Avoid ctx.getImageData in canvas.toDataURL

2 files changed, 29 insertions, 22 deletions

diff --git a/components/script/dom/canvasrenderingcontext2d.rs b/components/script/dom/canvasrenderingcontext2d.rs
index 5aa1518932d..2617f9e7ed5 100644
--- a/components/script/dom/canvasrenderingcontext2d.rs
+++ b/components/script/dom/canvasrenderingcontext2d.rs
@@ -575,6 +575,28 @@ impl CanvasRenderingContext2D {
     fn set_origin_unclean(&self) {
         self.origin_clean.set(false)
     }
+
+    pub fn get_rect(&self, rect: Rect<u32>) -> Vec<u8> {
+        assert!(self.origin_is_clean());
+
+        // FIXME(nox): This is probably wrong when this is a context for an
+        // offscreen canvas.
+        let canvas_size = self.canvas.as_ref().map_or(Size2D::zero(), |c| c.get_size());
+        assert!(Rect::from_size(canvas_size).contains_rect(&rect));
+
+        let (sender, receiver) = ipc::bytes_channel().unwrap();
+        self.send_canvas_2d_msg(Canvas2dMsg::GetImageData(rect, canvas_size, sender));
+        let mut pixels = receiver.recv().unwrap().to_vec();
+
+        for chunk in pixels.chunks_mut(4) {
+            let b = chunk[0];
+            chunk[0] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + chunk[2] as usize];
+            chunk[1] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + chunk[1] as usize];
+            chunk[2] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + b as usize];
+        }
+
+        pixels
+    }
 }
 
 pub trait LayoutCanvasRenderingContext2DHelpers {
@@ -1154,18 +1176,7 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
             },
         };
 
-        let (sender, receiver) = ipc::bytes_channel().unwrap();
-        self.send_canvas_2d_msg(Canvas2dMsg::GetImageData(read_rect, canvas_size, sender));
-        let mut pixels = receiver.recv().unwrap().to_vec();
-
-        for chunk in pixels.chunks_mut(4) {
-            let b = chunk[0];
-            chunk[0] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + chunk[2] as usize];
-            chunk[1] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + chunk[1] as usize];
-            chunk[2] = UNPREMULTIPLY_TABLE[256 * (chunk[3] as usize) + b as usize];
-        }
-
-        ImageData::new(&self.global(), size.width, size.height, Some(pixels))
+        ImageData::new(&self.global(), size.width, size.height, Some(self.get_rect(read_rect)))
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-putimagedata
diff --git a/components/script/dom/htmlcanvaselement.rs b/components/script/dom/htmlcanvaselement.rs
index 78e74641347..798c4e9d93c 100644
--- a/components/script/dom/htmlcanvaselement.rs
+++ b/components/script/dom/htmlcanvaselement.rs
@@ -7,7 +7,6 @@ use canvas_traits::canvas::{CanvasMsg, CanvasId, FromScriptMsg};
 use canvas_traits::webgl::WebGLVersion;
 use dom::attr::Attr;
 use dom::bindings::cell::DomRefCell;
-use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasRenderingContext2DMethods;
 use dom::bindings::codegen::Bindings::HTMLCanvasElementBinding;
 use dom::bindings::codegen::Bindings::HTMLCanvasElementBinding::{HTMLCanvasElementMethods, RenderingContext};
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLContextAttributes;
@@ -27,7 +26,7 @@ use dom::virtualmethods::VirtualMethods;
 use dom::webgl2renderingcontext::WebGL2RenderingContext;
 use dom::webglrenderingcontext::{LayoutCanvasWebGLRenderingContextHelpers, WebGLRenderingContext};
 use dom_struct::dom_struct;
-use euclid::Size2D;
+use euclid::{Rect, Size2D};
 use html5ever::{LocalName, Prefix};
 use image::ColorType;
 use image::png::PNGEncoder;
@@ -354,10 +353,8 @@ impl HTMLCanvasElementMethods for HTMLCanvasElement {
         _quality: HandleValue,
     ) -> Fallible<USVString> {
         // Step 1.
-        if let Some(CanvasContext::Context2d(ref context)) = *self.context.borrow() {
-            if !context.origin_is_clean() {
-                return Err(Error::Security);
-            }
+        if !self.origin_is_clean() {
+            return Err(Error::Security);
         }
 
         // Step 2.
@@ -366,10 +363,9 @@ impl HTMLCanvasElementMethods for HTMLCanvasElement {
         }
 
         // Step 3.
-        let raw_data = match *self.context.borrow() {
+        let file = match *self.context.borrow() {
             Some(CanvasContext::Context2d(ref context)) => {
-                // FIXME(nox): This shouldn't go through ImageData etc.
-                context.GetImageData(0, 0, self.Width() as i32, self.Height() as i32)?.to_vec()
+                context.get_rect(Rect::from_size(self.get_size()))
             },
             Some(CanvasContext::WebGL(ref context)) => {
                 match context.get_image_data(self.Width(), self.Height()) {
@@ -392,7 +388,7 @@ impl HTMLCanvasElementMethods for HTMLCanvasElement {
         // FIXME: Only handle image/png for now.
         let mut png = Vec::new();
         PNGEncoder::new(&mut png)
-            .encode(&raw_data, self.Width(), self.Height(), ColorType::RGBA(8))
+            .encode(&file, self.Width(), self.Height(), ColorType::RGBA(8))
             .unwrap();
         let mut url = "data:image/png;base64,".to_owned();
         // FIXME(nox): Should this use base64::URL_SAFE?