I spent a lot of time trying to find/create a blending algorithm that worked for me, this is basically what I was able to hobble together.
I've used this approach to generate a gradient transition mixing multiple colors, as demonstrated here
Basically, this approach allows you to set up a series of colors and percentage marks so that you gain much greater control over which points the colors transition between.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.text.NumberFormat;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class ColorFading {
public static void main(String[] args) {
new ColorFading();
}
public ColorFading() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new FadePane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class FadePane extends JPanel {
private final float[] fractions = new float[]{0f, 0.5f, 1f};
private final Color[] colors = new Color[]{Color.RED, Color.YELLOW, Color.GREEN};
private float progress = 1f;
private JSlider slider;
public FadePane() {
slider = new JSlider(0, 100);
setLayout(new BorderLayout());
add(slider, BorderLayout.SOUTH);
slider.addChangeListener(new ChangeListener() {
@Override
public void stateChanged(ChangeEvent e) {
progress = ((float)slider.getValue() / 100f);
repaint();
}
});
slider.setValue(100);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
int width = getWidth();
int height = getHeight();
Color startColor = blendColors(fractions, colors, progress);
g2d.setColor(startColor);
g2d.fillRect(0, 0, width, height);
g2d.dispose();
}
}
public static Color blendColors(float[] fractions, Color[] colors, float progress) {
Color color = null;
if (fractions != null) {
if (colors != null) {
if (fractions.length == colors.length) {
int[] indicies = getFractionIndicies(fractions, progress);
float[] range = new float[]{fractions[indicies[0]], fractions[indicies[1]]};
Color[] colorRange = new Color[]{colors[indicies[0]], colors[indicies[1]]};
float max = range[1] - range[0];
float value = progress - range[0];
float weight = value / max;
color = blend(colorRange[0], colorRange[1], 1f - weight);
} else {
throw new IllegalArgumentException("Fractions and colours must have equal number of elements");
}
} else {
throw new IllegalArgumentException("Colours can't be null");
}
} else {
throw new IllegalArgumentException("Fractions can't be null");
}
return color;
}
public static int[] getFractionIndicies(float[] fractions, float progress) {
int[] range = new int[2];
int startPoint = 0;
while (startPoint < fractions.length && fractions[startPoint] <= progress) {
startPoint++;
}
if (startPoint >= fractions.length) {
startPoint = fractions.length - 1;
}
range[0] = startPoint - 1;
range[1] = startPoint;
return range;
}
public static Color blend(Color color1, Color color2, double ratio) {
float r = (float) ratio;
float ir = (float) 1.0 - r;
float rgb1[] = new float[3];
float rgb2[] = new float[3];
color1.getColorComponents(rgb1);
color2.getColorComponents(rgb2);
float red = rgb1[0] * r + rgb2[0] * ir;
float green = rgb1[1] * r + rgb2[1] * ir;
float blue = rgb1[2] * r + rgb2[2] * ir;
if (red < 0) {
red = 0;
} else if (red > 255) {
red = 255;
}
if (green < 0) {
green = 0;
} else if (green > 255) {
green = 255;
}
if (blue < 0) {
blue = 0;
} else if (blue > 255) {
blue = 255;
}
Color color = null;
try {
color = new Color(red, green, blue);
} catch (IllegalArgumentException exp) {
NumberFormat nf = NumberFormat.getNumberInstance();
System.out.println(nf.format(red) + "; " + nf.format(green) + "; " + nf.format(blue));
exp.printStackTrace();
}
return color;
}
}