Q215336: PRB: Picture.Circle Works Wrong if Radius Large and Angle Small
Article: Q215336
Product(s): Microsoft Visual Basic for Windows
Version(s): 5.0,6.0
Operating System(s):
Keyword(s): kbAPI kbGDI kbGrpDSUser kbVBp kbVBp500 kbVBp600 kbVC500 kbVC600 kbOSWin95 kbOSWin98 kbG
Last Modified: 28-JAN-2001
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The information in this article applies to:
- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0
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SYMPTOMS
========
The Circle method of the PictureBox works incorrectly while drawing an arc with
a very large radius and a very small angle. On Windows 2000 or Windows NT you
may get a distorted arc. On Windows 95 or Windows Me you may get nothing.
CAUSE
=====
In Visual Basic, the Circle method of the PictureBox calls the Arc API. The
problem occurs because the Arc API works incorrectly when the radius is very
large and the angle is very small.
RESOLUTION
==========
To work around this problem, you need to implement your own Arc function in
Visual Basic or C. Usually the C function provides better performance.
MORE INFORMATION
================
Steps to Reproduce Behavior
---------------------------
1. Create a new Standard EXE project (Project1). Form1 is created by default.
2. Add a PictureBox to Form1 and change its Name to picTest.
3. Add the following code to the code module of Form1:
Option Explicit
Private Const CirConst As Double = 3.14159265358979
Private Const PISTEP As Double = CirConst / 180#
Private Sub Form_Load()
picTest.AutoRedraw = True
picTest.BackColor = vbBlack
picTest.ForeColor = vbWhite
Me.WindowState = 2
End Sub
Private Sub Form_Resize()
Dim retval As Long
Dim x As Integer, y As Integer
Dim r As Long
Dim a1 As Double, a2 As Double
picTest.Move 0, 0
picTest.Height = Me.ScaleHeight * 0.98
picTest.Width = picTest.Height
Const ZZ As Double = 0.15
picTest.Scale (-ZZ, ZZ + ZZ)-(ZZ, 0)
picTest.Cls
picTest.Circle (-10, 0), 10, , 0 * PISTEP , 1 * PISTEP
End Sub
4. Run the application in Windows 2000 or Windows NT and you see a distorted
arc. Run it in Windows 95 or Windows Me and you see nothing.
Steps to Implement Your Own Arc Function in C
---------------------------------------------
1. Start Microsoft Visual C++ and create a new Win32 Dynamic-Link Library
project.
2. Type "MyGDI" in the Project name text box and click OK.
3. In the next dialog box, choose "a simple dll project" and click the Finish
button.
4. Click OK in the next dialog box.
5. In MyGDI.cpp file, add the following code after the line #include "stdafx.h":
#include "math.h"
extern "C" {
BOOL _stdcall MyArc(HDC hdc, int X, int Y, DWORD dwRadius,
float fStartDegrees, float fSweepDegrees);
}
BOOL _stdcall MyArc(HDC hdc, int X, int Y, DWORD dwRadius,
float fStartDegrees, float fSweepDegrees)
{
float fCurrentAngle; // Current angle in radians
float fStepAngle = 0.003f; // The sweep increment value in radians
float fStartRadians; // Start angle in radians
float fEndRadians; // End angle in radians
int ix, iy; // Current point on arc
float fTwoPi = 2.0f * 3.1415926535f;
int iMM;
POINT pt, pt1;
SIZE szVP, szW;
POINT szOrg, szVPOrg;
// save the old mapping mode
GetWindowExtEx(hdc, &szW);
GetWindowOrgEx(hdc, &szOrg);
GetViewportExtEx(hdc, &szVP);
GetViewportOrgEx(hdc, &szVPOrg);
pt.x = X;
pt.y = Y;
LPtoDP(hdc, &pt, 1);
X = pt.x;
Y = pt.y;
// Calculate the new radius
pt.x = dwRadius;
pt.y = 0;
LPtoDP(hdc, &pt, 1);
pt1.x = 0;
pt1.y = 0;
LPtoDP(hdc, &pt1, 1);
pt.x -= pt1.x;
pt.y -= pt1.y;
dwRadius = (DWORD)sqrt(pt.x * pt.x + pt.y * pt.y);
//set the mapping mode to be something that can be used
//to draw arc directly
iMM = SetMapMode(hdc, MM_ANISOTROPIC);
SetViewportExtEx(hdc, 1, 1, NULL);
SetViewportOrgEx(hdc, 0, 0, NULL);
SetWindowExtEx(hdc, 1, 1, NULL);
SetWindowOrgEx(hdc, 0, 0, NULL);
// Get the starting and ending angle in radians
if (fSweepDegrees > 0.0f) {
fStartRadians = ((fStartDegrees / 360.0f) * fTwoPi);
fEndRadians = (((fStartDegrees + fSweepDegrees) / 360.0f) * fTwoPi);
} else {
fStartRadians = (((fStartDegrees + fSweepDegrees) / 360.0f) * fTwoPi);
fEndRadians = ((fStartDegrees / 360.0f) * fTwoPi);
}
// Calculate the starting point for the sweep via
// polar -> cartesian conversion
ix = X + (int)((float)dwRadius * (float)cos(fStartRadians));
iy = Y - (int)((float)dwRadius * (float)sin(fStartRadians));
// Draw a line to the starting point
MoveToEx(hdc, ix, iy, NULL);
// Calculate and draw the sweep
for (fCurrentAngle = fStartRadians;
fCurrentAngle <= fEndRadians;
fCurrentAngle += fStepAngle) {
// Calculate the current point in the sweep via
// polar -> cartesian conversion
ix = X + (int)((float)dwRadius * (float)cos(fCurrentAngle));
iy = Y - (int)((float)dwRadius * (float)sin(fCurrentAngle));
// Draw a line segment to current point
LineTo(hdc, ix, iy);
}
//restore the mapping mode
SetMapMode(hdc, iMM);
SetViewportExtEx(hdc, szVP.cx, szVP.cy, NULL);
SetViewportOrgEx(hdc, szVPOrg.x, szVPOrg.y, NULL);
SetWindowExtEx(hdc, szW.cx, szW.cy, NULL);
SetWindowOrgEx(hdc, szOrg.x, szOrg.y, NULL);
return TRUE;
}
6. Under the File menu, select New. Choose Text File from the list on the Files
tab. Type "MyGDI.def" (without the quotes) in the File Name text box. Click
OK.
7. Add the following code to the MyGDI.def file.
LIBRARY MyGDI
EXPORTS
MyArc @1
8. Build the project and move the MyGDI.dll to the windows system directory or
the same directory as the Visual Basic project.
Steps To Use Your Arc Function in Visual Basic
----------------------------------------------
1. Create a new Standard EXE project. Form1 is created by default.
2. Add a picturebox to Form1. Use the default name, Picture1.
3. Add the following to the code window of Form1:
Option Explicit
Private Type POINTAPI
x As Long
y As Long
End Type
Private Type size
CX As Long
CY As Long
End Type
Private Type rect
Left As Long
Top As Long
Right As Long
Bottom As Long
End Type
Private Declare Function GetStockObject Lib "gdi32" _
(ByVal nIndex As Long) As Long
Private Declare Function SelectObject Lib "gdi32" _
(ByVal hdc As Long, ByVal hObject As Long) As Long
Private Declare Function SetViewportExtEx Lib "gdi32" _
(ByVal hdc As Long, ByVal nX As Long, ByVal nY As Long, _
lpSize As size) As Long
Private Declare Function SetViewportOrgEx Lib "gdi32" _
(ByVal hdc As Long, ByVal nX As Long, ByVal nY As Long, _
lpPoint As POINTAPI) As Long
Private Declare Function SetMapMode Lib "gdi32" _
(ByVal hdc As Long, ByVal nMapMode As Long) As Long
Private Declare Function SetWindowExtEx Lib "gdi32" _
(ByVal hdc As Long, ByVal nX As Long, ByVal nY As Long, _
lpSize As size) As Long
Private Declare Function SetWindowOrgEx Lib "gdi32" _
(ByVal hdc As Long, ByVal nX As Long, ByVal nY As Long, _
lpPoint As POINTAPI) As Long
Private Declare Function GetClientRect Lib "user32" _
(ByVal hwnd As Long, lpRect As rect) As Long
Private Declare Function MyArc Lib "MyGDI" _
(ByVal hdc As Long, ByVal CX As Long, _
ByVal CY As Long, ByVal Radius As Long, _
ByVal sDegree As Single, _
ByVal SweepDegree As Single) As Long
Private Const LOGPIXELSX = 88 ' Logical pixels/inch in X
Private Const LOGPIXELSY = 90 ' Logical pixels/inch in Y
Private Const WHITE_PEN = 6
Private Const BLACK_PEN = 7
Private Const MM_ANISOTROPIC = 8
Private Const CirConst As Double = 3.14159265358979
Private Const PI As Double = CirConst / 180#
Private Sub Form_Load()
Me.WindowState = 2
End Sub
Private Sub Form_Paint()
draw Picture1, False
End Sub
Private Sub draw(picTest As Object, bPrint As Boolean)
Dim retval As Long
Dim x As Integer, y As Integer
Dim R As Long
Dim a1 As Double, a2 As Double
Dim usepen&, oldpen&
Dim size As size
Dim point As POINTAPI
Dim rect As rect
picTest.Move 0, 0
picTest.Height = Me.ScaleHeight * 0.98
picTest.Width = picTest.Height
picTest.Cls
usepen = GetStockObject(BLACK_PEN)
oldpen = SelectObject(picTest.hdc, usepen)
SetMapMode picTest.hdc, MM_ANISOTROPIC
GetClientRect picTest.hwnd, rect
SetViewportExtEx picTest.hdc, _
rect.Right - rect.Left, _
rect.Bottom - rect.Top, size
SetWindowExtEx picTest.hdc, 30, -30, size
SetWindowOrgEx picTest.hdc, -15, 30, point
MyArc picTest.hdc, -1000, 0, 1000, 0, 1
End Sub
4. Run the application and you can see the correct Arc.
Additional query words:
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Keywords : kbAPI kbGDI kbGrpDSUser kbVBp kbVBp500 kbVBp600 kbVC500 kbVC600 kbOSWin95 kbOSWin98 kbGrpDSVB kbOSWinME
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Version : :5.0,6.0
Issue type : kbprb
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