From 1011b024c474d6becd74244540ebc5daed19c29a Mon Sep 17 00:00:00 2001
From: Botond Ballo <botond@mozilla.com>
Date: Tue, 5 May 2020 19:37:26 +0000
Subject: [PATCH] Bug 1556556 - Add some VisualToLayout() and LayoutToVisual()
 wrappers to ViewportUtils. r=kats

Differential Revision: https://phabricator.services.mozilla.com/D68724
---
 layout/base/ViewportUtils.cpp | 47 +++++++++++++++++++++++++++++++++++
 layout/base/ViewportUtils.h   | 17 +++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/layout/base/ViewportUtils.cpp b/layout/base/ViewportUtils.cpp
index d8f5050ef79d..2e8685d44c34 100644
--- a/layout/base/ViewportUtils.cpp
+++ b/layout/base/ViewportUtils.cpp
@@ -5,6 +5,7 @@
 #include "mozilla/PresShell.h"
 #include "mozilla/ViewportUtils.h"
 #include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/InputAPZContext.h"
 #include "mozilla/layers/ScrollableLayerGuid.h"
 #include "nsIContent.h"
 #include "nsLayoutUtils.h"
@@ -12,6 +13,7 @@
 namespace mozilla {
 
 using layers::APZCCallbackHelper;
+using layers::InputAPZContext;
 using layers::ScrollableLayerGuid;
 
 CSSToCSSMatrix4x4 ViewportUtils::GetVisualToLayoutTransform(
@@ -47,4 +49,49 @@ CSSToCSSMatrix4x4 ViewportUtils::GetVisualToLayoutTransform(
       .PostTranslate(transform.x, transform.y, 0);
 }
 
+CSSToCSSMatrix4x4 GetVisualToLayoutTransform(PresShell* aContext) {
+  ScrollableLayerGuid::ViewID targetScrollId =
+      InputAPZContext::GetTargetLayerGuid().mScrollId;
+  if (targetScrollId == ScrollableLayerGuid::NULL_SCROLL_ID) {
+    if (nsIFrame* rootScrollFrame = aContext->GetRootScrollFrame()) {
+      targetScrollId =
+          nsLayoutUtils::FindOrCreateIDFor(rootScrollFrame->GetContent());
+    }
+  }
+  return ViewportUtils::GetVisualToLayoutTransform(targetScrollId);
+}
+
+nsPoint ViewportUtils::VisualToLayout(const nsPoint& aPt, PresShell* aContext) {
+  auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
+  CSSPoint cssPt = CSSPoint::FromAppUnits(aPt);
+  cssPt = visualToLayout.TransformPoint(cssPt);
+  return CSSPoint::ToAppUnits(cssPt);
+}
+
+nsRect ViewportUtils::VisualToLayout(const nsRect& aRect, PresShell* aContext) {
+  auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
+  CSSRect cssRect = CSSRect::FromAppUnits(aRect);
+  cssRect = visualToLayout.TransformBounds(cssRect);
+  nsRect result = CSSRect::ToAppUnits(cssRect);
+
+  // In hit testing codepaths, the input rect often has dimensions of one app
+  // units. If we are zoomed in enough, the rounded size of the output rect
+  // can be zero app units, which will fail to Intersect() with anything, and
+  // therefore cause hit testing to fail. To avoid this, we expand the output
+  // rect to one app units.
+  if (!aRect.IsEmpty() && result.IsEmpty()) {
+    result.width = 1;
+    result.height = 1;
+  }
+
+  return result;
+}
+
+nsPoint ViewportUtils::LayoutToVisual(const nsPoint& aPt, PresShell* aContext) {
+  auto visualToLayout = mozilla::GetVisualToLayoutTransform(aContext);
+  CSSPoint cssPt = CSSPoint::FromAppUnits(aPt);
+  auto transformed = visualToLayout.Inverse().TransformPoint(cssPt);
+  return CSSPoint::ToAppUnits(transformed);
+}
+
 }  // namespace mozilla
\ No newline at end of file
diff --git a/layout/base/ViewportUtils.h b/layout/base/ViewportUtils.h
index 20e1bf2bd997..8fe2442a277d 100644
--- a/layout/base/ViewportUtils.h
+++ b/layout/base/ViewportUtils.h
@@ -8,8 +8,12 @@
 #include "Units.h"
 #include "mozilla/layers/ScrollableLayerGuid.h"
 
+class nsIFrame;
+
 namespace mozilla {
 
+class PresShell;
+
 class ViewportUtils {
  public:
   /* Return a transform to be applied to the coordinates of input events
@@ -32,6 +36,19 @@ class ViewportUtils {
        documentation for additional details. */
   static CSSToCSSMatrix4x4 GetVisualToLayoutTransform(
       layers::ScrollableLayerGuid::ViewID aScrollId);
+
+  /* The functions below apply GetVisualToLayoutTransform() or its inverse
+   * to various quantities.
+   *
+   * To determine the appropriate scroll id to pass into
+   * GetVisualToLayoutTransform(), these functions prefer to use the one
+   * from InputAPZContext::GetTargetLayerGuid() if one is available.
+   * If one is not available, they use the scroll id of the root scroll
+   * frame of the pres shell passed in as |aContext| as a fallback.
+   */
+  static nsPoint VisualToLayout(const nsPoint& aPt, PresShell* aContext);
+  static nsRect VisualToLayout(const nsRect& aRect, PresShell* aContext);
+  static nsPoint LayoutToVisual(const nsPoint& aPt, PresShell* aContext);
 };
 
 }  // namespace mozilla