PRB: Picture.Circle Works Incorrectly When the Radius is Very Large and the Angle is Very Small (215336)

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.