Introduce ImageData::get_rect

We use that to send only the pixels that will be actually drawn to the
canvas thread in CanvasRenderingContext2d::PutImageData.

We also make the canvas thread byte swap and premultiply colours in-place.

components/canvas/canvas_data.rs

@@ -13,6 +13,7 @@ use cssparser::RGBA;
 use euclid::{Transform2D, Point2D, Vector2D, Rect, Size2D};
 use ipc_channel::ipc::{IpcBytesSender, IpcSender};
 use num_traits::ToPrimitive;
+use pixels;
 use serde_bytes::ByteBuf;
 use std::mem;
 use std::sync::Arc;
@@ -451,42 +452,22 @@ impl<'a> CanvasData<'a> {
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-putimagedata
     pub fn put_image_data(
         &mut self,
-        imagedata: Vec<u8>,
+        mut imagedata: Vec<u8>,
         offset: Vector2D<i32>,
-        image_data_size: Size2D<i32>,
-        dest_rect: Rect<i32>,
+        imagedata_size: Size2D<i32>,
     ) {
-        assert_eq!(image_data_size.width * image_data_size.height * 4, imagedata.len() as i32);
-
-        let image_size = image_data_size;
-
-        let first_pixel = dest_rect.origin;
-        let mut src_line = (first_pixel.y * (image_size.width * 4) + first_pixel.x * 4) as usize;
-
-        let mut dest =
-            Vec::with_capacity((dest_rect.size.width * dest_rect.size.height * 4) as usize);
-
-        for _ in 0 .. dest_rect.size.height {
-            let mut src_offset = src_line;
-            for _ in 0 .. dest_rect.size.width {
-                let alpha = imagedata[src_offset + 3] as u16;
-                // add 127 before dividing for more accurate rounding
-                let premultiply_channel = |channel: u8| (((channel as u16 * alpha) + 127) / 255) as u8;
-                dest.push(premultiply_channel(imagedata[src_offset + 2]));
-                dest.push(premultiply_channel(imagedata[src_offset + 1]));
-                dest.push(premultiply_channel(imagedata[src_offset + 0]));
-                dest.push(imagedata[src_offset + 3]);
-                src_offset += 4;
-            }
-            src_line += (image_size.width * 4) as usize;
-        }
-
+        assert_eq!(imagedata_size.area() * 4, imagedata.len() as i32);
+        pixels::byte_swap_and_premultiply_inplace(&mut imagedata);
         if let Some(source_surface) = self.drawtarget.create_source_surface_from_data(
-                &dest,
-                dest_rect.size,
-                dest_rect.size.width * 4,
+                &imagedata,
+                imagedata_size,
+                imagedata_size.width * 4,
                 SurfaceFormat::B8G8R8A8) {
-            self.drawtarget.copy_surface(source_surface, Rect::from_size(dest_rect.size), offset.to_point());
+            self.drawtarget.copy_surface(
+                source_surface,
+                Rect::from_size(imagedata_size),
+                offset.to_point(),
+            );
         }
     }
 

components/canvas/canvas_paint_thread.rs

@@ -241,18 +241,8 @@ impl<'a> CanvasPaintThread <'a> {
             Canvas2dMsg::GetImageData(dest_rect, canvas_size, chan) => {
                 self.canvas(canvas_id).image_data(dest_rect, canvas_size, chan)
             },
-            Canvas2dMsg::PutImageData(
-                imagedata,
-                offset,
-                image_data_size,
-                dirty_rect,
-            ) => {
-                self.canvas(canvas_id).put_image_data(
-                    imagedata.into(),
-                    offset,
-                    image_data_size,
-                    dirty_rect,
-                )
+            Canvas2dMsg::PutImageData(imagedata, offset, imagedata_size) => {
+                self.canvas(canvas_id).put_image_data(imagedata.into(), offset, imagedata_size)
             },
             Canvas2dMsg::SetShadowOffsetX(value) => {
                 self.canvas(canvas_id).set_shadow_offset_x(value)

components/canvas_traits/canvas.rs

@@ -54,7 +54,7 @@ pub enum Canvas2dMsg {
     IsPointInPath(f64, f64, FillRule, IpcSender<bool>),
     LineTo(Point2D<f32>),
     MoveTo(Point2D<f32>),
-    PutImageData(ByteBuf, Vector2D<i32>, Size2D<i32>, Rect<i32>),
+    PutImageData(ByteBuf, Vector2D<i32>, Size2D<i32>),
     QuadraticCurveTo(Point2D<f32>, Point2D<f32>),
     Rect(Rect<f32>),
     RestoreContext,

components/script/dom/canvasrenderingcontext2d.rs

@@ -1277,19 +1277,14 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
             return;
         }
 
-        // FIXME(nox): There is no need to make a Vec<u8> of all the pixels
-        // if we didn't want to put the entire image.
-        let buffer = imagedata.get_data_array();
+        let dirty_size = Size2D::new(dirty_width, dirty_height);
+        let dirty_rect = Rect::new(Point2D::new(dirty_x, dirty_y), dirty_size);
 
         // Step 7.
         self.send_canvas_2d_msg(Canvas2dMsg::PutImageData(
-            buffer.into(),
+            imagedata.get_rect(dirty_rect.try_cast().unwrap()).into(),
             origin.to_vector(),
-            imagedata_size,
-            Rect::new(
-                Point2D::new(dirty_x, dirty_y),
-                Size2D::new(dirty_width, dirty_height),
-            ),
+            dirty_size,
         ));
         self.mark_as_dirty();
     }

components/script/dom/imagedata.rs

@@ -9,7 +9,7 @@ use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
-use euclid::Size2D;
+use euclid::{Rect, Size2D};
 use js::jsapi::{Heap, JSContext, JSObject};
 use js::rust::Runtime;
 use js::typedarray::{Uint8ClampedArray, CreateWith};
@@ -149,9 +149,40 @@ impl ImageData {
         }
     }
 
+    #[allow(unsafe_code)]
+    pub fn get_rect(&self, rect: Rect<u32>) -> Vec<u8> {
+        unsafe {
+            assert!(!rect.is_empty());
+            assert!(self.rect().contains_rect(&rect));
+            assert!(!self.data.get().is_null());
+            let cx = Runtime::get();
+            assert!(!cx.is_null());
+            typedarray!(in(cx) let array: Uint8ClampedArray = self.data.get());
+            let slice = array.as_ref().unwrap().as_slice();
+            let area = rect.size.area() as usize;
+            let first_column_start = rect.origin.x as usize * 4;
+            let row_length = self.width as usize * 4;
+            let first_row_start = rect.origin.y as usize * row_length;
+            if rect.origin.x == 0 && rect.size.width == self.width || rect.size.height == 1 {
+                let start = first_column_start + first_row_start;
+                // FIXME(nox): This should be a borrow.
+                return slice[start..start + area * 4].into();
+            }
+            let mut data = Vec::with_capacity(area * 4);
+            for row in slice[first_row_start..].chunks(row_length).take(rect.size.height as usize) {
+                data.extend_from_slice(&row[first_column_start..][..rect.size.width as usize * 4]);
+            }
+            data
+        }
+    }
+
     pub fn get_size(&self) -> Size2D<u32> {
         Size2D::new(self.Width(), self.Height())
     }
+
+    pub fn rect(&self) -> Rect<u32> {
+        Rect::from_size(self.get_size())
+    }
 }
 
 impl ImageDataMethods for ImageData {