Implement HiDPI support in Pepper dev interface

ppapi/api/private/ppb_view_private.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 contains the <code>PPB_View_Private</code> interface. */
+label Chrome {
+  M22 = 0.1
+};
+
+/* PPB_View_Private interface */
+interface PPB_View_Private {

[brettw, 2012/06/18 21:17:24]

Do you mind making this a dev interface instead of a private one? Sorry to make
you move/rename the file. But this is the type of thing we want to expose to web
content eventually, rather than something we want to keep internal to the
browser.

[Josh Horwich, 2012/06/19 02:01:04]

Done.

+  /**
+   * GetDeviceScale returns the scale factor between device pixels and DIPs
+   * (also known as logical pixels or UI pixels on some platforms). This allows
+   * the developer to render their contents at device resolution, even as
+   * coordinates / sizes are given in DIPs through the API.
+   *
+   * Note that the coordinate system for Pepper APIs is DIPs. Also note that
+   * one DIP might not equal one CSS pixel - when page scale/zoom is in effect.
+   *
+   * @param[in] resource A <code>PP_Resource</code> corresponding to a
+   * <code>PPB_View</code> resource.
+   *
+   * @param[out] device_scale A <code>float</code> value representing the number
+   * of device pixels per DIP.
+   *
+   * @return Returns <code>PP_TRUE</code> if the resource was valid and the
+   * scale was filled in, <code>PP_FALSE</code> if not.
+   */
+  PP_Bool GetDeviceScale([in] PP_Resource resource,

[brettw, 2012/06/18 21:17:24]

I usually prefer APIs that just return the value when possible. So can this be:
  float GetDeviceScale([in] PP_Resource resource);
and then say that it returns 0 for invalid resources?

[Josh Horwich, 2012/06/19 02:01:04]

Done.

+                         [out] float_t device_scale);
+
+  /**
+   * GetCSSScale returns the scale factor between DIPs and CSS pixels. This
+   * allows proper scaling between DIPs - as sent via the Pepper API - and CSS
+   * pixel coordinates used for Web content.
+   *
+   * @param[in] resource A <code>PP_Resource</code> corresponding to a
+   * <code>PPB_View</code> resource.
+   *
+   * @param[out] css_scale A <code>float</code> value representing the number of
+   * DIPs per CSS pixel.
+   *
+   * @return Returns <code>PP_TRUE</code> if the resource was valid and the
+   * scale was filled in, <code>PP_FALSE</code> if not.
+   */
+  PP_Bool GetCSSScale([in] PP_Resource resource,

[brettw, 2012/06/18 21:17:24]

Ditto on the return value.

[Josh Horwich, 2012/06/19 02:01:04]

Done.

+                      [out] float_t css_scale);
+};
+