added coreAvailable() method to drivers

src/Intervention/Image/AbstractDriver.php

@@ -35,6 +35,13 @@ abstract class AbstractDriver
      * @return AbstractColor
      */
     abstract public function parseColor($value);
+
+    /**
+     * Checks if core module installation is available
+     *
+     * @return boolean
+     */
+    abstract protected function coreAvailable();
     
     /**
      * Initiates new image from given input

src/Intervention/Image/Gd/Driver.php

@@ -14,6 +14,12 @@ class Driver extends \Intervention\Image\AbstractDriver
      */
 	public function __construct(Source $source = null, Encoder $encoder = null)
 	{
+        if ( ! $this->coreAvailable()) {
+            throw new \Intervention\Image\Exception\NotSupportedException(
+                "GD Library extension not available with this PHP installation."
+            );
+        }
+
         $this->source = $source ? $source : new Source;
 	    $this->encoder = $encoder ? $encoder : new Encoder;
 	}
@@ -50,4 +56,14 @@ class Driver extends \Intervention\Image\AbstractDriver
     {
         return new Color($value);
     }
+
+    /**
+     * Checks if core module installation is available
+     *
+     * @return boolean
+     */
+    protected function coreAvailable()
+    {
+        return (extension_loaded('gd') && function_exists('gd_info'));
+    }
 }

src/Intervention/Image/Imagick/Driver.php

@@ -14,6 +14,12 @@ class Driver extends \Intervention\Image\AbstractDriver
      */
 	public function __construct(Source $source = null, Encoder $encoder = null)
 	{
+        if ( ! $this->coreAvailable()) {
+            throw new \Intervention\Image\Exception\NotSupportedException(
+                "ImageMagick module not available with this PHP installation."
+            );
+        }
+
         $this->source = $source ? $source : new Source;
 	    $this->encoder = $encoder ? $encoder : new Encoder;
 	}
@@ -56,4 +62,14 @@ class Driver extends \Intervention\Image\AbstractDriver
     {
         return new Color($value);
     }
+
+    /**
+     * Checks if core module installation is available
+     *
+     * @return boolean
+     */
+    protected function coreAvailable()
+    {
+        return (extension_loaded('imagick') && class_exists('Imagick'));
+    }
 }