Split out shared networking code into net_traits crate

Fixes #4476

components/net_traits/image/base.rs

@@ -0,0 +1,86 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use png;
+use stb_image::image as stb_image2;
+use std::iter::range_step;
+use util::vec::byte_swap;
+
+// FIXME: Images must not be copied every frame. Instead we should atomically
+// reference count them.
+pub type Image = png::Image;
+
+// TODO(pcwalton): Speed up with SIMD, or better yet, find some way to not do this.
+fn byte_swap_and_premultiply(data: &mut [u8]) {
+    let length = data.len();
+    for i in range_step(0, length, 4) {
+        let r = data[i + 2];
+        let g = data[i + 1];
+        let b = data[i + 0];
+        let a = data[i + 3];
+        data[i + 0] = ((r as u32) * (a as u32) / 255) as u8;
+        data[i + 1] = ((g as u32) * (a as u32) / 255) as u8;
+        data[i + 2] = ((b as u32) * (a as u32) / 255) as u8;
+    }
+}
+
+pub fn load_from_memory(buffer: &[u8]) -> Option<Image> {
+    if buffer.len() == 0 {
+        return None;
+    }
+
+    if png::is_png(buffer) {
+        match png::load_png_from_memory(buffer) {
+            Ok(mut png_image) => {
+                match png_image.pixels {
+                    png::PixelsByColorType::RGB8(ref mut data) => byte_swap(data.as_mut_slice()),
+                    png::PixelsByColorType::RGBA8(ref mut data) => {
+                        byte_swap_and_premultiply(data.as_mut_slice())
+                    }
+                    _ => {}
+                }
+                Some(png_image)
+            }
+            Err(_err) => None,
+        }
+    } else {
+        // For non-png images, we use stb_image
+        // Can't remember why we do this. Maybe it's what cairo wants
+        static FORCE_DEPTH: uint = 4;
+
+        match stb_image2::load_from_memory_with_depth(buffer, FORCE_DEPTH, true) {
+            stb_image2::LoadResult::ImageU8(mut image) => {
+                assert!(image.depth == 4);
+                // handle gif separately because the alpha-channel has to be premultiplied
+                if is_gif(buffer) {
+                    byte_swap_and_premultiply(image.data.as_mut_slice());
+                } else {
+                    byte_swap(image.data.as_mut_slice());
+                }
+                Some(png::Image {
+                    width: image.width as u32,
+                    height: image.height as u32,
+                    pixels: png::PixelsByColorType::RGBA8(image.data)
+                })
+            }
+            stb_image2::LoadResult::ImageF32(_image) => {
+                error!("HDR images not implemented");
+                None
+            }
+            stb_image2::LoadResult::Error(e) => {
+                error!("stb_image failed: {}", e);
+                None
+            }
+        }
+    }
+}
+
+fn is_gif(buffer: &[u8]) -> bool {
+    match buffer {
+        [b'G',b'I',b'F',b'8', n, b'a', ..] if n == b'7' || n == b'9' => true,
+        _ => false
+    }
+}
+
+