Improve RotateModifier for GD driver

src/Drivers/Gd/Modifiers/RotateModifier.php

@@ -2,34 +2,97 @@
 
 namespace Intervention\Image\Drivers\Gd\Modifiers;
 
+use Intervention\Image\Colors\Rgb\Channels\Blue;
+use Intervention\Image\Colors\Rgb\Channels\Green;
+use Intervention\Image\Colors\Rgb\Channels\Red;
 use Intervention\Image\Drivers\Abstract\Modifiers\AbstractRotateModifier;
 use Intervention\Image\Drivers\Gd\Traits\CanHandleColors;
+use Intervention\Image\Geometry\Rectangle;
+use Intervention\Image\Interfaces\ColorInterface;
+use Intervention\Image\Interfaces\FrameInterface;
 use Intervention\Image\Interfaces\ImageInterface;
 use Intervention\Image\Interfaces\ModifierInterface;
+use Intervention\Image\Traits\CanBuildNewImage;
 
 class RotateModifier extends AbstractRotateModifier implements ModifierInterface
 {
     use CanHandleColors;
+    use CanBuildNewImage;
 
     public function apply(ImageInterface $image): ImageInterface
     {
+        $background = $this->handleInput($this->background);
+
         foreach ($image as $frame) {
-            // retain resolution because imagerotate() seems to reset density to 96dpi
+            $this->modify($frame, $background);
-            $resolution = imageresolution($frame->core());
-
-            // rotate image
-            $frame->setCore(
-                imagerotate(
-                    $frame->core(),
-                    $this->rotationAngle(),
-                    $this->colorToInteger($this->backgroundColor())
-                )
-            );
-
-            // restore original image resolution
-            imageresolution($frame->core(), $resolution[0], $resolution[1]);
         }
 
         return $image;
     }
+
+    protected function modify(FrameInterface $frame, ColorInterface $background): void
+    {
+        // rotate original image against transparent background
+        $rotated = imagerotate(
+            $frame->core(),
+            $this->rotationAngle(),
+            imagecolorallocatealpha(
+                $frame->core(),
+                $background->channel(Red::class)->value(),
+                $background->channel(Green::class)->value(),
+                $background->channel(Blue::class)->value(),
+                127
+            )
+        );
+
+        // create size from original after rotation
+        $container = (new Rectangle(
+            imagesx($rotated),
+            imagesy($rotated),
+        ))->movePivot('center');
+
+        // create size from original and rotate points
+        $cutout = (new Rectangle(
+            imagesx($frame->core()),
+            imagesy($frame->core()),
+            $container->pivot()
+        ))->align('center')
+            ->valign('center')
+            ->rotate($this->rotationAngle() * -1);
+
+        // create new gd image
+        $modified = $this->imageFactory()->newCore(
+            imagesx($rotated),
+            imagesy($rotated),
+            $background
+        );
+
+        // define transparent colors
+        $transparent = imagecolorallocatealpha($modified, 255, 0, 255, 127);
+        imagecolortransparent($modified, $transparent);
+
+        // draw the cutout on new gd image to have a transparent
+        // background where the rotated image will be placed
+        imagealphablending($modified, false);
+        imagefilledpolygon(
+            $modified,
+            $cutout->toArray(),
+            $transparent
+        );
+
+        // place rotated image on new gd image
+        imagealphablending($modified, true);
+        imagecopy(
+            $modified,
+            $rotated,
+            0,
+            0,
+            0,
+            0,
+            imagesx($rotated),
+            imagesy($rotated)
+        );
+
+        $frame->setCore($modified);
+    }
 }