1 files changed, 71 insertions, 0 deletions
diff --git a/widget/DimensionRequest.h b/widget/DimensionRequest.h
new file mode 100644
index 0000000000..75f5c96b45
--- /dev/null
+++ b/widget/DimensionRequest.h
@@ -0,0 +1,71 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_DimensionRequest_h
+#define mozilla_DimensionRequest_h
+
+#include "Units.h"
+#include "mozilla/Maybe.h"
+
+class nsIBaseWindow;
+class nsIDocShellTreeOwner;
+
+namespace mozilla {
+
+enum class DimensionKind { Inner, Outer };
+
+/**
+ * DimensionRequest allows to request the change of some dimensions without
+ * having to specify the unchanged dimensions. This is specifically necessary
+ * when a change is initiated from a child process, which might not have an
+ * up-to-date view of its latest dimensions. Having to specify the missing
+ * dimensions with an outdated view can revert a previous change.
+ *
+ * The following series of changes `window.screenX = 10; window.screenY = 10;`
+ * essentially translates into two moveTo() calls. For the second call we want
+ * to account for changes made by the first call. From a child process we would
+ * end up crafting the second call without knowing the results of the first
+ * call. In the parent process we have access to results of the first call
+ * before crafting the second one. Although on Linux even the parent process
+ * doesn't have immediate access to the results of the last change.
+ *
+ * Note: The concept of an inner position is not present on
+ * nsIDocShellTreeOwner and nsIBaseWindow. A request specifying an inner
+ * position will return an NS_ERROR_NOT_IMPLEMENTED.
+ */
+struct DimensionRequest {
+  DimensionKind mDimensionKind;
+  Maybe<LayoutDeviceIntCoord> mX;
+  Maybe<LayoutDeviceIntCoord> mY;
+  Maybe<LayoutDeviceIntCoord> mWidth;
+  Maybe<LayoutDeviceIntCoord> mHeight;
+
+  /**
+   * Fills the missing dimensions with values obtained from `aSource`. Whether
+   * inner dimensions are supported depends on the implementation of
+   * `nsIBaseWindow::GetDimensions` for `aSource`.
+   *
+   * @param aSource  The source for the missing dimensions.
+   */
+  nsresult SupplementFrom(nsIBaseWindow* aSource);
+
+  /**
+   * Changes the outer size and or position of `aTarget`. Only outer dimensions
+   * are supported.
+   *
+   * @param aTarget  The target whose size or position we want to change.
+   */
+  nsresult ApplyOuterTo(nsIBaseWindow* aTarget);
+
+  /**
+   * Changes the inner size of `aTarget`. Only inner dimensions are supported.
+   *
+   * @param aTarget  The target whose size we want to change.
+   */
+  nsresult ApplyInnerTo(nsIDocShellTreeOwner* aTarget, bool aAsRootShell);
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_DimensionRequest_h