java - Algorithm to show n different shades of the same color in order of decreasing darkness -

the requirement follows:

we need map values colors. each discrete value have color.

we allow user specify maxcolor no mincolor allow them specify number of bins representing number of shades. if maxcolor selected color.green , bins= 5 ,then have 5 shades of green color selected max being darkest , rest 4 in order of increasing lightness.

//give me list of 5 shades of green first argument being darkest. list<color> greenshades = calculateshades(color.green,5);  //give me list of 7 shades of red first argument being darkest. list<color> greenshades = calculateshades(color.red,7); 

i tagged question java coding in java. understand algorithm.so implementation/idea of implementation in other languages javascript acceptable.

the basic concept revolves around idea of generating color based on fraction of source...

that is, if want 5 bands, each band 1/5 intensity of last...

public list<color> getcolorbands(color color, int bands) {      list<color> colorbands = new arraylist<>(bands);     (int index = 0; index < bands; index++) {         colorbands.add(darken(color, (double) index / (double) bands));     }     return colorbands;  }  public static color darken(color color, double fraction) {      int red = (int) math.round(math.max(0, color.getred() - 255 * fraction));     int green = (int) math.round(math.max(0, color.getgreen() - 255 * fraction));     int blue = (int) math.round(math.max(0, color.getblue() - 255 * fraction));      int alpha = color.getalpha();      return new color(red, green, blue, alpha);  } 

as quick , nasty example...

import java.awt.borderlayout; import java.awt.color; import java.awt.dimension; import java.awt.eventqueue; import java.awt.gridbagconstraints; import java.awt.gridbaglayout; import java.awt.insets; import java.awt.event.actionevent; import java.awt.event.actionlistener; import java.util.arraylist; import java.util.collections; import java.util.list; import javax.swing.jframe; import javax.swing.jpanel; import javax.swing.jscrollpane; import javax.swing.jslider; import javax.swing.timer; import javax.swing.uimanager; import javax.swing.unsupportedlookandfeelexception; import javax.swing.event.changeevent; import javax.swing.event.changelistener;  public class colorbands {      public static void main(string[] args) {         new colorbands();     }      public colorbands() {         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 testpane());                 frame.pack();                 frame.setlocationrelativeto(null);                 frame.setvisible(true);             }         });     }      public class testpane extends jpanel {          private jpanel bandspane;         private jslider slider;         private timer changetimer;          public testpane() {             bandspane = new jpanel(new gridbaglayout());             slider = new jslider(1, 100);             setlayout(new borderlayout());             add(new jscrollpane(bandspane));             add(slider, borderlayout.south);             slider.addchangelistener(new changelistener() {                 @override                 public void statechanged(changeevent e) {                     changetimer.restart();                 }             });              changetimer = new timer(250, new actionlistener() {                 @override                 public void actionperformed(actionevent e) {                     int bands = slider.getvalue();                     list<color> bandslist = getcolorbands(color.red, bands);                     bandspane.removeall();                     gridbagconstraints gbc = new gridbagconstraints();                     gbc.gridwidth = gridbagconstraints.remainder;                     gbc.insets = new insets(1, 1, 1, 1);                     (color color : bandslist) {                         bandspane.add(new colorband(color), gbc);                     }                     gbc.weighty = 1;                     bandspane.add(new jpanel(), gbc);                     revalidate();                     repaint();                 }             });             changetimer.setrepeats(false);             slider.setvalue(1);         }          @override         public dimension getpreferredsize() {             return new dimension(200, 200);         }     }      public list<color> getcolorbands(color color, int bands) {          list<color> colorbands = new arraylist<>(bands);         (int index = 0; index < bands; index++) {             colorbands.add(darken(color, (double) index / (double) bands));         }         return colorbands;      }      public static color darken(color color, double fraction) {          int red = (int) math.round(math.max(0, color.getred() - 255 * fraction));         int green = (int) math.round(math.max(0, color.getgreen() - 255 * fraction));         int blue = (int) math.round(math.max(0, color.getblue() - 255 * fraction));          int alpha = color.getalpha();          return new color(red, green, blue, alpha);      }      public class colorband extends jpanel {          public colorband(color color) {             setbackground(color);         }          @override         public dimension getpreferredsize() {             return new dimension(100, 20);         }      }  }