Calculates a color by applying the specified alpha value to the specified front color. - CSharp System.Drawing

CSharp examples for System.Drawing:Color

  1. HOME
  2. CSharp
  3. System.Drawing
  4. Color

Description

Calculates a color by applying the specified alpha value to the specified front color.

Demo Code


using System.Drawing;

public class Main{
        ///-------------------------------------------------------------------------------------
      /// <summary>
      /// Calculates a color by applying the specified alpha value to the specified front
      /// color, assuming the color behind the front color is the specified back color. The
      /// returned color has the alpha channel set to completely opaque, but whose alpha
      /// channel value appears to be the one specified.
      /// </summary>
      ///-------------------------------------------------------------------------------------
      public static Color CalculateColor(Color front, Color back, int alpha)
      {/*w ww  . j  a  v a2  s .  c  o m*/
         // Use alpha blending to brigthen the colors but don't use it
         // directly. Instead derive an opaque color that we can use.
         // -- if we use a color with alpha blending directly we won't be able 
         // to paint over whatever color was in the background and there
         // would be shadows of that color showing through
         Color frontColor = Color.FromArgb(255, front);
         Color backColor = Color.FromArgb(255, back);

         float frontRed = frontColor.R;
         float frontGreen = frontColor.G;
         float frontBlue = frontColor.B;
         float backRed = backColor.R;
         float backGreen = backColor.G;
         float backBlue = backColor.B;

         float fRed = frontRed * alpha / 255 + backRed * ((float)(255 - alpha) / 255);
         byte newRed = (byte)fRed;
         float fGreen = frontGreen * alpha / 255 + backGreen * ((float)(255 - alpha) / 255);
         byte newGreen = (byte)fGreen;
         float fBlue = frontBlue * alpha / 255 + backBlue * ((float)(255 - alpha) / 255);
         byte newBlue = (byte)fBlue;

         return Color.FromArgb(255, newRed, newGreen, newBlue);
      }
}

Related Tutorials