Mixed Blending in GDI+

This article has been excerpted from book "Graphics Programming with GDI+".

Mixed blending is a combination of both alpha blending and color blending. It is useful when you need to draw transparent and blended graphics shapes, for example, drawing a transparent image with transparent shapes using a blended linear gradient brush.

Listing 9.34 shows how to mix these two types of blending. Using the InterpolationColors property, we create a LinearGradientBrush object and set its Colors and Positions properties to specify the blending colors and positions. After that we create a Bitmap object and apply a color matrix using SetColorMatrix. Then we draw a rectangle and an ellipse and we call DrawImage.

LISTING 9.34: Mixed blending example

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Mixed_Blending_in_GDI_
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            g.Clear(this.BackColor);

            // Create a LinearGradientBrush object
            LinearGradientBrush brBrush = new LinearGradientBrush(
            new Point(0, 0), new Point(50, 20),
            Color.Blue, Color.Red);
            Rectangle rect =
            new Rectangle(20, 20, 200, 100);

            // Create color and points arrays
            Color[] clrArray =
{
Color.Red, Color.Blue, Color.Green,
Color.Pink, Color.Yellow,
Color.DarkTurquoise
};

            float[] posArray =
{
0.0f, 0.2f, 0.4f,
0.6f, 0.8f, 1.0f
};

            // Create a ColorBlend object and set its Colors and Positions properties
            ColorBlend colorBlend = new ColorBlend();
            colorBlend.Colors = clrArray;

            // Set InterpolationColors = colorBlend;
            // Create a Bitmap object from a file
            Bitmap bitmap = new Bitmap("MyPhoto.jpg");

            // Create a points array
            float[][] ptsArray =
{
new float[] {1,0,0,0,0},
new float[] {0,1,0,0,0},
new float[] {0,0,1,0,0},
new float[] {0,0,0,0.5f,0},
new float[] {0,0,0,0,1}
};

            // Create a ColorMtrix object using pts array
            ColorMatrix clrMatrix =
            new ColorMatrix(ptsArray);

            // Create an ImageAttributes object
            ImageAttributes imgAttributes =
            new ImageAttributes();

            // Set color matrix of ImageAttributes
            imgAttributes.SetColorMatrix(clrMatrix,
            ColorMatrixFlag.Default,
            ColorAdjustType.Bitmap);

            // Fill rectangle
            g.FillRectangle(brBrush, rect);
            rect.Y += 120;

            // Fill ellipse
            g.FillEllipse(brBrush, rect);

            // Draw image using ImageAttributes
            g.DrawImage(bitmap,
            new Rectangle(0, 0, bitmap.Width, bitmap.Height),
            0, 0, bitmap.Width, bitmap.Height,
            GraphicsUnit.Pixel, imgAttributes);

            // Dispose of objects
            brBrush.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }
}



FIGURE 9.46: A mixed blending example

Figure 9.46 shows the output from Listing 9.34. The rectangle and ellipse are blended (multicolor) and translucent (alpha-blended).

Conclusion

Hope the article would have helped you in understanding Mixed Blending in GDI+. Read other articles on GDI+ on the website.

This book teaches .NET developers how to work with GDI+ as they develop applications that include graphics, or that interact with monitors or printers. It begins by explaining the difference between GDI and GDI+, and covering the basic concepts of graphics programming in Windows.