Use cargo features to conditionally compile codecs.

The default continues to have all codecs activated, but a user can
opt-in to only supporting specific ones, via features, e.g. depending on
`image`, while only supporting JPEG and GIF:

    [dependencies.image]
    version = "0.2"
    default-features = false
    features = ["jpeg", "gif"]

On my computer `cargo build` takes ~95s, while `cargo build --features
jpeg --no-default-features` (only JPEG) takes ~28s.

This patch also updates the travis file to also compile the library with
each feature, to ensure they continue to compile. These codec features
are all independent, so testing each one individually is sufficient.

Closes image-rs#311.

.travis.yml

@@ -7,10 +7,24 @@ os:
 env:
     global:
         - secure: M2MCRtyP5P/Xf2TSqrbz8cs41TQY04mK/5Fi6qgr77OKLNZlDclKiFY8BmQ6f1JhVccoE5gMIFpfPoVUu8wZ0Pe7/X4IyO4vxWawVQfE6f0NYErD9yqiE1KEi/RGKPOQfL5HFUK7ifnXvLwsAMh1ix9XMgaBZfZLQ8KhkxNRXwI=
+    matrix:
+      - FEATURES=''
+      - FEATURES='gif'
+      - FEATURES='jpeg'
+      - FEATURES='png'
+      - FEATURES='ppm'
+      - FEATURES='tga'
+      - FEATURES='tiff'
+      - FEATURES='webp'
 script:
-    - cargo build -v
-    - cargo test -v
-    - cargo doc -v
+    - if [ -z "$FEATURES" ]; then
+        cargo build -v
+        cargo test -v
+        cargo doc -v
+      else
+        cargo build --no-default-features --features "$FEATURES"
+        cargo test --no-default-features --features "$FEATURES"
+      fi
 after_success: |
     [ $TRAVIS_BRANCH = master ] &&
     [ $TRAVIS_PULL_REQUEST = false ] &&

Cargo.toml

@@ -26,3 +26,14 @@ version = "0.1.15"
 
 [dev-dependencies.glob]
 version = "0.2.3"
+
+[features]
+default = ["gif", "jpeg", "png", "ppm", "tga", "tiff", "webp"]
+
+gif = []
+jpeg = []
+png = []
+ppm = []
+tga = []
+tiff = []
+webp = []

src/dynimage.rs

@@ -2,12 +2,19 @@ use std::old_io;
 use std::iter;
 use std::ascii::OwnedAsciiExt;
 
+#[cfg(feature = "ppm")]
 use ppm;
+#[cfg(feature = "gif")]
 use gif;
+#[cfg(feature = "webp")]
 use webp;
+#[cfg(feature = "jpeg")]
 use jpeg;
+#[cfg(feature = "png")]
 use png;
+#[cfg(feature = "tiff")]
 use tiff;
+#[cfg(feature = "tga")]
 use tga;
 
 use color;
@@ -336,27 +343,30 @@ impl DynamicImage {
         let color = self.color();
 
         let r = match format {
+            #[cfg(feature = "png")]
             image::ImageFormat::PNG  => {
                 let mut p = png::PNGEncoder::new(w);
 
                 try!(p.encode(&bytes, width, height, color));
                 Ok(())
             }
-
+            #[cfg(feature = "ppm")]
             image::ImageFormat::PPM  => {
                 let mut p = ppm::PPMEncoder::new(w);
 
                 try!(p.encode(&bytes, width, height, color));
                 Ok(())
             }
 
+            #[cfg(feature = "jpeg")]
             image::ImageFormat::JPEG => {
                 let mut j = jpeg::JPEGEncoder::new(w);
 
                 try!(j.encode(&bytes, width, height, color));
                 Ok(())
             }
 
+            #[cfg(feature = "gif")]
             image::ImageFormat::GIF => {
                 let mut g = gif::GIFEncoder::new(
                     self.to_rgba(), None, gif::ColorMode::Indexed(0xFF)
@@ -536,9 +546,12 @@ pub fn save_buffer(path: &Path, buf: &[u8], width: u32, height: u32, color: colo
                   .map_or("".to_string(), | s | s.to_string().into_ascii_lowercase());
 
     match &*ext {
+        #[cfg(feature = "jpeg")]
         "jpg" |
         "jpeg" => jpeg::JPEGEncoder::new(fout).encode(buf, width, height, color),
+        #[cfg(feature = "png")]
         "png"  => png::PNGEncoder::new(fout).encode(buf, width, height, color),
+        #[cfg(feature = "ppm")]
         "ppm"  => ppm::PPMEncoder::new(fout).encode(buf, width, height, color),
         format => Err(old_io::IoError {
             kind: old_io::InvalidInput,
@@ -554,11 +567,17 @@ pub fn save_buffer(path: &Path, buf: &[u8], width: u32, height: u32, color: colo
 /// Create a new image from a Reader
 pub fn load<R: Reader+Seek>(r: R, format: ImageFormat) -> ImageResult<DynamicImage> {
     match format {
+        #[cfg(feature = "png")]
         image::ImageFormat::PNG  => decoder_to_image(png::PNGDecoder::new(old_io::BufferedReader::new(r))),
+        #[cfg(feature = "gif")]
         image::ImageFormat::GIF  => decoder_to_image(gif::GIFDecoder::new(old_io::BufferedReader::new(r))),
+        #[cfg(feature = "jpeg")]
         image::ImageFormat::JPEG => decoder_to_image(jpeg::JPEGDecoder::new(old_io::BufferedReader::new(r))),
+        #[cfg(feature = "webp")]
         image::ImageFormat::WEBP => decoder_to_image(webp::WebpDecoder::new(old_io::BufferedReader::new(r))),
+        #[cfg(feature = "tiff")]
         image::ImageFormat::TIFF => decoder_to_image(try!(tiff::TIFFDecoder::new(r))),
+        #[cfg(feature = "tga")]
         image::ImageFormat::TGA => decoder_to_image(tga::TGADecoder::new(r)),
         _ => Err(image::ImageError::UnsupportedError(format!("A decoder for {:?} is not available.", format))),
     }

src/imageops/sample.rs

@@ -475,6 +475,7 @@ mod tests {
     use super::{resize, FilterType};
 
     #[bench]
+    #[cfg(feature = "png")]
     fn bench_resize(b: &mut test::Bencher) {
         let img = ::open(&Path::new("./examples/fractal.png")).unwrap();
         b.iter(|| {

src/lib.rs

@@ -109,12 +109,19 @@ pub mod math;
 pub mod imageops;
 
 // Image Codecs
+#[cfg(feature = "webp")]
 pub mod webp;
+#[cfg(feature = "ppm")]
 pub mod ppm;
+#[cfg(feature = "png")]
 pub mod png;
+#[cfg(feature = "jpeg")]
 pub mod jpeg;
+#[cfg(feature = "gif")]
 pub mod gif;
+#[cfg(feature = "tiff")]
 pub mod tiff;
+#[cfg(feature = "tga")]
 pub mod tga;
 
 

tests/tga.rs

@@ -1,4 +1,5 @@
 #![feature(old_io, old_path)]
+#![cfg(feature = "tga")]
 
 extern crate image;