Graphics & GDI+ Drawing

' --- Drawing on a PictureBox ---
Private Sub picBox_Paint(sender As Object, e As PaintEventArgs) Handles picBox.Paint
    Dim g As Graphics = e.Graphics
    g.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias   ' smooth curves

    ' Draw a red line
    Using pen As New Pen(Color.Red, 2)
        g.DrawLine(pen, 10, 10, 200, 10)
    End Using

    ' Fill a blue rectangle
    Using brush As New SolidBrush(Color.SteelBlue)
        g.FillRectangle(brush, 10, 30, 120, 60)
    End Using

    ' Draw a green circle (ellipse in square bounding box)
    Using pen As New Pen(Color.Green, 3)
        g.DrawEllipse(pen, 150, 30, 60, 60)
    End Using
End Sub

' --- Drawing on the Form itself ---
Private Sub Form1_Paint(...) Handles MyBase.Paint
    Dim g = e.Graphics
    ' draws directly on the form surface
End Sub

' --- Trigger a repaint (e.g. from a button click) ---
Private Sub btnDraw_Click(...) Handles btnDraw.Click
    picBox.Invalidate()   ' schedules Paint; does NOT draw immediately
End Sub

' --- WRONG — never store the Graphics object ---
' Dim g As Graphics = picBox.CreateGraphics()   ← erased on repaint!
' Use Invalidate() + Paint event instead.

' --- Clear the canvas ---
g.Clear(Color.White)   ' fill entire surface with White

Private Sub picBox_Paint(...) Handles picBox.Paint
    Dim g = e.Graphics
    g.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias

    ' --- Lines ---
    Using pen As New Pen(Color.Black, 1)
        g.DrawLine(pen, 10, 10, 200, 10)      ' horizontal
        g.DrawLine(pen, 10, 10, 10, 100)       ' vertical
        g.DrawLine(pen, 10, 10, 200, 100)      ' diagonal
    End Using

    ' Dashed line using DashStyle
    Using dashPen As New Pen(Color.Gray, 1)
        dashPen.DashStyle = Drawing2D.DashStyle.Dash
        g.DrawLine(dashPen, 10, 120, 200, 120)
    End Using

    ' --- Rectangles ---
    Using pen As New Pen(Color.Navy, 2)
        g.DrawRectangle(pen, 20, 20, 100, 60)   ' outline only
    End Using

    Using brush As New SolidBrush(Color.LightBlue)
        g.FillRectangle(brush, 140, 20, 100, 60) ' filled
    End Using

    ' Fill + outline
    Using brush As New SolidBrush(Color.Coral)
        g.FillRectangle(brush, 20, 100, 80, 40)
    End Using
    Using pen As New Pen(Color.DarkRed, 2)
        g.DrawRectangle(pen, 20, 100, 80, 40)   ' draw outline on top
    End Using

    ' Rounded rectangle (using GraphicsPath)
    Using path As New Drawing2D.GraphicsPath()
        Dim r = 12   ' corner radius
        path.AddArc(120, 100, r, r, 180, 90)
        path.AddArc(120 + 80 - r, 100, r, r, 270, 90)
        path.AddArc(120 + 80 - r, 100 + 40 - r, r, r, 0, 90)
        path.AddArc(120, 100 + 40 - r, r, r, 90, 90)
        path.CloseFigure()
        Using brush As New SolidBrush(Color.MediumPurple)
            g.FillPath(brush, path)
        End Using
    End Using
End Sub

' Ellipse: fits inside bounding rect (x, y, width, height)
g.DrawEllipse(New Pen(Color.Blue, 2), 10, 10, 150, 80)    ' outline
g.FillEllipse(New SolidBrush(Color.SkyBlue), 10, 10, 150, 80) ' filled

' Circle: width = height
g.FillEllipse(New SolidBrush(Color.Gold), 50, 50, 80, 80)   ' filled circle r=40

' Arc: part of an ellipse
' startAngle: 0=right, 90=bottom, 180=left, 270=top (clockwise)
' sweepAngle: degrees to sweep clockwise from startAngle
Using pen As New Pen(Color.Red, 3)
    g.DrawArc(pen, 10, 110, 100, 100, 0, 270)  ' ¾ of a circle
End Using

' Concentric circles (target / radar effect)
For r = 10 To 80 Step 20
    Dim cx = 120 : Dim cy = 100
    Using pen As New Pen(Color.FromArgb(255 - r * 2, 0, 120, 200), 2)
        g.DrawEllipse(pen, cx - r, cy - r, r * 2, r * 2)
    End Using
Next

' Progress ring (arc showing percentage)
Dim pct = 75
Dim sweep = 360 * pct \ 100
g.DrawArc(New Pen(Color.LimeGreen, 8), 20, 20, 80, 80, -90, sweep)  ' -90 starts at top

' --- Basic text ---
Using font  As New Font("Segoe UI", 14, FontStyle.Regular)
Using brush As New SolidBrush(Color.Black)
    g.DrawString("Hello, VB 2026!", font, brush, 10, 10)
End Using : End Using

' --- Bold, Italic, Underline ---
Using boldFont  As New Font("Arial", 12, FontStyle.Bold)
Using italFont  As New Font("Arial", 12, FontStyle.Italic)
Using underFont As New Font("Arial", 12, FontStyle.Underline)
Using brush     As New SolidBrush(Color.DarkBlue)
    g.DrawString("Bold",       boldFont,  brush, 10, 50)
    g.DrawString("Italic",     italFont,  brush, 10, 75)
    g.DrawString("Underline", underFont, brush, 10, 100)
End Using : End Using : End Using : End Using

' --- Centred text using MeasureString ---
Dim text = "Centred Title"
Using font  As New Font("Segoe UI", 16, FontStyle.Bold)
Using brush As New SolidBrush(Color.Navy)
    Dim sz = g.MeasureString(text, font)
    Dim x  = (picBox.Width  - sz.Width)  / 2
    Dim y  = (picBox.Height - sz.Height) / 2
    g.DrawString(text, font, brush, x, y)
End Using : End Using

' --- Text inside a rectangle with StringFormat ---
Dim rect As New Rectangle(10, 10, 200, 60)
Dim fmt  As New StringFormat()
fmt.Alignment     = StringAlignment.Center    ' horizontal
fmt.LineAlignment = StringAlignment.Center    ' vertical
Using font  As New Font("Segoe UI", 12)
Using brush As New SolidBrush(Color.White)
    g.FillRectangle(New SolidBrush(Color.SteelBlue), rect)
    g.DrawString("Vertically & Horizontally Centred", font, brush, rect, fmt)
End Using : End Using

' --- Triangle ---
Dim tri() = {
    New Point(100, 10),
    New Point(180, 130),
    New Point(20,  130)
}
g.FillPolygon(New SolidBrush(Color.LightGreen), tri)
g.DrawPolygon(New Pen(Color.DarkGreen, 2), tri)

' --- Regular hexagon (calculated with trig) ---
Dim cx = 150, cy = 100, radius = 60
Dim hex(5) As Point
For i = 0 To 5
    Dim angle = Math.PI * (2 * i - 1) / 6    ' 60° steps, flat-top orientation
    hex(i) = New Point(cx + CInt(radius * Math.Cos(angle)),
                        cy + CInt(radius * Math.Sin(angle)))
Next
g.FillPolygon(New SolidBrush(Color.SteelBlue), hex)

' --- Pie chart slices ---
' bounding rect: x=10, y=10, width=200, height=200
' Angles: 0° = 3-o'clock, clockwise. Use -90 to start at 12.
g.FillPie(New SolidBrush(Color.Red),    10, 10, 200, 200, -90, 108) ' 30%
g.FillPie(New SolidBrush(Color.Blue),   10, 10, 200, 200,  18, 144) ' 40%
g.FillPie(New SolidBrush(Color.Green),  10, 10, 200, 200, 162,  72) ' 20%
g.FillPie(New SolidBrush(Color.Orange), 10, 10, 200, 200, 234,  36) ' 10%

' Exploded slice (offset one slice from the centre)
Dim explodeDist = 12
Dim midAngle    = Math.PI * (-90 + 108 / 2) / 180   ' midpoint of first slice
Dim offX = CInt(explodeDist * Math.Cos(midAngle))
Dim offY = CInt(explodeDist * Math.Sin(midAngle))
g.FillPie(New SolidBrush(Color.Red), 10 + offX, 10 + offY, 200, 200, -90, 108)

Imports System.Drawing.Drawing2D

' --- Horizontal gradient ---
Using lgb As New LinearGradientBrush(
        New Point(0, 0), New Point(200, 0),
        Color.DodgerBlue, Color.MediumPurple)
    g.FillRectangle(lgb, 10, 10, 200, 50)
End Using

' --- Vertical gradient ---
Using lgb As New LinearGradientBrush(
        New Point(0, 0), New Point(0, 80),
        Color.Orange, Color.OrangeRed)
    g.FillRectangle(lgb, 10, 80, 200, 80)
End Using

' --- Diagonal gradient ---
Using lgb As New LinearGradientBrush(
        New Point(230, 0), New Point(430, 170),
        Color.LimeGreen, Color.Navy)
    g.FillEllipse(lgb, 230, 10, 180, 160)
End Using

' --- Transparent overlay ---
Using brush As New SolidBrush(Color.FromArgb(120, Color.Red))
    g.FillEllipse(brush, 60, 20, 100, 100)   ' 47% opaque
End Using

' --- PathGradientBrush: radial from centre ---
Dim pts() = {New Point(150,10), New Point(250,80),
              New Point(200,160), New Point(100,160),
              New Point(50,80)}
Using pgb As New PathGradientBrush(pts)
    pgb.CenterColor     = Color.White
    pgb.SurroundColors  = {Color.DodgerBlue}
    g.FillPolygon(pgb, pts)
End Using