Expose encoder_for_format() publicly

src/images/dynimage.rs

@@ -11,7 +11,7 @@ use crate::images::buffer::{
     Rgb16Image, Rgb32FImage, RgbImage, Rgba16Image, Rgba32FImage, RgbaImage,
 };
 use crate::io::encoder::ImageEncoderBoxed;
-use crate::io::free_functions::{self, encoder_for_format};
+use crate::io::free_functions;
 use crate::math::resize_dimensions;
 use crate::metadata::Orientation;
 use crate::traits::Pixel;
@@ -1069,7 +1069,7 @@ impl DynamicImage {
     /// convert the image to some color type supported by the encoder. This may result in a loss of
     /// precision or the removal of the alpha channel.
     pub fn write_to<W: Write + Seek>(&self, mut w: W, format: ImageFormat) -> ImageResult<()> {
-        let encoder = encoder_for_format(format, &mut w)?;
+        let encoder = format.encoder(&mut w)?;
         self.write_with_encoder_impl(encoder)
     }
 
@@ -1111,7 +1111,7 @@ impl DynamicImage {
         Q: AsRef<Path>,
     {
         let file = &mut BufWriter::new(File::create(path)?);
-        let encoder = encoder_for_format(format, file)?;
+        let encoder = format.encoder(file)?;
         self.write_with_encoder_impl(encoder)
     }
 }
@@ -1357,7 +1357,7 @@ pub fn write_buffer_with_format<W: Write + Seek>(
     color: impl Into<ExtendedColorType>,
     format: ImageFormat,
 ) -> ImageResult<()> {
-    let encoder = encoder_for_format(format, buffered_writer)?;
+    let encoder = format.encoder(buffered_writer)?;
     encoder.write_image(buf, width, height, color.into())
 }
 

src/io/format.rs

@@ -1,7 +1,9 @@
 use std::ffi::OsStr;
 use std::path::Path;
 
-use crate::error::{ImageError, ImageFormatHint, ImageResult};
+use crate::error::{
+    ImageError, ImageFormatHint, ImageResult, UnsupportedError, UnsupportedErrorKind,
+};
 
 /// An enumeration of supported image formats.
 /// Not all formats support both encoding and decoding.
@@ -375,6 +377,52 @@ impl ImageFormat {
         .iter()
         .copied()
     }
+
+    /// Returns an encoder for this format, or an error if encoding in this format is not supported.
+    pub fn encoder<'a, W: std::io::Write + std::io::Seek>(
+        &self,
+        buffered_write: &'a mut W,
+    ) -> ImageResult<Box<dyn crate::io::encoder::ImageEncoderBoxed + 'a>> {
+        use crate::codecs::*;
+        Ok(match self {
+            #[cfg(feature = "png")]
+            ImageFormat::Png => Box::new(png::PngEncoder::new(buffered_write)),
+            #[cfg(feature = "jpeg")]
+            ImageFormat::Jpeg => Box::new(jpeg::JpegEncoder::new(buffered_write)),
+            #[cfg(feature = "pnm")]
+            ImageFormat::Pnm => Box::new(pnm::PnmEncoder::new(buffered_write)),
+            #[cfg(feature = "gif")]
+            ImageFormat::Gif => Box::new(gif::GifEncoder::new(buffered_write)),
+            #[cfg(feature = "ico")]
+            ImageFormat::Ico => Box::new(ico::IcoEncoder::new(buffered_write)),
+            #[cfg(feature = "bmp")]
+            ImageFormat::Bmp => Box::new(bmp::BmpEncoder::new(buffered_write)),
+            #[cfg(feature = "ff")]
+            ImageFormat::Farbfeld => Box::new(farbfeld::FarbfeldEncoder::new(buffered_write)),
+            #[cfg(feature = "tga")]
+            ImageFormat::Tga => Box::new(tga::TgaEncoder::new(buffered_write)),
+            #[cfg(feature = "exr")]
+            ImageFormat::OpenExr => Box::new(openexr::OpenExrEncoder::new(buffered_write)),
+            #[cfg(feature = "tiff")]
+            ImageFormat::Tiff => Box::new(tiff::TiffEncoder::new(buffered_write)),
+            #[cfg(feature = "avif")]
+            ImageFormat::Avif => Box::new(avif::AvifEncoder::new(buffered_write)),
+            #[cfg(feature = "qoi")]
+            ImageFormat::Qoi => Box::new(qoi::QoiEncoder::new(buffered_write)),
+            #[cfg(feature = "webp")]
+            ImageFormat::WebP => Box::new(webp::WebPEncoder::new_lossless(buffered_write)),
+            #[cfg(feature = "hdr")]
+            ImageFormat::Hdr => Box::new(hdr::HdrEncoder::new(buffered_write)),
+            _ => {
+                return Err(ImageError::Unsupported(
+                    UnsupportedError::from_format_and_kind(
+                        ImageFormatHint::Unknown,
+                        UnsupportedErrorKind::Format(ImageFormatHint::Name(format!("{self:?}"))),
+                    ),
+                ));
+            }
+        })
+    }
 }
 
 #[cfg(test)]

src/io/free_functions.rs

@@ -3,12 +3,11 @@ use std::io::{self, BufRead, BufWriter, Seek, Write};
 use std::path::Path;
 use std::{iter, mem::size_of};
 
-use crate::io::encoder::ImageEncoderBoxed;
-use crate::{codecs::*, ExtendedColorType, ImageReader};
+use crate::{ExtendedColorType, ImageReader};
 
 use crate::error::{
     ImageError, ImageFormatHint, ImageResult, LimitError, LimitErrorKind, ParameterError,
-    ParameterErrorKind, UnsupportedError, UnsupportedErrorKind,
+    ParameterErrorKind,
 };
 use crate::{DynamicImage, ImageDecoder, ImageFormat};
 
@@ -53,54 +52,10 @@ pub fn save_buffer_with_format(
     format: ImageFormat,
 ) -> ImageResult<()> {
     let buffered_file_write = &mut BufWriter::new(File::create(path)?); // always seekable
-    let encoder = encoder_for_format(format, buffered_file_write)?;
+    let encoder = format.encoder(buffered_file_write)?;
     encoder.write_image(buf, width, height, color.into())
 }
 
-pub(crate) fn encoder_for_format<'a, W: Write + Seek>(
-    format: ImageFormat,
-    buffered_write: &'a mut W,
-) -> ImageResult<Box<dyn ImageEncoderBoxed + 'a>> {
-    Ok(match format {
-        #[cfg(feature = "png")]
-        ImageFormat::Png => Box::new(png::PngEncoder::new(buffered_write)),
-        #[cfg(feature = "jpeg")]
-        ImageFormat::Jpeg => Box::new(jpeg::JpegEncoder::new(buffered_write)),
-        #[cfg(feature = "pnm")]
-        ImageFormat::Pnm => Box::new(pnm::PnmEncoder::new(buffered_write)),
-        #[cfg(feature = "gif")]
-        ImageFormat::Gif => Box::new(gif::GifEncoder::new(buffered_write)),
-        #[cfg(feature = "ico")]
-        ImageFormat::Ico => Box::new(ico::IcoEncoder::new(buffered_write)),
-        #[cfg(feature = "bmp")]
-        ImageFormat::Bmp => Box::new(bmp::BmpEncoder::new(buffered_write)),
-        #[cfg(feature = "ff")]
-        ImageFormat::Farbfeld => Box::new(farbfeld::FarbfeldEncoder::new(buffered_write)),
-        #[cfg(feature = "tga")]
-        ImageFormat::Tga => Box::new(tga::TgaEncoder::new(buffered_write)),
-        #[cfg(feature = "exr")]
-        ImageFormat::OpenExr => Box::new(openexr::OpenExrEncoder::new(buffered_write)),
-        #[cfg(feature = "tiff")]
-        ImageFormat::Tiff => Box::new(tiff::TiffEncoder::new(buffered_write)),
-        #[cfg(feature = "avif")]
-        ImageFormat::Avif => Box::new(avif::AvifEncoder::new(buffered_write)),
-        #[cfg(feature = "qoi")]
-        ImageFormat::Qoi => Box::new(qoi::QoiEncoder::new(buffered_write)),
-        #[cfg(feature = "webp")]
-        ImageFormat::WebP => Box::new(webp::WebPEncoder::new_lossless(buffered_write)),
-        #[cfg(feature = "hdr")]
-        ImageFormat::Hdr => Box::new(hdr::HdrEncoder::new(buffered_write)),
-        _ => {
-            return Err(ImageError::Unsupported(
-                UnsupportedError::from_format_and_kind(
-                    ImageFormatHint::Unknown,
-                    UnsupportedErrorKind::Format(ImageFormatHint::Name(format!("{format:?}"))),
-                ),
-            ));
-        }
-    })
-}
-
 static MAGIC_BYTES: [(&[u8], &[u8], ImageFormat); 23] = [
     (b"\x89PNG\r\n\x1a\n", b"", ImageFormat::Png),
     (&[0xff, 0xd8, 0xff], b"", ImageFormat::Jpeg),