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Revision as of 01:05, 23 January 2012 by hamishwillee (Talk | contribs)

Draw Gradient in Java ME

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

J2me gradients.jpg

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
Code ExampleTested with
Devices(s): Nokia 7373, Nokia N82
Compatibility
Platform(s): Series 40, Symbian
Series 40
Symbian
S60 3rd Edition FP2
Device(s): MIDP2.0/CLDC 1.1
Article
Keywords: Draw, Gradient, Canvas, Graphics
Created: jappit (11 Apr 2008)
Updated: tiviinik (16 Jan 2012)
Last edited: hamishwillee (23 Jan 2012)
321 page views in the last 30 days.