Add resize_image script function

src/gfx/generated_image.cpp

@@ -304,6 +304,19 @@ bool EnlargeImage::operator == (const GeneratedImage& that) const {
                && border_size == that2->border_size;
 }
 
+// ----------------------------------------------------------------------------- : ResizeImage
+
+Image ResizeImage::generate(const Options& opt) const {
+  Image img = image->generate(opt);
+  return resample(img, width, height);
+}
+bool ResizeImage::operator == (const GeneratedImage& that) const {
+  const ResizeImage* that2 = dynamic_cast<const ResizeImage*>(&that);
+  return that2 && *image == *that2->image
+    && width == that2->width
+    && height == that2->height;
+}
+
 // ----------------------------------------------------------------------------- : CropImage
 
 Image CropImage::generate(const Options& opt) const {

src/gfx/generated_image.hpp

@@ -287,6 +287,21 @@ private:
   double border_size;
 };
 
+// ----------------------------------------------------------------------------- : ResizeImage
+
+/// Resize an image by resampling it
+class ResizeImage : public SimpleFilterImage {
+public:
+    inline ResizeImage(const GeneratedImageP& image, int width, int height)
+        : SimpleFilterImage(image), width(max(1, width)), height(max(1, height))
+    {}
+    Image generate(const Options& opt) const override;
+    bool operator == (const GeneratedImage& that) const override;
+private:
+    int width;
+    int height;
+};
+
 // ----------------------------------------------------------------------------- : CropImage
 
 /// Crop an image at a certain point, to a certain size