Make HTMLCanvasElement::fetch_all_data return a shared memory blob

3 files changed, 13 insertions, 10 deletions

diff --git a/components/script/dom/canvasrenderingcontext2d.rs b/components/script/dom/canvasrenderingcontext2d.rs
index 4840966dfb4..a50cce88870 100644
--- a/components/script/dom/canvasrenderingcontext2d.rs
+++ b/components/script/dom/canvasrenderingcontext2d.rs
@@ -1296,7 +1296,11 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
                     .ok_or(Error::InvalidState)?
             },
             CanvasImageSource::HTMLCanvasElement(ref canvas) => {
-                canvas.fetch_all_data().ok_or(Error::InvalidState)?
+                let (data, size) = canvas.fetch_all_data().ok_or(Error::InvalidState)?;
+                let data = data
+                    .map(|data| data.to_vec())
+                    .unwrap_or_else(|| vec![0; size.area() as usize * 4]);
+                (data, size)
             },
             CanvasImageSource::CSSStyleValue(ref value) => value
                 .get_url(self.base_url.clone())
diff --git a/components/script/dom/htmlcanvaselement.rs b/components/script/dom/htmlcanvaselement.rs
index 850f15bdc9e..1dbb0806728 100644
--- a/components/script/dom/htmlcanvaselement.rs
+++ b/components/script/dom/htmlcanvaselement.rs
@@ -36,6 +36,7 @@ use euclid::{Rect, Size2D};
 use html5ever::{LocalName, Prefix};
 use image::png::PNGEncoder;
 use image::ColorType;
+use ipc_channel::ipc::IpcSharedMemory;
 use js::error::throw_type_error;
 use js::jsapi::JSContext;
 use js::rust::HandleValue;
@@ -280,7 +281,7 @@ impl HTMLCanvasElement {
         self.Height() != 0 && self.Width() != 0
     }
 
-    pub fn fetch_all_data(&self) -> Option<(Vec<u8>, Size2D<u32>)> {
+    pub fn fetch_all_data(&self) -> Option<(Option<IpcSharedMemory>, Size2D<u32>)> {
         let size = self.get_size();
 
         if size.width == 0 || size.height == 0 {
@@ -297,7 +298,7 @@ impl HTMLCanvasElement {
                 );
                 context.get_ipc_renderer().send(msg).unwrap();
 
-                receiver.recv().unwrap()?.into()
+                Some(receiver.recv().unwrap())
             },
             Some(&CanvasContext::WebGL(_)) => {
                 // TODO: add a method in WebGLRenderingContext to get the pixels.
@@ -307,7 +308,7 @@ impl HTMLCanvasElement {
                 // TODO: add a method in WebGL2RenderingContext to get the pixels.
                 return None;
             },
-            None => vec![0; size.height as usize * size.width as usize * 4],
+            None => None,
         };
 
         Some((data, size))
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index 07ab777e631..c7896b42436 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/components/script/dom/webglrenderingcontext.rs
@@ -569,12 +569,10 @@ impl WebGLRenderingContext {
                     return Err(Error::Security);
                 }
                 if let Some((data, size)) = canvas.fetch_all_data() {
-                    TexPixels::new(
-                        IpcSharedMemory::from_bytes(&data),
-                        size,
-                        PixelFormat::BGRA8,
-                        true,
-                    )
+                    let data = data.unwrap_or_else(|| {
+                        IpcSharedMemory::from_bytes(&vec![0; size.area() as usize * 4])
+                    });
+                    TexPixels::new(data, size, PixelFormat::BGRA8, true)
                 } else {
                     return Ok(None);
                 }