问题
I have a picture box that will be showing an image. I want the user to be able to click, drag, and mouse up to a rectangle on the image. Like "I want to do something using this rectangle I drew here on this picture". If they click again, I want the previous rectangle to disappear and they start over or when I click a button to clear the highlighting rectangle they drew.
So I did find some good starting code from the msdn example about creating a zoom in rubber band rectangle that I edited a bit below, but I'm having some issues with:
Public bHaveMouse As Boolean
Public ptOriginal As Point
Public ptLast As Point
Public rect As Rectangle
Public b_Redraw As Boolean = False
' and Normalize the points and draw the reversible frame.
Private Sub MyDrawReversibleRectangle(ByVal p1 As Point, ByVal p2 As Point)
Try
'clear
' Convert the points to screen coordinates.
p1 = PointToScreen(p1)
p2 = PointToScreen(p2)
' Normalize the rectangle.
If (p1.X < p2.X) Then
rect.X = p1.X
rect.Width = p2.X - p1.X
Else
rect.X = p2.X
rect.Width = p1.X - p2.X
End If
If (p1.Y < p2.Y) Then
rect.Y = p1.Y
rect.Height = p2.Y - p1.Y
Else
rect.Y = p2.Y
rect.Height = p1.Y - p2.Y
End If
If rect.Width > pbZoneImage.Width Then
rect.Width = pbZoneImage.Width
End If
If rect.Height > pbZoneImage.Height Then
rect.Height = pbZoneImage.Height
End If
' Draw the reversible frame.
ControlPaint.DrawReversibleFrame(rect, Color.Red, FrameStyle.Thick)
Catch ex As Exception
End Try
End Sub
Private Sub pbZoneImage_MouseDown(sender As Object, e As MouseEventArgs) Handles pbZoneImage.MouseDown
If e.Button <> Windows.Forms.MouseButtons.Left Then
Exit Sub
End If
Try
' Make a note that we "have the mouse".
bHaveMouse = True
' Store the "starting point" for this rubber-band rectangle.
If b_Redraw Then
If (ptLast.X <> -1) Then
' Dim ptCurrent As Point
'ptCurrent.X = e.X
'ptCurrent.Y = e.Y
MyDrawReversibleRectangle(ptOriginal, ptLast)
End If
' Set flags to know that there is no "previous" line to reverse.
ptLast.X = -1
ptLast.Y = -1
ptOriginal.X = -1
ptOriginal.Y = -1
End If
ptOriginal.X = e.X
ptOriginal.Y = e.Y
' Special value lets us know that no previous
' rectangle needs to be erased.
ptLast.X = -1
ptLast.Y = -1
Catch ex As Exception
End Try
End Sub
Private Sub pbZoneImage_MouseMove(sender As Object, e As MouseEventArgs) Handles pbZoneImage.MouseMove
Dim ptCurrent As Point
ptCurrent.X = e.X
ptCurrent.Y = e.Y
' If we "have the mouse", then we draw our lines.
If (bHaveMouse) Then
' If we have drawn previously, draw again in
' that spot to remove the lines.
If (ptLast.X <> -1) Then
MyDrawReversibleRectangle(ptOriginal, ptLast)
End If
' Update last point.
ptLast = ptCurrent
' Draw new lines.
MyDrawReversibleRectangle(ptOriginal, ptCurrent)
End If
End Sub
Private Sub pbZoneImage_MouseUp(sender As Object, e As MouseEventArgs) Handles pbZoneImage.MouseUp
'Try
' ' Set internal flag to know we no longer "have the mouse".
bHaveMouse = False
End Sub
My Problem: Sometimes when drawing it doesn't remove the previously drawn rectangle, or if I hover over certain buttons (like the exit button) the rectangles disappear! I want they to stay so that I can record the start and end point of the rectangle for other programs. I want them to disappear when I hit my clear rectangle button, but I feel like I am getting confused on something that should be very simple.
Another issue is I'm trying to keep the rectangle from spilling outside the picture box (Pbzoneimage). But it does, and changes color.
Where did I go wrong? Is there is a better way to draw this altogether?
回答1:
You need two bitmaps, one for the picturebox (img) and one to clear it and draw the rectangle(imgClone).
Private mouse_Down As Point
Private img As Bitmap
Private imgClone As Bitmap
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
img = My.Resources..... 'or you can load the image from file
PictureBox1.Image = img 'with this every time you invalidate it draws img to picturebox
imgClone = CType(PictureBox1.Image.Clone, Bitmap)
End Sub
Private Sub PictureBox1_MouseDown(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
mouse_Down = e.Location
End Sub
Private Sub PictureBox1_MouseMove(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
If e.Button = MouseButtons.Left And e.Location <> mouse_Down Then
DrawRectangle(e.Location)
End If
End Sub
Private Sub DrawRectangle(ByVal pnt As Point)
Dim g As Graphics
g = Graphics.FromImage(img)
g.DrawImage(imgClone, 0, 0) 'we are clearing img with imgClone. imgClone contains the original image without the rectangles
If pnt.X = mouse_Down.X Or pnt.Y = mouse_Down.Y Then
g.DrawLine(Pens.Firebrick, mouse_Down.X, mouse_Down.Y, pnt.X, pnt.Y)
Else
g.DrawRectangle(Pens.Firebrick, Math.Min(mouse_Down.X, pnt.X), Math.Min(mouse_Down.Y, pnt.Y),
Math.Abs(mouse_Down.X - pnt.X), Math.Abs(mouse_Down.Y - pnt.Y))
End If
g.Dispose()
PictureBox1.Invalidate() 'draw img to picturebox
End Sub
If you need to clear the picturebox:
Dim g As Graphics
g = Graphics.FromImage(img)
g.DrawImage(imgClone, 0, 0)
g.Dispose()
PictureBox1.Invalidate()
valter
来源：https://stackoverflow.com/questions/25854754/having-trouble-drawing-simple-rectangle-in-picturebox