1 files changed, 164 insertions, 0 deletions
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/ScreenLength.java b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/ScreenLength.java
new file mode 100644
index 0000000000..1ce4b41659
--- /dev/null
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/ScreenLength.java
@@ -0,0 +1,164 @@
+/* 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/. */
+
+package org.mozilla.geckoview;
+
+import androidx.annotation.AnyThread;
+import androidx.annotation.IntDef;
+import androidx.annotation.NonNull;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * ScreenLength is a class that represents a length on the screen using different units. The default
+ * unit is a pixel. However lengths may be also represented by a dimension of the visual viewport or
+ * of the full scroll size of the root document.
+ */
+public class ScreenLength {
+  @Retention(RetentionPolicy.SOURCE)
+  @IntDef({PIXEL, VISUAL_VIEWPORT_WIDTH, VISUAL_VIEWPORT_HEIGHT, DOCUMENT_WIDTH, DOCUMENT_HEIGHT})
+  public @interface ScreenLengthType {}
+
+  /** Pixel units. */
+  public static final int PIXEL = 0;
+
+  /**
+   * Units are in visual viewport width. If the visual viewport is 100 pixels wide, then a value of
+   * 2.0 would represent a length of 200 pixels.
+   *
+   * @see <a href="https://developer.mozilla.org/en-US/docs/Glossary/Visual_Viewport">MDN Visual
+   *     Viewport</a>
+   */
+  public static final int VISUAL_VIEWPORT_WIDTH = 1;
+
+  /**
+   * Units are in visual viewport height. If the visual viewport is 100 pixels high, then a value of
+   * 2.0 would represent a length of 200 pixels.
+   *
+   * @see <a href="https://developer.mozilla.org/en-US/docs/Glossary/Visual_Viewport">MDN Visual
+   *     Viewport</a>
+   */
+  public static final int VISUAL_VIEWPORT_HEIGHT = 2;
+
+  /**
+   * Units represent the entire scrollable documents width. If the document is 1000 pixels wide then
+   * a value of 1.0 would represent 1000 pixels.
+   */
+  public static final int DOCUMENT_WIDTH = 3;
+
+  /**
+   * Units represent the entire scrollable documents height. If the document is 1000 pixels tall
+   * then a value of 1.0 would represent 1000 pixels.
+   */
+  public static final int DOCUMENT_HEIGHT = 4;
+
+  /**
+   * Create a ScreenLength of zero pixels length. Type is {@link #PIXEL}.
+   *
+   * @return ScreenLength of zero length.
+   */
+  @NonNull
+  @AnyThread
+  public static ScreenLength zero() {
+    return new ScreenLength(0.0, PIXEL);
+  }
+
+  /**
+   * Create a ScreenLength of zero pixels length. Type is {@link #PIXEL}. Can be used to scroll to
+   * the top of a page when used with PanZoomController.scrollTo()
+   *
+   * @return ScreenLength of zero length.
+   */
+  @NonNull
+  @AnyThread
+  public static ScreenLength top() {
+    return zero();
+  }
+
+  /**
+   * Create a ScreenLength of the documents height. Type is {@link #DOCUMENT_HEIGHT}. Can be used to
+   * scroll to the bottom of a page when used with {@link PanZoomController#scrollTo(ScreenLength,
+   * ScreenLength)}
+   *
+   * @return ScreenLength of document height.
+   */
+  @NonNull
+  @AnyThread
+  public static ScreenLength bottom() {
+    return new ScreenLength(1.0, DOCUMENT_HEIGHT);
+  }
+
+  /**
+   * Create a ScreenLength of a specific length. Type is {@link #PIXEL}.
+   *
+   * @param value Pixel length.
+   * @return ScreenLength of document height.
+   */
+  @NonNull
+  @AnyThread
+  public static ScreenLength fromPixels(final double value) {
+    return new ScreenLength(value, PIXEL);
+  }
+
+  /**
+   * Create a ScreenLength that uses the visual viewport width as units. Type is {@link
+   * #VISUAL_VIEWPORT_WIDTH}. Can be used with {@link PanZoomController#scrollBy(ScreenLength,
+   * ScreenLength)} to scroll a value of the width of visual viewport content.
+   *
+   * @param value Factor used to calculate length. A value of 2.0 would indicate a length twice as
+   *     long as the length of the visual viewports width.
+   * @return ScreenLength of specifying a length of value * visual viewport width.
+   */
+  @NonNull
+  @AnyThread
+  public static ScreenLength fromVisualViewportWidth(final double value) {
+    return new ScreenLength(value, VISUAL_VIEWPORT_WIDTH);
+  }
+
+  /**
+   * Create a ScreenLength that uses the visual viewport width as units. Type is {@link
+   * #VISUAL_VIEWPORT_HEIGHT}. Can be used with {@link PanZoomController#scrollBy(ScreenLength,
+   * ScreenLength)} to scroll a value of the height of visual viewport content.
+   *
+   * @param value Factor used to calculate length. A value of 2.0 would indicate a length twice as
+   *     long as the length of the visual viewports height.
+   * @return ScreenLength of specifying a length of value * visual viewport width.
+   */
+  @NonNull
+  @AnyThread
+  public static ScreenLength fromVisualViewportHeight(final double value) {
+    return new ScreenLength(value, VISUAL_VIEWPORT_HEIGHT);
+  }
+
+  private final double mValue;
+  @ScreenLengthType private final int mType;
+
+  /* package */ ScreenLength(final double value, @ScreenLengthType final int type) {
+    mValue = value;
+    mType = type;
+  }
+
+  /**
+   * Returns the scalar value used to calculate length. The units of the returned valued are defined
+   * by what is returned by {@link #getType()}
+   *
+   * @return Scalar value of the length.
+   */
+  @AnyThread
+  public double getValue() {
+    return mValue;
+  }
+
+  /**
+   * Returns the unit type of the length The length can be one of the following: {@link #PIXEL},
+   * {@link #VISUAL_VIEWPORT_WIDTH}, {@link #VISUAL_VIEWPORT_HEIGHT}, {@link #DOCUMENT_WIDTH},
+   * {@link #DOCUMENT_HEIGHT}
+   *
+   * @return Unit type of the length.
+   */
+  @AnyThread
+  @ScreenLengthType
+  public int getType() {
+    return mType;
+  }
+}