HOWTO: AngleArc in Windows 3.1, Win32s, and Windows 95

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1
• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows 95
      - Microsoft Win32s version 1.3
  

SUMMARY

In Windows version 3.1, Win32s, and Windows 95, you may want to use the functionality provided by the Win32 API AngleArc(). AngleArc() is only supported on Windows NT.

MORE INFORMATION

The AngleArc() function draws a line segment and an arc. The line segment is drawn from the current position to the beginning of the arc. The arc is drawn along the perimeter of a circle with the given radius and center. The length of the arc is defined by the given start and sweep angles. The starting point of the sweep is determined by measuring counterclockwise from the x-axis of the circle by the number of degrees in the start angle. The ending point is similarly located by measuring counterclockwise from the starting point by the number of degrees in the sweep angle.

The code below provides two possible ways of getting functionality similar to that of the AngleArc() function. While both of these methods will work on any Windows platform, the second (AngleArc2) will be substantially faster due to the fact that it uses the Arc() function to draw the sweep rather than calculating each of the segments on the perimeter of the arc.

NOTE: One limitation of the second method is that if the sweep angle is greater than 360 degrees, the arc will not be swept multiple times. In most cases this will not be a problem but in certain cases (constructing paths, for example) this can be a problem.

Sample Code #1

   BOOL AngleArc1(HDC hdc, int X, int Y, DWORD dwRadius,
                  float fStartDegrees, float fSweepDegrees)
   {
     float fCurrentAngle;         // Current angle in radians
     float fStepAngle = 0.03f;  // 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 * 3.141592f;

     /* 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 */
     LineTo(hdc, ix, iy);

     /* 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);
     }

     return TRUE;
   }

Sample Code 2

   BOOL AngleArc2(HDC hdc, int X, int Y, DWORD dwRadius,
                  float fStartDegrees, float fSweepDegrees)
   {
     int iXStart, iYStart;  // End point of starting radial line.
     int iXEnd, iYEnd;       // End point of ending radial line.
     float fStartRadians;   // Start angle in radians.
     float fEndRadians;     // End angle in radians.
     BOOL bResult;            // Function result.
     float fTwoPi = 2.0f * 3.141592f;
   
     /* 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 a point on the starting radial line via */
     /* polar -> cartesian conversion. */
     iXStart = X + (int)((float)dwRadius * (float)cos(fStartRadians));
     iYStart = Y - (int)((float)dwRadius * (float)sin(fStartRadians));
   
     /* Calculate a point on the ending radial line via */
     /* polar -> cartesian conversion. */
     iXEnd = X + (int)((float)dwRadius * (float)cos(fEndRadians));
     iYEnd = Y - (int)((float)dwRadius * (float)sin(fEndRadians));
   
     /* Draw a line to the starting point. */
     if (fSweepDegrees > 0.0f)
      LineTo(hdc, iXStart, iYStart);
     else
      LineTo(hdc, iXEnd, iYEnd);
   
     /* Draw the arc. */
     bResult = Arc(hdc, X - dwRadius, Y - dwRadius,
                        X + dwRadius, Y + dwRadius,
                        iXStart, iYStart,
                        iXEnd, iYEnd);
   
     /* Move to the ending point. Arc() will not do this and ArcTo() */
     /* will not work on Win32s or Win16. */
     if (fSweepDegrees < 0.0f)
      MoveToEx(hdc, iXStart, iYStart, NULL);
     else
      MoveToEx(hdc, iXEnd, iYEnd, NULL);
   
     return bResult;
   }

Keywords          : GdiMisc kbcode
Platform          : Win95 WINDOWS
Issue type        : kbhowto