
				(( color2RGB[1] - color1RGB[1] )<<16)/max,
				(( color2RGB[2] - color1RGB[2] )<<16)/max
		};
 
		for(int i = max; i > -1; i--)
		{
 
			g.setColor(
					(color1RGB[0]+((i*colorCalc[0])>>16)) <<16 | 
					(color1RGB[1]+((i*colorCalc[1])>>16)) <<8  | 
					(color1RGB[2]+((i*colorCalc[2])>>16)) 	
					);
 
			if(orientation == VERTICAL)
				g.drawLine(left, top + i, left + width - 1, top + i);
			else
				g.drawLine(left + i, top, left + i, top + height - 1);
		}
	}
}

and here is a sample Canvas using the gradientBox method (the final effect is shown in the screenshot at beginning of this article):

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Graphics;
 
public class GradientRectCanvas extends Canvas {
 
	protected void paint(Graphics g)
	{
		int halfWidth = getWidth() / 2;
		int halfHeight = getHeight() / 2;
 
		Gradient.gradientBox(g, 0xffffff, 0xff0000, 0, 0, halfWidth, halfHeight, Gradient.HORIZONTAL);
 
		Gradient.gradientBox(g, 0xff0000, 0xffffff, halfWidth, 0, halfWidth, halfHeight, Gradient.VERTICAL);
 
		Gradient.gradientBox(g, 0xffff00, 0x00ffff, 0, halfHeight, halfWidth, halfHeight, Gradient.VERTICAL);
 
		Gradient.gradientBox(g, 0x00ff00, 0x0000ff, halfWidth, halfHeight, halfWidth, halfHeight, Gradient.VERTICAL);
	}
 
}

Article Metadata

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Code Example

Source file: Media:GradientRectMIDletSource.zip

Installation file: Media:GradientRectMIDletBinaries.zip

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Tested with

SDK: Nokia SDK 1.0 for Java

Devices(s): Nokia 7373, Nokia N82

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Compatibility

Platform(s): Series 40, Symbian

Device(s): MIDP2.0/CLDC 1.1

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Article

Keywords: Draw, Gradient, Canvas, Graphics

Created: jappit (11 Apr 2008)

Updated: tiviinik (16 Jan 2012)

Last edited: hamishwillee (23 Jan 2012)