

Title  Use the PolyPolyline API function to draw lots of lines quickly 
Description  This example shows how to use the PolyPolyline API function to draw lots of lines quickly in Visual Basic 6. 
Keywords  polyline, PolyPolyline, graphics 
Categories  Graphics 


This program makes several spirals that start at the same point. It adds the points for each spiral to a single array of POINTAPIs. It also creates an array called counts that holds the number of points for each spiral. The PolyPolygon API function uses the counts array to decide which points belong to which polyline.


Private Sub Form_Load()
Const PI = 3.14159265
Const NUM_PLINES = 8
Const PTS_PER_PLINE = 30
Const Dtheta = 2 * PI / PTS_PER_PLINE
Dim cx As Single
Dim cy As Single
Dim num_points As Integer
Dim pts() As POINTAPI
Dim num_polylines As Integer
Dim counts() As Long
Dim i As Integer
Dim j As Integer
Dim theta As Single
Dim r As Single
Dim dr As Single
' Note that API drawing functions always work in pixels.
picCanvas.ScaleMode = vbPixels
picCanvas.AutoRedraw = True
dr = picCanvas.ScaleWidth / 2 / PTS_PER_PLINE
cx = picCanvas.ScaleWidth / 2
cy = picCanvas.ScaleHeight / 2
For i = 1 To NUM_PLINES
' Make a spiral.
theta = i * 2 * PI / NUM_PLINES
r = 0
For j = 1 To PTS_PER_PLINE
' Make a point for this polyline.
num_points = num_points + 1
ReDim Preserve pts(1 To num_points)
With pts(num_points)
.X = cx + r * Cos(theta)
.Y = cy + r * Sin(theta)
End With
theta = theta + Dtheta
r = r + dr
Next j
' Store the number of points in this polyline.
num_polylines = num_polylines + 1
ReDim Preserve counts(1 To num_polylines)
counts(num_polylines) = PTS_PER_PLINE
Next i
' Draw the polylines. pts is the array of points.
' counts is an array giving the number of points
' in each polyline. num_polylines is the number
' of entries in the counts array = the number of
' polylines to draw.
PolyPolyline picCanvas.hdc, pts(1), counts(1), _
num_polylines
End Sub





