Add GetScrollOffset function to PPB_View

ppapi/api/ppb_view.idl

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /**
  * This file defines the <code>PPB_View</code> struct representing the state
  * of the view of an instance.
  */
 
 [generate_thunk]
 
 label Chrome {
   M18 = 1.0,
-  M28 = 1.1
+  M28 = 1.1,
+  M37 = 1.2

[dmichael (off chromium), 2014/06/11 20:24:14]

It might be best to use channel=dev to start out, while you experiment with it?

[raymes, 2014/06/12 01:06:15]

Done.

 };
 
 /**
  * <code>PPB_View</code> represents the state of the view of an instance.
  * You will receive new view information using
  * <code>PPP_Instance.DidChangeView</code>.
  */
 [macro="PPB_VIEW_INTERFACE"]
 interface PPB_View {
   /**
@@ skipping 55 matching lines @@
    * would not be visible to the user, but IsVisible() will return true.
    *
    * Use the result to speed up or stop updates for invisible module
    * instances.
    *
    * This function performs the duties of GetRect() (determining whether the
    * module instance is scrolled into view and the clip rectangle is nonempty)
    * and IsPageVisible() (whether the page is visible to the user).
    *
    * @param resource A <code>PP_Resource</code> corresponding to a
-   * <code>PPB_View</code> resource. 
+   * <code>PPB_View</code> resource.
    *
    * @return <code>PP_TRUE</code> if the instance might be visible to the
    * user, <code>PP_FALSE</code> if it is definitely not visible.
    */
   PP_Bool IsVisible([in] PP_Resource resource);
 
   /**
    * IsPageVisible() determines if the page that contains the module instance
    * is visible. The most common cause of invisible pages is that
    * the page is in a background tab in the browser.
    *
    * Most applications should use IsVisible() instead of this function since
    * the module instance could be scrolled off of a visible page, and this
    * function will still return true. However, depending on how your module
    * interacts with the page, there may be certain updates that you may want to
    * perform when the page is visible even if your specific module instance is
    * not visible.
    *
    * @param resource A <code>PP_Resource</code> corresponding to a
-   * <code>PPB_View</code> resource. 
+   * <code>PPB_View</code> resource.
    *
    * @return <code>PP_TRUE</code> if the instance is plausibly visible to the
    * user, <code>PP_FALSE</code> if it is definitely not visible.
    */
   PP_Bool IsPageVisible([in] PP_Resource resource);
 
   /**
    * GetClipRect() returns the clip rectangle relative to the upper-left corner
    * of the module instance. This rectangle indicates the portions of the module
    * instance that are scrolled into view.
@@ skipping 22 matching lines @@
    * it is likely that the previous backing store of the module instance will
    * be used for the first paint, and will be updated later when your
    * application generates new content with the new clip. This may cause
    * flickering at the boundaries when scrolling. If you do choose to do
    * partial updates, you may want to think about what color the invisible
    * portions of your backing store contain (be it transparent or some
    * background color) or to paint a certain region outside the clip to reduce
    * the visual distraction when this happens.
    *
    * @param resource A <code>PP_Resource</code> corresponding to a
-   * <code>PPB_View</code> resource. 
+   * <code>PPB_View</code> resource.
    *
    * @param clip Output argument receiving the clip rect on success.
    *
    * @return Returns <code>PP_TRUE</code> if the resource was valid and the
    * clip rect was filled in, <code>PP_FALSE</code> if not.
    */
   PP_Bool GetClipRect([in] PP_Resource resource,
                       [out] PP_Rect clip);
 
   /**
@@ skipping 21 matching lines @@
    * pixel coordinates used for Web content.
    *
    * @param[in] resource A <code>PP_Resource</code> corresponding to a
    * <code>PPB_View</code> resource.
    *
    * @return css_scale A <code>float</code> value representing the number of
    * DIPs per CSS pixel. If the resource is invalid, the value will be 0.0.
    */
   [version=1.1]
   float_t GetCSSScale([in] PP_Resource resource);
+
+  /**
+   * GetScrollOffset returns the scroll offset of the window containing the
+   * plugin. This value will only be valid if the module instance is visible

[dmichael (off chromium), 2014/06/11 20:24:14]

Can you get the same information from the position you get from GetRect combined
with the visible part from GetClipRect?

E.g.:
PP_Rect rect = {};
view->GetRect(view_resource, &rect);
PP_Rect clip_rect = {};
view->GetClipRect(view_resource, &clip_rect);
PP_Point scroll_offset = {rect.point.x + clip_rect.point.x,
                          rect.point.y + clip_rect.point.y};
^^^ Would that you give you the same information? Or am I missing something?

[raymes, 2014/06/12 01:06:15]

I think this works except for the cases where the plugin instance is position:
fixed (as in pdf) and it doesn't move with the rest of the window contents :(

[dmichael (off chromium), 2014/06/16 22:31:55]

Oh, you're using position:fixed? I had thought you were doing something else,
where you tell Graphics2D which part of the plugin's drawing area your ImageData
applies to. That way you'd be able to render more than is displayed to make it
possible for a small scroll to happen without roundtripping to the plugin.

Did you move away from that strategy? Does this mean you have to roundtrip to
the plugin for any scroll?

[raymes, 2014/06/17 00:43:00]

Yeah...unfortunately I put that strategy to the side for now. The problem is
that the compositor support really isn't there yet. If you scroll too quickly
with that approach then we get flickering/checkerboarding because there is no
way at the moment for the compositor to wait for the plugin to deliver a frame.

The requestAnimationFrame pepper API (that Brian and Peng proposed) would make
it possible to go back down this route and get really nice scrolling in PDF, but
for now I've gone with a similar approach to what exists with in-process... :(

+   * (that is, IsVisible() is true) otherwise (0, 0) will be returned.
+   *
+   * @param[in] resource A <code>PP_Resource</code> corresponding to a
+   * <code>PPB_View</code> resource.
+   *
+   * @param[out] offset A <code>PP_Point</code> which will be set to the value
+   * of the scroll offset.

[dmichael (off chromium), 2014/06/11 20:24:14]

in CSS pixels?

[raymes, 2014/06/12 01:06:15]

Done.

+   *
+   * @return Returns <code>PP_TRUE</code> if the resource was valid and the
+   * offset was filled in, <code>PP_FALSE</code> if not.
+   */
+  [version=1.2]
+  PP_Bool GetScrollOffset([in] PP_Resource resource,
+                          [out] PP_Point offset);
 };