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(PECL cairo >= 0.1.0)
CairoContext::arc -- cairo_arc — Adds a circular arc
面向对象风格 (method):
$x 
   ,  float $y 
   ,  float $radius 
   ,  float $angle1 
   ,  float $angle2 
    )过程化风格:
$context 
   ,  float $x 
   ,  float $y 
   ,  float $radius 
   ,  float $angle1 
   ,  float $angle2 
   )
   Adds a circular arc of the given radius to the current path.
   The arc is centered at (x, y), begins at
   angle1 and proceeds in the direction of increasing angles to end at
   angle2.
   If angle2 is less than angle1 it will be
   progressively increased by 2*M_PI until it is greater than angle1.
   
   If there is a current point, an initial line segment will be added to the path to connect the
   current point to the beginning of the arc. If this initial line is undesired,
   it can be avoided by calling  CairoContext::newSubPath()  or procedural 
    cairo_new_sub_path()  before calling  CairoContext::arc() 
   or  cairo_arc() .    Angles are measured in radians. An angle of 0.0 is in the direction of the positive X axis
    (in user space). An angle of M_PI/2.0 radians (90 degrees) is in the direction of the positive
    Y axis (in user space). Angles increase in the direction from the positive X axis toward the
    positive Y axis. So with the default transformation matrix, angles increase in a clockwise direction.    (To convert from degrees to radians, use degrees * (M_PI / 180.).)
    This function gives the arc in the direction of increasing angles; see
     CairoContext::arcNegative()  or  cairo_arc_negative() 
    to get the arc in the direction of decreasing angles.    
  
context A valid CairoContext object
x x position
y y position
radius Radius of the arc
angle1 start angle
angle2 end angle
没有返回值。
Example #1 面向对象风格
  <?php
$s  = new  CairoImageSurface ( CairoFormat :: ARGB32 ,  100 ,  100 );
 $c  = new  CairoContext ( $s );
 $c -> setSourceRgb ( 0 ,  0 ,  0 );
 $c -> paint ();
 $c -> setLineWidth ( 1 );
 $c -> setSourceRgb ( 1 ,  1 ,  1 );
for ( $r  =  50 ;  $r  >  0 ;  $r  -=  10 ) {
  $c -> arc ( 50 ,  50 ,  $r ,  0 ,  2  *  M_PI );
  $c -> stroke ();
  $c -> fill ();
}
 $s -> writeToPng ( dirname ( __FILE__ ) .  '/CairoContext__arc.png' );
 ?>   
Example #2 过程化风格
  <?php
$s  =  cairo_image_surface_create ( CAIRO_SURFACE_TYPE_IMAGE ,  100 ,  100 );
 $c  =  cairo_create ( $s );
 cairo_set_source_rgb ( $c ,  0 ,  0 ,  0 );
 cairo_paint ( $c );
 cairo_set_source_rgb ( $c ,  1 ,  1 ,  1 );
 cairo_set_line_width ( $c ,  1 );
for ( $r  =  50 ;  $r  >  0 ;  $r  -=  10 ) {
  cairo_arc ( $c ,  50 ,  50 ,  $r ,  0 ,  2  *  M_PI );
  cairo_stroke ( $c );
  cairo_fill ( $c );
}
 cairo_surface_write_to_png ( $s ,  dirname ( __FILE__ ) .  '/cairo_arc.png' );
 ?>