Drawing a circle with radial lines - vb6

Question

for i = 0 to 23
'' ...
'' create 'line' control
'' ...
line.x1 = (inner_radius*cos(15 * i)) + centerx
line.y1 = (inner_radius*sin(15 * i)) + centery
line.x2 = (outer_radius*cos(15 * i)) + centerx
line.y2 = (outer_radius*sin(15 * i)) + centery
next
I'm using this algorithm to render many line controls to make something like the following:
The result is rather bizarre:
I think this happens due to the rounding of the cos() and sin() functions, so my question is, is there some algorithm I can apply to fix the rounding? Or is there a better way to render such controls, perhaps?
EDIT:
The problem, as pointed by Hrqls was that I was using degrees instead of radians... this is the function that I ended up using:
Sub ProgressAnim(ByVal centerx, _
ByVal centery, _
ByVal outer_radius, _
ByVal inner_radius, _
ByVal step_count, _
ByVal line_width)
Dim pi
Dim degstep
Dim scan
Dim newcontrol As Line
Dim controlid
pi = 4 * Atn(1)
degstep = pi / (step_count / 2)
For scan = 0 To step_count - 1
controlid = "line" & (scan + 1)
Set newcontrol = Me.Controls.Add("vb.line", controlid)
newcontrol.X1 = centerx + (inner_radius * Cos(degstep * scan))
newcontrol.Y1 = centery + (inner_radius * Sin(degstep * scan))
newcontrol.X2 = centerx + (outer_radius * Cos(degstep * scan))
newcontrol.Y2 = centery + (outer_radius * Sin(degstep * scan))
newcontrol.BorderStyle = 1
newcontrol.BorderWidth = line_width
newcontrol.Visible = True
Next
End Sub
Calling it like this
ProgressAnim 150, 250, 16, 9, 18, 1
produces this:
which is much closer to what I expected... sadly, I still don't know how to achieve anti-aliasing, but this will do. (For the moment, at least) :)

Answer 1

Your problem is that you calculate the angles in degrees while VB uses radians for its angles
have a look at the following project :
Option Explicit
Private Sub Form_Click()
DrawWheel
End Sub
Private Sub DrawWheel()
Dim intI As Integer
Dim sngRadius As Single
Dim sngRadiusY As Single
Dim sngCenterX As Single, sngCenterY As Single
Dim sngX1 As Single, sngY1 As Single
Dim sngX2 As Single, sngY2 As Single
Dim sngStep As Single
Dim sngAngle As Single
Dim sngCos As Single, sngSin As Single
'calculate form sizes
sngRadius = (ScaleWidth - 240) / 2
sngRadiusY = (ScaleHeight - 240) / 2
sngCenterX = 120 + sngRadius
sngCenterY = 120 + sngRadiusY
If sngRadiusY < sngRadius Then sngRadius = sngRadiusY
'draw circle
Circle (sngCenterX, sngCenterY), sngRadius
'calculate step between lines
sngStep = Atn(1) / 3
'draw lines
For intI = 0 To 23
'calculate angle for each line
sngAngle = sngStep * intI
'calculate coordinates for each line
sngCos = Cos(sngAngle)
sngSin = Sin(sngAngle)
sngX1 = sngCenterX + sngCos * sngRadius / 10
sngY1 = sngCenterY + sngSin * sngRadius / 10
sngX2 = sngCenterX + sngCos * sngRadius
sngY2 = sngCenterY + sngSin * sngRadius
'draw each lines
Line (sngX1, sngY1)-(sngX2, sngY2)
'print sequence number
Print CStr(intI)
Next intI
End Sub
Click on the form to draw the wheel
Atn(1) is PI/4 ... For 24 lines you need to divide 2*PI by 24 .. thus you need to divide PI by 12 ... which makes you divide Atn(1) by 3

Answer 2

change for i = 0 to 23 to for i = 0 to 21
and (15 * i) with (0.3 * i)
Try that code in form1 with a timer1:
Dim c As Integer, centerx As Integer, centery As Integer, inner_radius As Integer, outer_radius As Integer
Dim x1 As Single, y1 As Single, x2 As Single, y2 As Single
Private Sub Form_Load()
c = 0
centerx = Form1.Width / 2
centery = Form1.Height / 2
inner_radius = 1200
outer_radius = 1
Timer1.Interval = 200
End Sub
Private Sub Timer1_Timer()
x1 = (inner_radius * Cos(0.3 * c)) + centerx
y1 = (inner_radius * Sin(0.3 * c)) + centery
x2 = (outer_radius * Cos(0.3 * c)) + centerx
y2 = (outer_radius * Sin(0.3 * c)) + centery
Line (x1, y1)-(x2, y2), RGB(0, 0, 0)
c = c + 1
If c = 21 Then Timer1.Enabled = False
End Sub
check your numbers in this example to see the drawing behavior.

Answer 3

I would ensure that you keep the greatest accuracy by using proper fractions of 2PI.
Fiddle with the constants until you get roughly what you want:
Option Explicit
Private Sub Form_Load()
Timer.Interval = 50
End Sub
Private Sub Timer_Timer()
DrawRadialLines
End Sub
Private Sub DrawRadialLines()
Const ksngPI As Single = 3.14159!
Const ksngCircle As Single = 2! * ksngPI
Const ksngInnerRadius As Single = 130!
Const ksngOuterRadius As Single = 260!
Const ksngCenterX As Single = 1200!
Const ksngCenterY As Single = 1200!
Const klSegmentCount As Long = 12
Const klLineWidth As Long = 3
Static s_lActiveSegment As Integer ' The "selected" segment.
Dim lSegment As Long
Dim sngRadians As Single
Dim sngX1 As Single
Dim sngY1 As Single
Dim sngX2 As Single
Dim sngY2 As Single
Dim cLineColour As OLE_COLOR
Me.DrawWidth = klLineWidth
' Overdraw previous graphic.
Me.Line (ksngCenterX - ksngOuterRadius - Screen.TwipsPerPixelX * 2, ksngCenterY - ksngOuterRadius - Screen.TwipsPerPixelY * 2)-(ksngCenterX + ksngOuterRadius + Screen.TwipsPerPixelX * 2, ksngCenterY + ksngOuterRadius + Screen.TwipsPerPixelY * 2), Me.BackColor, BF
For lSegment = 0 To klSegmentCount - 1
'
' Work out the coordinates for the line to be draw from the outside circle to the inside circle.
'
sngRadians = (ksngCircle * CSng(lSegment)) / klSegmentCount
sngX1 = (ksngOuterRadius * Cos(sngRadians)) + ksngCenterX
sngY1 = (ksngOuterRadius * Sin(sngRadians)) + ksngCenterY
sngX2 = (ksngInnerRadius * Cos(sngRadians)) + ksngCenterX
sngY2 = (ksngInnerRadius * Sin(sngRadians)) + ksngCenterY
' Work out how many segments away from the "current segment" we are.
' The current segment should be the darkest, and the further away from this segment we are, the lighter the colour should be.
Select Case Abs(Abs(s_lActiveSegment - lSegment) - klSegmentCount \ 2)
Case 0!
cLineColour = RGB(0, 0, 255)
Case 1!
cLineColour = RGB(63, 63, 255)
Case 2!
cLineColour = RGB(117, 117, 255)
Case Else
cLineColour = RGB(181, 181, 255)
End Select
Me.Line (sngX1, sngY1)-(sngX2, sngY2), cLineColour
Next lSegment
' Move the current segment on by one.
s_lActiveSegment = (s_lActiveSegment + 1) Mod klSegmentCount
End Sub