我正在使用 BufferedGraphics 绘制一些东西,然后将其绘制到用户控件上。这是代码:
Private context As BufferedGraphicsContext
Private grafx As BufferedGraphics
Private Sub PaintDoc_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Me.SetStyle(ControlStyles.OptimizedDoubleBuffer, True)
Me.UpdateStyles()
context = BufferedGraphicsManager.Current
context.MaximumBuffer = New Size(Me.Width + 1, Me.Height + 1)
grafx = context.Allocate(Me.CreateGraphics, New Rectangle(0, 0, Me.Width, Me.Height))
grafx.Graphics.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBilinear
grafx.Graphics.PixelOffsetMode = Drawing2D.PixelOffsetMode.HighQuality
grafx.Graphics.SmoothingMode = Drawing2D.SmoothingMode.HighQuality
grafx.Graphics.Clear(Color.Transparent)
End Sub
Private Sub PaintDoc_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
If e.Button = Windows.Forms.MouseButtons.Left Then
grafx.Graphics.FillEllipse(New SolidBrush(DrawColorFinal), CInt(e.x - (BrushWidth / 2)), CInt(e.y - (BrushWidth / 2)), BrushWidth, BrushWidth)
Me.Invalidate()
End If
End Sub
Private Sub PaintDoc_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
grafx.Render(e.Graphics)
End Sub
问题是 grafx 没有像它所希望的那样透明背景,而是黑色背景。任何想法为什么?
更新:
感谢 Hans Passant,问题解决了,这里是最终代码,它也支持快速多层图像绘制:
Public Class PaintDoc
Public backBuffer(1) As Bitmap
Public bufferGraphics(1) As Graphics
Public layerIndex As Integer = 0
Private Sub PaintDoc_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Me.SetStyle(ControlStyles.OptimizedDoubleBuffer Or ControlStyles.UserPaint Or ControlStyles.AllPaintingInWmPaint, True)
Me.UpdateStyles()
For i As Integer = 0 To backBuffer.Length - 1
backBuffer(i) = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb)
bufferGraphics(i) = Graphics.FromImage(backBuffer(i))
bufferGraphics(i).InterpolationMode = Drawing2D.InterpolationMode.HighQualityBilinear
bufferGraphics(i).PixelOffsetMode = Drawing2D.PixelOffsetMode.HighQuality
bufferGraphics(i).SmoothingMode = Drawing2D.SmoothingMode.HighQuality
Next
End Sub
Private Sub PaintDoc_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
If e.Button = Windows.Forms.MouseButtons.Left Then
bufferGraphics(layerIndex).FillEllipse(New SolidBrush(DrawColorFinal), CInt(e.X - (BrushWidth / 2)), CInt(e.Y - (BrushWidth / 2)), BrushWidth, BrushWidth)
Me.Invalidate()
End If
End Sub
Private Sub PaintDoc_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
e.Graphics.Clear(Color.Transparent)
For i As Integer = 0 To backBuffer.Length - 1
e.Graphics.DrawImage(backBuffer(i), Point.Empty)
Next
End Sub
Private Sub PaintDoc_Resize(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Resize
For i As Integer = 0 To backBuffer.Length - 1
Dim newBuffer As Bitmap = New Bitmap(Me.ClientSize.Width, Me.ClientSize.Height, System.Drawing.Imaging.PixelFormat.Format32bppPArgb)
If backBuffer(i) IsNot Nothing Then
Using gr As Graphics = Graphics.FromImage(newBuffer)
gr.DrawImage(backBuffer(i), Point.Empty)
End Using
backBuffer(i) = Nothing
End If
backBuffer(i) = newBuffer
Next
End Sub
End Class