问题
I am trying to see if an imagebox interacts with an e graphics line. my current code:
e.Graphics.DrawLine(SystemPens.ButtonShadow, a, b);
if (pictureBox1.Bounds.IntersectsWith(e.GraphicsLine.Bounds))
{
dead();
}
I am unsure how to do this.
回答1:
To test for intersection of a rectangle and a line you can either use one of the many methods from the Wikipedia article or use a GDI+ trick involving GraphicsPaths and Regions..:
using System.Drawing.Drawing2D;
..
bool Intersects(Point a, Point b, Rectangle r)
{
if (Math.Min(a.X, b.X) > r.Right) return false; // *
if (Math.Max(a.X, b.X) < r.Left) return false; // *
if (Math.Min(a.Y, b.Y) > r.Bottom) return false; // *
if (Math.Max(a.Y, b.Y) < r.Top) return false; // *
if (r.Contains(a)) return true; // **
if (r.Contains(b)) return true; // **
using (GraphicsPath gp = new GraphicsPath())
using (Pen pen = new Pen(Color.Empty, 0.5f))
using (Region reg = new Region(r))
using (Graphics g = CreateGraphics())
{
gp.AddLine(a,b);
gp.Widen(pen); // we need to widen the line path just a little
reg.Intersect(gp);
if (reg.IsEmpty(g)) return false;
}
return true;
}
Here is a small test result:
Since Region.IsEmpty is probably not very fast I have prepended the call with a few trivial tests for better speed. For a discussion of performance issues with Region see here. From this I guess one can conclude that testing with a simple rectangle will in fact still be reasonably fast..
For a truely fast test you may need to implement a real clipping method. This looks nice..
But the GDI+ trick with the region has one big advantage over the analytical methods: I will work with any shapes you can put into a GraphicsPath, including circles, ellipes, polygons, all sorts of combinations and also complex tracing paths. And since the Region supports all set operations, your imagination is the limit..
This allows you to test complex shapes of spaceships or monsters; and with a few extra tricks you can even test rotated shapes.
Note that if you go for testing complex shapes you will want to:
- pass in the
GraphicsPath - use its bounding rectangle (
gp.GetBounds()) for the first four tests (*) - remove the other two tests (**) since the bounding rectangle will not work now; in fact they only work with rectangles; I had to remove them for the following ellipse demo.
Here is the same example, simply replacing the rectangle with an ellipse:
回答2:
Here you go. The original code was in C and i translated to vb.net. The code works with a line and a rectangle.
'//min_clip_x is the distance of the left side of rect
'//min_clip_y is the distance of the upper side of rect
'//max_clip_x is the distance of the right side of rect
'//min_clip_y is the distance of the down side of rect
Private Function Clip_Line(ByVal x1 As Integer, ByVal y1 As Integer, ByVal x2 As Integer, ByVal y2 As Integer,
ByVal min_clip_x As Integer, ByVal max_clip_x As Integer, ByVal min_clip_y As Integer,
ByVal max_clip_y As Integer) As Boolean
Const CLIP_CODE_C As Integer = 0
Const CLIP_CODE_N As Integer = 8
Const CLIP_CODE_S As Integer = 4
Const CLIP_CODE_E As Integer = 2
Const CLIP_CODE_W As Integer = 1
Const CLIP_CODE_NE As Integer = 10
Const CLIP_CODE_SE As Integer = 6
Const CLIP_CODE_NW As Integer = 9
Const CLIP_CODE_SW As Integer = 5
Dim p1_code As Integer = 0
Dim p2_code As Integer = 0
Dim xc1, yc1, xc2, yc2 As Integer
xc1 = x1
yc1 = y1
xc2 = x2
yc2 = y2
'//determine codes for p1 And p2
If y1 < min_clip_y Then
p1_code = p1_code Or CLIP_CODE_N
Else
If y1 > max_clip_y Then
p1_code = p1_code Or CLIP_CODE_S
End If
End If
If (x1 < min_clip_x) Then
p1_code = p1_code Or CLIP_CODE_W
Else
If (x1 > max_clip_x) Then
p1_code = p1_code Or CLIP_CODE_E
End If
End If
If (y2 < min_clip_y) Then
p2_code = p2_code Or CLIP_CODE_N
Else
If (y2 > max_clip_y) Then
p2_code = p2_code Or CLIP_CODE_S
End If
End If
If (x2 < min_clip_x) Then
p2_code = p2_code Or CLIP_CODE_W
Else
If (x2 > max_clip_x) Then
p2_code = p2_code Or CLIP_CODE_E
End If
End If
'//try And trivially reject
If CBool(p1_code And p2_code) Then
Return False
End If
'//test for totally visible, if so leave points untouched
If (p1_code = 0 And p2_code = 0) Then
Return True
End If
'//determine end clip point for p1
Select Case p1_code
Case CLIP_CODE_C
Exit Select
Case CLIP_CODE_N
yc1 = min_clip_y
xc1 = CInt(x1 + 0.5 + (min_clip_y - y1) * (x2 - x1) / (y2 - y1))
Exit Select
Case CLIP_CODE_S
yc1 = max_clip_y
xc1 = CInt(x1 + 0.5 + (max_clip_y - y1) * (x2 - x1) / (y2 - y1))
Exit Select
Case CLIP_CODE_W
xc1 = min_clip_x
yc1 = CInt(y1 + 0.5 + (min_clip_x - x1) * (y2 - y1) / (x2 - x1))
Exit Select
Case CLIP_CODE_E
xc1 = max_clip_x
yc1 = CInt(y1 + 0.5 + (max_clip_x - x1) * (y2 - y1) / (x2 - x1))
Exit Select
Case CLIP_CODE_NE
'//north hline intersection
yc1 = min_clip_y
xc1 = CInt(x1 + 0.5 + (min_clip_y - y1) * (x2 - x1) / (y2 - y1))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc1 < min_clip_x) Or (xc1 > max_clip_x) Then
'//east vline intersection
xc1 = max_clip_x
yc1 = CInt(y1 + 0.5 + (max_clip_x - x1) * (y2 - y1) / (x2 - x1))
End If
Exit Select
Case CLIP_CODE_SE
'//south hline intersection
yc1 = max_clip_y
xc1 = CInt(x1 + 0.5 + (max_clip_y - y1) * (x2 - x1) / (y2 - y1))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc1 < min_clip_x) Or (xc1 > max_clip_x) Then
'//east vline intersection
xc1 = max_clip_x
yc1 = CInt(y1 + 0.5 + (max_clip_x - x1) * (y2 - y1) / (x2 - x1))
End If
Exit Select
Case CLIP_CODE_NW
'//north hline intersection
yc1 = min_clip_y
xc1 = CInt(x1 + 0.5 + (min_clip_y - y1) * (x2 - x1) / (y2 - y1))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc1 < min_clip_x) Or (xc1 > max_clip_x) Then
xc1 = min_clip_x
yc1 = CInt(y1 + 0.5 + (min_clip_x - x1) * (y2 - y1) / (x2 - x1))
End If
Exit Select
Case CLIP_CODE_SW
'//south hline intersection
yc1 = max_clip_y
xc1 = CInt(x1 + 0.5 + (max_clip_y - y1) * (x2 - x1) / (y2 - y1))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc1 < min_clip_x) Or (xc1 > max_clip_x) Then
xc1 = min_clip_x
yc1 = CInt(CDbl(y1) + 0.5 + CDbl(min_clip_x - x1) * CDbl(y2 - y1) / CDbl(x2 - x1))
End If
Exit Select
Case Else
Exit Select
End Select
'//determine end clip point for p2
Select Case p2_code
Case CLIP_CODE_C
Exit Select
Case CLIP_CODE_N
yc2 = min_clip_y
xc2 = CInt(x2 + (min_clip_y - y2) * (x1 - x2) / (y1 - y2))
Exit Select
Case CLIP_CODE_S
yc2 = max_clip_y
xc2 = CInt(x2 + (max_clip_y - y2) * (x1 - x2) / (y1 - y2))
Exit Select
Case CLIP_CODE_W
xc2 = min_clip_x
yc2 = CInt(y2 + (min_clip_x - x2) * (y1 - y2) / (x1 - x2))
Exit Select
Case CLIP_CODE_E
xc2 = max_clip_x
yc2 = CInt(y2 + (max_clip_x - x2) * (y1 - y2) / (x1 - x2))
Exit Select
Case CLIP_CODE_NE
'//north hline intersection
yc2 = min_clip_y
xc2 = CInt(x2 + 0.5 + (min_clip_y - y2) * (x1 - x2) / (y1 - y2))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc2 < min_clip_x) Or (xc2 > max_clip_x) Then
'//east vline intersection
xc2 = max_clip_x
yc2 = CInt(y2 + 0.5 + (max_clip_x - x2) * (y1 - y2) / (x1 - x2))
End If
Exit Select
Case CLIP_CODE_SE
'//south hline intersection
yc2 = max_clip_y
xc2 = CInt(x2 + 0.5 + (max_clip_y - y2) * (x1 - x2) / (y1 - y2))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc2 < min_clip_x) Or (xc2 > max_clip_x) Then
'//east vline intersection
xc2 = max_clip_x
yc2 = CInt(y2 + 0.5 + (max_clip_x - x2) * (y1 - y2) / (x1 - x2))
End If
Exit Select
Case CLIP_CODE_NW
'//north hline intersection
yc2 = min_clip_y
xc2 = CInt(x2 + 0.5 + (min_clip_y - y2) * (x1 - x2) / (y1 - y2))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc2 < min_clip_x) Or (xc2 > max_clip_x) Then
xc2 = min_clip_x
yc2 = CInt(y2 + 0.5 + (min_clip_x - x2) * (y1 - y2) / (x1 - x2))
End If
Exit Select
Case CLIP_CODE_SW
'//south hline intersection
yc2 = max_clip_y
xc2 = CInt(x2 + 0.5 + (max_clip_y - y2) * (x1 - x2) / (y1 - y2))
'//test if intersection Is valid,
'//if so then done, else compute next
If (xc2 < min_clip_x) Or (xc2 > max_clip_x) Then
xc2 = min_clip_x
yc2 = CInt(y2 + 0.5 + (min_clip_x - x2) * (y1 - y2) / (x1 - x2))
End If
Exit Select
Case Else
Exit Select
End Select
'//do bounds check
If (xc1 < min_clip_x) Or (xc1 > max_clip_x) Or (yc1 < min_clip_y) Or (yc1 > max_clip_y) Or
(xc2 < min_clip_x) Or (xc2 > max_clip_x) Or (yc2 < min_clip_y) Or (yc2 > max_clip_y) Then
Return False '//no collision
End If
Return True '//collision
End Function
来源：https://stackoverflow.com/questions/51217546/test-for-rectangle-line-intersection