SWFShape::drawArc

(PHP 5 < 5.3.0, PECL ming SVN)

SWFShape::drawArc — Draws an arc of radius r centered at the current location, from angle startAngle to angle endAngle measured clockwise from 12 o'clock

说明

SWFShape::drawArc ( float $r , float $startAngle , float $endAngle ) : void

Warning

本函数还未编写文档，仅有参数列表。

返回值

没有返回值。

参见

SWFShape::drawCircle() - Draws a circle of radius r centered at the current location, in a counter-clockwise fashion

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User Contributed Notes 2 notes

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brad_fisher at gensler dot com ¶

16 years ago


It seems that the ming library up to at least v0.4.2 has some rounding issues with rendering the arc.  This is most evident as the radius of the arc gets smaller (try drawing a circle/arc with radius 1 using ming, better yet, try 0.5).  The following code renders a much more accurate arc at smaller radii.  It also does range checking/normalization on the angles passed in that ming doesn't do.

<?php

function drawArc( $shape, $r, $startAngle, $endAngle  ) {
    // Normalize the angles
    $delta = $endAngle - $startAngle;
    if ( abs($delta) >= 360)
        $delta = 360;
    else if ($delta < 0)
        $delta += 360;
    else if ($delta == 0)
        return;
    $startAngle = fmod($startAngle, 360);

    /* first determine number of segments, 8 at most */
    $nSegs = 1 + (int)round(7 * ($delta / 360));

    /* subangle is half the angle of each segment */
    $subangle = M_PI * $delta / $nSegs / 360;

    $angle = M_PI * $startAngle / 180;

    $x = $r * sin($angle);
    $y = -$r * cos($angle);

    $shape->movePen($x, $y);

    $controlRadius = $r / cos($subangle);

    for ( $i=0; $i<$nSegs; ++$i )
    {
        $angle += $subangle;
        $controlx = $controlRadius * sin($angle);
        $controly = -$controlRadius * cos($angle);
        $angle += $subangle;
        $anchorx = ($r*sin($angle));
        $anchory = (-$r*cos($angle));

        $shape->drawCurve($controlx-$x, $controly-$y,
                           $anchorx-$controlx, $anchory-$controly);

        $x = $anchorx;
        $y = $anchory;
    }
}

// SWFShape->drawCircle has the same issue with accuracy.  It's a simple thing to use the function above to fix this:
function drawCircle( $shape, $r ) {
    drawArc( $shape, $r, 0, 360 );
}

// EXAMPLE USAGE:

//  Set ming defaults
ming_setScale(20);
ming_useswfversion(7);

$movie = new SWFMovie();
$movie->setBackground( 0xff, 0xff, 0xff );
$movie->setRate(31);

$sprite = new SWFSprite();
$shape = new SWFShape();

// Ming circles (in green)
$shape->setLine( 0, 0, 0xff, 0 );
$shape->movePenTo( 50, 50 );
$shape->drawCircle( 5 );
$shape->movePenTo( 50, 50 );
$shape->drawCircle( 3 );
$shape->movePenTo( 50, 50 );
$shape->drawCircle( 1 );
$shape->movePenTo( 50, 50 );
$shape->drawCircle( 0.5 );

// Drawn with drawCircle function below (in black)
$shape->setLine( 0, 0, 0, 0 );
$shape->movePenTo( 50, 50 );
drawCircle( $shape, 5 );
$shape->movePenTo( 50, 50 );
drawCircle( $shape, 3 );
$shape->movePenTo( 50, 50 );
drawCircle( $shape, 1 );
$shape->movePenTo( 50, 50 );
drawCircle( $shape, 0.5 );

$sprite->add($shape);
$sprite->nextFrame();
$d = $movie->add($sprite);
$movie->setDimension( 100, 100 );
$movie->save( "test.swf" );

?>

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visual77 at gmail dot com ¶

16 years ago


After the arc is drawn, the pen does not return to the original coordinate that the arc started on, which is the center of the circle of which the arc is a part. Instead, the pen will remain at the last spot of the arc.

In the case of a full circle, this means the pen will now be at 12 o'clock on the circle after the arc is drawn.

To revert back to the original position after drawing a circle, you can do this...

<?php

$shape = new SWFShape();
$shape->drawArc(5, 0, 360);
$shape->movePen(0, 5);

?>

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