Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

◄Function Group►  ◄Overview►                          ◄Up► ◄Next► ◄Previous►
────────────────────────────────────────────────────────────────────────────
 
#define INCL_GPIPRIMITIVES
 
LONG GpiPartialArc(hps, pptl, fxMultiplier, fxStartAngle, fxSweepAngle)
HPS hps;               /* presentation-space handle             */
PPOINTL pptl;          /* address of structure for center point */
FIXED fxMultiplier;    /* arc-size multiplier                   */
FIXED fxStartAngle;    /* start angle of arc                    */
FIXED fxSweepAngle;    /* sweep angle of arc                    */
 
The GpiPartialArc function draws a partial arc. The function actually draws
two figures: a straight line, from the current position to the start point
of an arc; and the arc itself, with its center at the specified point. The
function determines the start and end points of the arc by using the start
and sweep angles specified by the fxStartAngle and fxSweepAngle functions.
 
The GpiPartialArc function moves the current position to the end point on
the partial arc.
 
Parameter     Description
────────────────────────────────────────────────────────────────────────────
 
hps           Identifies the presentation space.
 
pptl          Points to a POINTL structure that contains the center point.
 
fxMultiplier  Specifies the amount to scale the width and height of the arc.
              It must be a fixed-point value in the range 1 through 255 (or
              in the range 0x10000 to 0xFF0000 if expressed as a 32-bit
              value). This means the function can scale the arc from 1 to
              255 times the current arc-parameter dimensions.
 
fxStartAngle  Specifies the start angle in degrees. It must be a positive,
              fixed-point value.
 
fxSweepAngle  Specifies the sweep angle in degrees. It must be a positive,
              fixed-point value.
 
Return Value
 
The return value is GPI_OK or GPI_HITS if the function is successful (it is
GPI_HITS if the detectable attribute is set for the presentation space and a
correlation hit occurs). The return value is GPI_ERROR if an error occurs.
 
Errors
 
Use the WinGetLastError function to retrieve the error value, which may be
one of the following:
 
     PMERR_INV_ANGLE_PARM
     PMERR_INV_COORDINATE
     PMERR_INV_HPS
     PMERR_INV_MULTIPLIER
     PMERR_PS_BUSY
 
Comments
 
To draw the arc, the GpiPartialArc function first constructs an imaginary
unit circle at the specified center point. The function locates the start
point of the arc by measuring counterclockwise from the x-axis of the circle
by the number of degrees in the start angle. It then locates the end point
of the arc by measuring counterclockwise from the start point by the number
of degrees in the sweep angle. Finally, the function draws the arc by
applying the current arc parameters and the arc-size multiplier. The
direction in which the function draws the arc depends on the arc parameters.
The direction may affect the way a closed figure containing an arc is
filled.
 
If the sweep angle is greater than 360 degrees, the function draws one or
more complete circles or ellipses (depending on the original sweep-angle
value) followed by an arc. The sweep angle of the final arc is the remainder
after dividing the original sweep angle by 360.
 
Example
 
This example uses the GpiPartialArc function to draw a chord. A chord is an
arc whose end points are connected by a straight line.
 
POINTL ptl = { 100, 100 };             /* center point for arc */
 
GpiSetLineType(hps, LINETYPE_INVISIBLE);
GpiPartialArc(hps, &ptl, MAKEFIXED(50, 0), MAKEFIXED(0, 0),
    MAKEFIXED(180, 0));
GpiSetLineType(hps, LINETYPE_SOLID);
GpiPartialArc(hps, &ptl, MAKEFIXED(50, 0), MAKEFIXED(0, 0),
    MAKEFIXED(180, 0));
 
See Also
 
GpiFullArc, GpiLine, GpiMove, GpiPointArc, GpiQueryArcParams,
GpiSetArcParams, GpiSetAttrs, GpiSetColor, GpiSetCurrentPosition,
GpiSetLineType, WinGetLastError, POINTL
 
                                      ♦