imagearc()

(PHP 4, PHP 5, PHP 7)

画椭圆弧

说明

imagearc() 以$cx，$cy（图像左上角为 0, 0）为中心在$image所代表的图像中画一个椭圆弧。$w和$h分别指定了椭圆的宽度和高度，起始和结束点以$s和$e参数以角度指定。0°位于三点钟位置，以顺时针方向绘画。

用 imagearc() 画一个圆

参见 imageellipse()，imagefilledellipse() 和 imagefilledarc()。

This is an example script I wrote for myself to help me learn how to used the imagearc functions. Maybe if will also help others. 

The imagearc function has a precision of one degree. The function truncates the $start and $end values to the inferior degree.
For example if the starting angle you calculated is : -178.62450462172°
and the ending angle is : -152.78056427917°
imagearc will draw a curve from -178° to -152°.
If you need accurate curves drawing, you need to use a loop to draw little step-by-step lines. By creating a large number of short enough lines, you will create the impression of a curve with accuracy.

A previous for the Rotated (Filled)Ellipse note from(nojer2 at yahoo dot com, 02-Apr-2001 12:06) has a mistake, at the second arc. Replace them with the following listing.
if ($filled) {
  triangle($im, $cx, $cy, $cx+$px, $cy+$py, $cx+$x, $cy+$y, $colour);
  triangle($im, $cx, $cy, $cx-$px, $cy-$py, $cx-$x, $cy-$y, $colour);
} else {
  imageline($im, $cx+$px, $cy+$py, $cx+$x, $cy+$y, $colour);
  imageline($im, $cx-$px, $cy-$py, $cx-$x, $cy-$y, $colour);
}

Please note that in order to draw a complete circle or ellipse (without using the imageellipse) you mustn't use 0 for both s and e. If you do this you will get, umm, nothing. Instead set s to 0 and e to 360 to get a complete circle or ellipse.

I needed an arc with a thick border and i didn't like to use 359.9 as end angle so i made a function that works pretty well: 

Right...
possibly the easiest way of drawing a filled circle:
Loop through the imagearc function incrementing the diameter by one pixel:

This works great for circles with diameters up to about 60 or 70 pixels wide. After that, you start to get pixle gaps.

imagesetstyle() sets the style to be used by all line drawing functions when drawing with the special color .
Here goes a example of drawing a dashed-line circle.enjoy! 

Round cornered anti-aliased dynamically sized button.
$w=40;
$h=20;
$im = ImageCreate($w,$h);
$white=ImageColorAllocate($im,255,255,255);
ImageFilledRectangle($im,0,0,$w,$h,$white);
imagecolortransparent ($im, $white);
ImageTTFText ($im, $h+ceil($h/3)+1, 0, -1, $h-1, $col1, "arialbd.ttf", "O");
ImageTTFText ($im, $h+ceil($h/3)+1, 0, $w-$h, $h-1, $col1, "arialbd.ttf", "O");
ImageTTFText ($im, $h+ceil($h/3)+1, 0, 1, $h-1, $col1, "arialbd.ttf", "O");
ImageTTFText ($im, $h+ceil($h/3)+1, 0, $w-$h-2, $h-1, $col1, "arialbd.ttf", "O");
$points=array(
  1,round($h/2), 
  round($h/4),$h-round($h/4), 
  round($h/2),$h, 
  $w-(round($h/2)),$h, 
  $w-(round($h/4)),$h-round($h/4), 
  $w-2,round($h/2), 
  $w-round($h/4),round($h/4), 
  $w-round($h/2),0, 
  round($h/2),0, 
  round($h/4),round($h/4)
);
imagefilledpolygon ($im, $points, 10, $col1);
header("content-type: image/gif");
header("Content-Disposition: filename=name.gif");
ImageGif($im);
ImageDestroy($im);

imagearc example works not well,as it lacks of this line
"$white = imagecolorallocate($img, 255, 255, 255);
  imagefill($img,0,0,$white);
  $black = imagecolorallocate($img, 0, 0, 0);
"

I didn't have much luck with the other two functions, one of them makes circles that look like they've been printed on a dot-matrix printer. This simple function builds a border out of circles, seems to work nicely. 

[note-Apache/1.3.29 (Win32) PHP/4.3.4]
The imagearc (and imageellipse) functions do not accept line thicknesses when drawn from 0 to 360 degrees.
Drawing from 0 to 359 and again from 359 to 360 does create an ellipse with the current line thickness.
Jerry

To fill an arc (DiameterX != DiameterY):

To close the arc with 2 lines (DiameterX != DiameterY):

An example: 

Here's a dashed circle function: 

Here's the function to draw rotated ellipses again. This time I've optimised it a bit, fixed the no-fill bug, and used a 'squishratio' rather than a 'radiusmodifier', to make the curves perfect, so ignore my previous version. 

The wierd thing is that the first two integers tell where to place the "circle".
So for example I first create the "pallet" to place the circle on.
$image = imagecreate(500, 500); 
(this makes a huge 500x500 gif :) )
$colorBody = imagecolorallocate($image, 0, 0, 0);
(make the default color of the "pallet" black
$circleColor = imagecolorallocate($image, 255, 0, 255);
(going to make the circle an ugly pink color)
imagearc($image, 250, 250, 300, 300, 0, 360, $circleColor);
Places the image in the center (250,250) and the circle is 300 pixels in diameter.
Hope this helps.
 
Travis Kent Beste

I wrote a simple function that can draws an arc counter-clockwisekly. Here it is :

The params of this function is exactly the same as the usual imagearc function.

Heres a function to make a curve between two points... This will be a downward curve but it wouldn't be hard to make a similar function to make an upward curve. The first point has to be to the left of the second point ($x1 
To do filled arcs, try something like this:

...well you get the point. It's a kludge, and *very* slow, but it's free.
There is another way to fill an arc : 
I found a better way for drawing a pie chart:
header ("Content-type: image/png");
$diameter = 100;
$radius = $diameter / 2;
$centerX = $radius;
$centerY = $radius;
$im = @ImageCreate ($diameter, $diameter)
  or die ("Cannot Initialize new GD image stream");
$background = ImageColorAllocate ($im, 0, 0, 0);
$red = ImageColorAllocate ($im, 176, 0, 0);
function fill_arc($start, $end, $color) {
  global $diameter, $centerX, $centerY, $im, $radius;
  imagearc($im, $centerX, $centerY, $diameter, $diameter, $start, $end, $color); 
  imageline($im, $centerX, $centerY, $centerX + cos(deg2rad($start)) * $radius, $centerY + sin(deg2rad($start)) * $radius, $color);
  imageline($im, $centerX, $centerY, $centerX + cos(deg2rad($end)) * $radius, $centerY + sin(deg2rad($end)) * $radius, $color);
  imagefill ($im,$centerX + $radius * 0.5 *cos(deg2rad($start+($end-$start)/2)), $centerY + $radius * 0.5 * sin(deg2rad($start+($end-$start)/2)), $color);
  }
fill_arc(0,30,$red);
// Will make a red filled arc, starting at 0 degrees, ending at 30 degrees
ImagePng ($im);
 

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