460073 - Add a simple wrapper for rendering HTML content to an image

Status: RESOLVED DUPLICATE of bug 596743

(Core Graveyard :: Embedding: APIs, defect)

Description

[Mark Finkle (:mfinkle) (use needinfo?)]

Since the embedding wrappers use standalone linking, we can't just clone the canvas::drawWindow code into the wrapper layer. The thebes code require dependent linking.

So, I'm going to try to add a method to nsIDOMWindowUtils. The method should return a safe interface, not raw bits. The embedding wrapper layer can pull out the raw bits.

Comment 1

[Mark Finkle (:mfinkle) (use needinfo?)]

Attachment: adds drawWindow to nsIDOMWindowUtils

This patch adds drawWindow to nsIDOMWindowUtils. The method works in a similar way to the canvas version, without any security checks since you must be chrome to access nsIDOMWindowUtils anyway.

The method also requires the caller pass in an image encoder. After the call completes the caller can do what they want with the encoded data.

I'll attach a simple example of a caller next.

Comment 2

[Mark Finkle (:mfinkle) (use needinfo?)]

  ... assume domWindow is an instance of nsIDOMWindow

  nsCOMPtr<nsIDOMWindowUtils> utils = do_GetInterface(domWindow);
  if (utils) {
    nsCOMPtr<imgIEncoder> encoder = do_CreateInstance("@mozilla.org/image/encoder;2?type=image/png");
  
    rv = utils->DrawWindow(0, 0, 1000, 1000, NS_RGB(255, 255, 255), encoder);
    
    nsAutoString fileName(NS_LITERAL_STRING("e:\\dummy-new.png"));
    nsCOMPtr<nsILocalFile> file = do_CreateInstance("@mozilla.org/file/local;1");
    rv = file->InitWithPath(fileName);

    PRUint32 length;
    encoder->Available(&length);

    nsCOMPtr<nsIOutputStream> outputStream;
    rv = NS_NewLocalFileOutputStream(getter_AddRefs(outputStream), file);

    nsCOMPtr<nsIOutputStream> bufferedOutputStream;
    rv = NS_NewBufferedOutputStream(getter_AddRefs(bufferedOutputStream), outputStream, length);

    PRUint32 numWritten;
    rv = bufferedOutputStream->WriteFrom(encoder, length, &numWritten);
  }

Comment 3

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Wouldn't it make more sense to render the window contents into a platform-specific graphics surface, or possibly a raw RGBA pixel buffer? It seems to me that will be wanted far more often than a PNG or other compressed format.

Comment 4

[Mark Finkle (:mfinkle) (use needinfo?)]

> Wouldn't it make more sense to render the window contents into a
> platform-specific graphics surface, or possibly a raw RGBA pixel buffer? It
> seems to me that will be wanted far more often than a PNG or other compressed
> format.

More detail from IRC: roc suggests passing a platform specific structure, like HDC on Windows, would make more sense from an embedding standpoint. We could also request PDF and SVG easier this way. The IDL would change to a: voidPtr and an enum to specify the type of structure.

This means the method is no longer scriptable (yes, attachment 343997 [details] [diff] [review] can be called from JS too). This shouldn't be a big concern.

roc also mentioned the idea of moving this from nsIDOMWindowUtils and creating a component explicitly for embedding.

Comment 5

[Stuart Parmenter]

it makes more sense to me to use thebes here, than try to reinvent platform surfaces.

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

We can't expose Thebes to embedders, or glue code in the embedding layer, since they can't link to the Thebes symbols. (See comment #0.)

Anyway, the simplest possible API for embedders is not Thebes but just to pass in an HDC or whatever. Once we get that HDC across to libxul, sure, the first thing we do is wrap it in a gfxWindowsSurface.

Comment 7

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Comment on attachment 343997 [details] [diff] [review]
adds drawWindow to nsIDOMWindowUtils

I presume this is no longer needed

Comment 8

[Oleg Romashin (:romaxa)]

(In reply to comment #7)
> Comment on attachment 343997 [details] [diff] [review]
> adds drawWindow to nsIDOMWindowUtils
> 
> I presume this is no longer needed

Needed