10 basic skills for GDI+ programming in C# 2

5. Gradient color filling

You need to use two brushes:

LinearGradientBrush(LinearGradientBrush)

PathGuadientBrush(PathGuadientBrush)

private void button4_Click(object sender,System.EventArgs e)

{

/ /Drawing surface

Graphics g =this.pictureBoxII1.CreateGraphics();

g.FillRectangle(Brushes.White,this.pictureBoxII1.ClientRectangle);

//Define a linear gradient brush

LinearGradientBrush lgbrush =

new LinearGradientBrush(

new Point(0, 10),

new Point(150, 10),

Color.FromArgb(255, 0, 0),

Color.FromArgb(0, 255, 0));

Pen pen = new Pen(lgbrush);

//Draw a straight segment with a linear brush gradient effect pen and fill a rectangle

g.DrawLine(pen, 10, 130, 500, 130);

g.FillRectangle(lgbrush, 10, 150, 370, 30);

//Define the path and add an ellipse

GraphicsPath gp = new GraphicsPath();

gp.AddEllipse(10, 10, 200, 100) ;

//Use this path to define the path gradient brush

PathGradientBrush brush =

new PathGradientBrush(gp);

//Color array

Color[] colors = {

Color.FromArgb(255, 0, 0 ),

Color.FromArgb(100, 100, 100),

Color.FromArgb(0, 255, 0),

Color.FromArgb(0, 0, 255)};

//Define color gradient ratio

float[] r = {0.0f, 0.3f, 0.6f, 1.0f};

ColorBlend blend = new ColorBlend();

blend.Colors = colors;

blend.Positions = r;

brush .InterpolationColors = blend;

//Fill a rectangle outside the ellipse

g.FillRectangle(brush, 0, 0, 210, 110);

//Define a second path gradient brush with the path added to the ellipse

GraphicsPath gp2 = new GraphicsPath();

gp2.AddEllipse(300, 0, 200, 100);

PathGradientBrush brush2 = new PathGradientBrush(gp2);

//Set the center point position and color

brush2. CenterPoint = new PointF(450, 50);

brush2.CenterColor = Color.FromArgb(0, 255, 0);

//Set the border color

Color[] color2 = {Color.FromArgb(255, 0, 0)};

brush2.SurroundColors = color2;

//Use the second gradient brush to fill the ellipse

g.FillEllipse(brush2, 300, 0, 200, 100);

}

6, GDI+ Coordinate system

Universal coordinate system - user-defined coordinate system.

Page coordinate system - virtual coordinate system.
Device coordinate system - screen coordinate system.

When the units of the page coordinate system and the device coordinate system are both pixels, they are the same.

private void button10_Click(object sender, System.EventArgse)

{

Graphics g = this.pictureBoxII1.CreateGraphics();

g.Clear(Color.White);

this.Draw(g);

}

private void Draw(Graphics g)

{

g.DrawLine(Pens.Black, 10, 10, 100, 100);

g.DrawEllipse(Pens.Black, 50, 50, 200, 100);

g.DrawArc(Pens.Black, 100, 10, 100, 100, 20, 160);

g.DrawRectangle(Pens.Green, 50, 200, 150, 100);

}

private void button5_Click(object sender, System.EventArgs e)

{

//Shift left

Graphics g = this.pictureBoxII1.CreateGraphics();

g.Clear(Color.White);

g. TranslateTransform(-50, 0);

this.Draw(g);

}

private void button6_Click(object sender, System.EventArgs e)

{

//Shift right

Graphics g = this .pictureBoxII1.CreateGraphics();

g.Clear(Color.White);

g.TranslateTransform(50, 0);

this.Draw(g);

}

private void button7_Click(object sender , System.EventArgs e)

{

//Rotate

Graphics g = this.pictureBoxII1.CreateGraphics();

g.Clear(Color.White);

g.RotateTransform(-30);

this.Draw(g);

}

private void button8_Click(object sender, System.EventArgs e)

{

//Enlarge

Graphics g = this.pictureBoxII1.CreateGraphics();

g. Clear(Color.White);

g.ScaleTransform(1.2f, 1.2f);

this.Draw(g);

}

private void button9_Click(object sender, System.EventArgs e)

{

//Reduce

Graphics g = this.pictureBoxII1.CreateGraphics();

g.Clear(Color.White);

g.ScaleTransform(0.8f, 0.8f);

this.Draw(g) ;

}

7. Global coordinates - transformation will have an impact on every primitive on the drawing surface. Usually used to set a universal coordinate system.

The following program moves the original fixed point to the center of the control, and the Y-axis is facing upward.

//First draw a circle

Graphics g = e.Graphics;

g.FillRectangle(Brushes.White, this.ClientRectangle);

g.DrawEllipse(Pens.Black, -100, -100, 200, 200);

//To make the y-axis point forward, it must be mirrored relative to the x-axis

//The transformation matrix is ​​[1,0,0,-1,0,0]

Matrix mat = new Matrix(1, 0, 0, -1, 0, 0);

g.Transform = mat;

Rectangle rect = this.ClientRectangle;

int w = rect.Width;

int h = rect.Height ;

g.TranslateTransform(w/2, -h/2);

//With the origin as the center, make a circle with a radius of 100

g.DrawEllipse(Pens.Red, -100, -100, 200, 200);
g.TranslateTransform(100, 100);

g.DrawEllipse(Pens.Green, -100, -100, 200, 200);

g.ScaleTransform(2, 2);

g.DrawEllipse(Pens.Blue, -100, -100, 200, 200 );

8. Local coordinate system - only certain graphics are transformed, while other graphic elements remain unchanged.

protected override void OnPaint(PaintEventArgs e)

{

Graphics g = e.Graphics;

//The client area is set to white

g.FillRectangle(Brushes.White, this.ClientRectangle);

/ /y axis is facing up

Matrix mat = new Matrix(1, 0, 0, -1, 0, 0);

g.Transform = mat;

//Move the coordinate origin to the center of the form

Rectangle rect = this.ClientRectangle;

int w = rect.Width;

int h = rect.Height;

g.TranslateTransform(w/2, -h/2);

//Draw an ellipse in global coordinates

g.DrawEllipse(Pens.Red, -100, -100, 200, 200);

g.FillRectangle(Brushes.Black, -108, 0, 8, 8);

g.FillRectangle(Brushes.Black, 100, 0, 8, 8);

g.FillRectangle(Brushes.Black, 0, 100, 8, 8);

g.FillRectangle(Brushes.Black, 0, -108, 8, 8);

//Create an ellipse and transform it in the local coordinate system

GraphicsPath gp = new GraphicsPath();

gp.AddEllipse(-100, -100, 200, 200);

Matrix mat2 = new Matrix() ;

//Translation

mat2.Translate(150, 150);

//Rotation

mat2.Rotate(30);

gp.Transform(mat2);

g.DrawPath(Pens.Blue, gp);

PointF[] p = gp.PathPoints;

g.FillRectangle(Brushes.Black, p[0].X-2, p[0].Y+2, 4, 4);

g.FillRectangle(Brushes.Black, p[3].X-2, p[3].Y+2, 4, 4);

g.FillRectangle(Brushes.Black, p[6].X-4, p[6].Y-4, 4, 4);

g.FillRectangle(Brushes.Black, p[9].X-4, p[9].Y-4, 4, 4);
gp. Dispose();
//base.OnPaint (e);

}

9. Alpha blending

The A of Color.FromArgb() is Alpha. Alpha values ​​range from 0 to 255. 0 means completely transparent and 255 means completely opaque.

Current color = foreground color×alpha/255+background color×(255-alpha)/255

protected override void OnPaint(PaintEventArgs e)

{

Graphics g = e.Graphics;

// Create a filled rectangle

SolidBrush brush = new SolidBrush(Color.BlueViolet);

g.FillRectangle(brush, 180, 70, 200, 150);

//Create a bitmap between two bitmaps Has transparency effect

Bitmap bm1 = new Bitmap(200, 100);

Graphics bg1 = Graphics.FromImage(bm1);

SolidBrush redBrush =

new SolidBrush(Color.FromArgb(210, 255, 0, 0) );

SolidBrush greenBrush =

new SolidBrush(Color.FromArgb(210, 0, 255, 0));

bg1.FillRectangle(redBrush, 0, 0, 150, 70);

bg1.FillRectangle(greenBrush , 30, 30, 150, 70);

g.DrawImage(bm1, 100, 100);

//Create a bitmap with no transparency effect between the two bitmaps

Bitmap bm2 = new Bitmap( 200, 100); aGraphics BG2 = Graphics.fromimage (BM2); 0, 170); gBg2.fillrectangle ( greenBrush, 30, 30, 150, 70);

g.CompositingQuality = CompositingQuality.GammaCorrected;

g.DrawImage(bm2, 300, 200);

//base.OnPaint (e);

}

10. Anti-aliasing

protected override void OnPaint(PaintEventArgs e)

{

Graphics g = e.Graphics;

//Enlarge 8 times

g.ScaleTransform(8, 8);

// No anti-aliasing graphics and text

Draw(g);

//Set anti-aliasing

g.SmoothingMode = SmoothingMode.AntiAlias;

//Shift right by 40

g.TranslateTransform(40, 0) ;

//Drawing is after anti-aliasing

Draw(g);

//base.OnPaint (e);

}

private void Draw(Graphics g)

{

//Draw graphics and text

g.DrawLine(Pens.Gray, 10, 10, 40, 20);

g.DrawEllipse(Pens.Gray, 20, 20, 30, 10);

string s = "Anti-aliasing test" ;

Font font = new Font("宋体", 5);

SolidBrush brush = new SolidBrush(Color.Gray);

g.DrawString(s, font, brush, 10, 40);

}

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