Add support for PNG decoding (encoding still buggy)

codecs/png/src/lib.rs

@@ -0,0 +1,47 @@
+use std::io::Cursor;
+
+use wasm_bindgen::prelude::*;
+use web_sys::ImageData;
+
+#[wasm_bindgen(catch)]
+pub fn encode(data: &[u8], width: u32, height: u32) -> Vec<u8> {
+    let mut buffer = Cursor::new(Vec::<u8>::new());
+
+    {
+        let mut encoder = png::Encoder::new(&mut buffer, width, height);
+        encoder.set_color(png::ColorType::RGBA);
+        encoder.set_depth(png::BitDepth::Eight);
+        let mut writer = encoder.write_header().unwrap();
+        writer.write_image_data(data).unwrap();
+    }
+
+    buffer.into_inner()
+}
+
+#[wasm_bindgen(catch)]
+pub fn decode(data: &[u8]) -> ImageData {
+    let mut decoder = png::Decoder::new(Cursor::new(data));
+    decoder.set_transformations(png::Transformations::EXPAND);
+    let (info, mut reader) = decoder.read_info().unwrap();
+    let num_pixels = (info.width * info.height) as usize;
+    let mut buf = vec![0; num_pixels * 4];
+    reader.next_frame(&mut buf).unwrap();
+
+    // Transformations::EXPAND will make sure color_type is either
+    // RGBA or RGB. If it’s RGB, we need inject an alpha channel.
+    if info.color_type == png::ColorType::RGB {
+        for i in (0..num_pixels).rev() {
+            buf[i * 4 + 0] = buf[i * 3 + 0];
+            buf[i * 4 + 1] = buf[i * 3 + 1];
+            buf[i * 4 + 2] = buf[i * 3 + 2];
+            buf[i * 4 + 3] = 255;
+        }
+    }
+
+    ImageData::new_with_u8_clamped_array_and_sh(
+        wasm_bindgen::Clamped(&mut buf),
+        info.width,
+        info.height,
+    )
+    .unwrap()
+}