[PHPプロ!] GDライブラリで棒チャートを作成するチュートリアル

Good PHP Tutorialsにて、PHPとGDライブラリを使って棒チャートを作成する方法が紹介されています。グラフ作成ライブラリを使わず、GDのみで一から棒チャートを作る方法を、細かく分けて説明しています。

　Good PHP Tutorialsにて、PHPとGDライブラリを使って棒チャートを作成する方法が紹介されています。グラフ作成ライブラリを使わず、GDのみで一から棒チャートを作る方法を、細かく分けて説明しています。

　以下のソースコードを7つの項目に分けて細かく解説されています。

1. phpファイルを準備する
2. データの値をセットする
3. キャンバス（グラフの枠）を描画
4. グリッドと、軸のラベルを描画する
5. 棒グラフを描画する
6. チャートのラベルを描画する
7. チャートを出力する

<?php 
//データをセットする
$graphTitle = "Favorite Reptile";  
$xLabel     = "Reptile";  
$yLabel     = "Votes";  
 
$data['Alligator'] = 12; 
$data['Crocodile'] = 15;  
$data['Iguana']    = 17;  
$data['Snake']     = 3;  
$data['Turtle']    = 25;  
$data['Lizard']    = 3;  
$data['Barney']    = 1;  
  
 
//getting the maximum and minimum values for Y 
$newData = $data;  
asort($newData);  
 
//minimum 
$places = strlen(current($newData)); 
$mod    = pow(10, $places-1);  
$min    = $mod - current($newData);  
  
//maximum 
$places = strlen(end($newData)); 
$mod    = pow(10, $places-1); 
$max     = $mod + end($newData);  
   
$yAxis     = array("min"=>$min, "max"=> $max);  
 
//getting the maximum and minimum values for Y 
$newData = $data;  
asort($newData); 
 
//minimum 
$places = strlen(current($newData));
  //string length of first element in array. so strlen(1) = 1;      
$mod    = pow(10, $places-1);
  //raising that number minus 1 to the power of 10. so pow(10, 0) = 1;    
$min    = $mod - current($newData);
  //subtracting that from the minimum. so 1 - 1 = 0; <-your y-axis minimum  
  
//maximum 
$places = strlen(end($newData)); //strlen(25) = 2;  
$mod    = pow(10, $places-1);    //pow(10, 1) = 10;  
$max     = $mod + end($newData); //10 + 25 = 35; <-- your new y-axis maximum 
   
//storing those min and max values into an array  
$yAxis     = array("min"=>$min, "max"=> $max); 
//------------------------------------------------ 
// キャンバス（グラフのシート）を描画する
//------------------------------------------------ 
//setting the image dimensions 
$canvasWidth  = 500;  
$canvasHeight = 300;  
$perimeter    = 50;  
 
//creating the canvas 
$canvas = imagecreatetruecolor($canvasWidth, $canvasHeight);  
 
//allocating the colors 
$white  = imagecolorallocate($canvas, 255, 255, 255);  
$black  = imagecolorallocate($canvas, 0,0,0);  
$yellow = imagecolorallocate($canvas, 248, 255, 190); 
$blue  = imagecolorallocate($canvas, 3,12,94);  
$grey   = imagecolorallocate($canvas, 102, 102, 102);  
$lightGrey = imagecolorallocate($canvas, 216, 216, 216);  
 
//getting the size of the fonts 
$fontwidth  = imagefontwidth(2); 
$fontheight = imagefontheight(2);  
 
//filling the canvas with light grey 
imagefill($canvas, 0,0, $lightGrey);  
 
//------------------------------------------------ 
// グリッドを描画する
//------------------------------------------------ 
//getting the size of the grid 
$gridWidth  = $canvasWidth  - ($perimeter*2);  
$gridHeight = $canvasHeight - ($perimeter*2);  
 
//getting the grid plane coordinates  
$c1 = array("x"=>$perimeter, "y"=>$perimeter); 
$c2 = array("x"=>$gridWidth+$perimeter, "y"=>$perimeter);  
$c3 = array("x"=>$gridWidth+$perimeter, "y"=>$gridHeight+$perimeter);  
$c4 = array("x"=>$perimeter, "y"=>$gridHeight+$perimeter); 
 
 
//------------------------------------------------ 
// 背景を作成する
//------------------------------------------------ 
imagefilledrectangle($canvas, $c1['x'], $c1['y'],
    $c3['x'], $c3['y'], $white);   
 
//finding the size of the grid squares 
$sqW = $gridWidth/count($data);  
$sqH = $gridHeight/$yAxis['max'];  
 
//------------------------------------------------  
//垂直線と軸の値を描画する
//------------------------------------------------ 
$verticalPadding = $sqW/2;  
foreach($data as $assoc=>$value) 
{     
    //drawing the line 
    imageline($canvas, $verticalPadding+$c4['x']+$increment,
        $c4['y'], $verticalPadding+$c1['x']+$increment,
        $c1['y'], $black); 
     
    //axis values 
    $wordWidth = strlen($assoc)*$fontwidth;  
    $xPos = $c4['x']+$increment+$verticalPadding-($wordWidth/2);  
    ImageString($canvas, 2, $xPos, $c4['y'], $assoc, $black); 
     
    $increment += $sqW; 
} 
 
//------------------------------------------------  
//水平線と値を表示する
//------------------------------------------------ 
//resetting the increment back to 0 
$increment = 0;  
 
for($i=$yAxis['min']; $i<$yAxis['max']; $i++) 
{ 
    //main lines 
        //often the y-values can be in the thousands,
        //if this is the case then we don't want to draw every single 
        //line so we need to make sure that a line is
        // only drawn every 50 or 100 units.  
    if($i%$mod==0){ 
        //drawing the line 
        imageline($canvas, $c4['x'], $c4['y']+$increment,
            $c3['x'], $c3['y']+$increment, $black); 
        //axis values 
        $xPos = $c1['x']-($fontwidth*strlen($i))-5;  
        ImageString($canvas, 2, $xPos, $c4['y']+$increment-
            ($fontheight/2), $i, $black); 
    } 
    //tics 
    //these are the smaller lines between the longer, main lines.  
    elseif(($mod/5)>1 && $i%($mod/5)==0) 
    { 
        imageline($canvas, $c4['x'], $c4['y']+$increment,
            $c4['x']+10, $c4['y']+$increment, $grey); 
    } 
    //because these lines begin at the bottom we want to subtract 
    $increment-=$sqH;  
} 
//getting the size of the grid 
$gridWidth  = $canvasWidth  - ($perimeter*2);  
$gridHeight = $canvasHeight - ($perimeter*2);  
//getting the grid plane coordinates  
$c1 = array("x"=>$perimeter, "y"=>$perimeter); 
$c2 = array("x"=>$gridWidth+$perimeter, "y"=>$perimeter);  
$c3 = array("x"=>$gridWidth+$perimeter, "y"=>$gridHeight+$perimeter);  
$c4 = array("x"=>$perimeter, "y"=>$gridHeight+$perimeter);
 
imagefilledrectangle($canvas, $c1['x'], $c1['y'],
    $c3['x'], $c3['y'], $white);  
//finding the size of the grid squares  
$sqW = $gridWidth/count($data);   
$sqH = $gridHeight/$yAxis['max'];  
//------------------------------------------------  
// 垂直線と軸のラベルを描画する
//------------------------------------------------ 
$verticalPadding = $sqW/2;  
foreach($data as $assoc=>$value) 
{     
    //drawing the line 
    imageline($canvas, $verticalPadding+$c4['x']+$increment,
        $c4['y'], $verticalPadding+$c1['x']+$increment,
        $c1['y'], $black); 
    //axis labels 
    $wordWidth = strlen($assoc)*$fontwidth;  
    $xPos = $c4['x']+$increment+$verticalPadding-($wordWidth/2);  
    ImageString($canvas, 2, $xPos, $c4['y'], $assoc, $black); 
    $increment += $sqW; 
} 
 
$verticalPadding = $sqW/2;  
//drawing the line 
imageline($canvas, $verticalPadding+$c4['x']+$increment,
    $c4['y'], $verticalPadding+$c1['x']+$increment,
    $c1['y'], $black);  
//axis labels 
$wordWidth = strlen($assoc)*$fontwidth;
  //getting the width of the word 
$xPos = $c4['x']+$increment+$verticalPadding-($wordWidth/2);
  //dividing that by 2 to center the word 
ImageString($canvas, 2, $xPos, $c4['y'], $assoc, $black);
  //outputting the word on canvas 
 
//------------------------------------------------  
// 水平線と軸のラベルを描画する
//------------------------------------------------ 
//resetting the increment back to 0 
$increment = 0;  
 
for($i=$yAxis['min']; $i<$yAxis['max']; $i++) 
{ 
    //main lines 
        //often the y-values can be in the thousands,
        //if this is the case then we don't want to draw every single 
        //line so we need to make sure that a line is
        //only drawn every 50 or 100 units.  
    if($i%$mod==0){ 
        //drawing the line 
        imageline($canvas, $c4['x'], $c4['y']+$increment,
            $c3['x'], $c3['y']+$increment, $black); 
        //axis values 
        $xPos = $c1['x']-($fontwidth*strlen($i))-5;  
        ImageString($canvas, 2, $xPos, $c4['y']+$increment-
          ($fontheight/2), $i, $black); 
    } 
    //tics 
    //these are the smaller lines between the longer, main lines.  
    elseif(($mod/5)>1 && $i%($mod/5)==0) 
    { 
        imageline($canvas, $c4['x'], $c4['y']+$increment,
            $c4['x']+10, $c4['y']+$increment, $grey); 
    } 
    //because these lines begin at the bottom we want to subtract 
    $increment-=$sqH;  
}  
    //------------------------------------------------ 
    // 棒グラフを作成する
    //------------------------------------------------ 
    $increment = 0;
      //resetting the increment value 
    $barWidth = $sqW*.2;
      //setting a width size for the bars, play with this number 
    foreach($data as $assoc=>$value) 
    { 
        $yPos = $c4['y']-($value*$sqH); 
        $xPos = $c4['x']+$increment+$verticalPadding-($barWidth/2);  
        imagefilledrectangle($canvas, $xPos, $c4['y'],
            $xPos+$barWidth, $yPos, $blue);  
        $increment += $sqW;  
    } 
 
//Graph Title 
ImageString($canvas, 2, ($canvasWidth/2)-
    (strlen($graphTitle)*$fontwidth)/2,
    $c1['y']-($perimeter/2), $graphTitle, $green);  
 
//X-Axis 
ImageString($canvas, 2, ($canvasWidth/2)-(strlen($xLabel)*$fontwidth)/2,
    $c4['y']+($perimeter/2), $xLabel, $green);  
 
//Y-Axis 
ImageStringUp($canvas, 2, $c1['x']-$fontheight*3,
    $canvasHeight/2+(strlen($yLabel)*$fontwidth)/2, $yLabel, $green);  
header("content-type: image/jpg");  
imagejpeg($canvas);  
imagedestroy($canvas);  
?>

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