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Bug 1057578 - Make the overscroll transform a uniform stretch. r=kats
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Botond Ballo
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@ -978,8 +978,7 @@ pref("apz.subframe.enabled", true);
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pref("apz.overscroll.enabled", true);
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pref("apz.overscroll.fling_friction", "0.02");
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pref("apz.overscroll.fling_stopped_threshold", "0.4");
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pref("apz.overscroll.clamping", "0.5");
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pref("apz.overscroll.z_effect", "0.5");
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pref("apz.overscroll.stretch_factor", "0.5");
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pref("apz.overscroll.snap_back.spring_stiffness", "0.6");
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pref("apz.overscroll.snap_back.spring_friction", "0.1");
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pref("apz.overscroll.snap_back.mass", "1200");
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@ -248,16 +248,11 @@ typedef mozilla::gfx::Matrix4x4 Matrix4x4;
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* number, we stop the fling.
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* Units: screen pixels per millisecond
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*
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* "apz.overscroll.clamping"
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* The maximum proportion of the composition bounds which can become blank
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* as a result of overscroll, along the axis of overscroll.
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*
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* "apz.overscroll.z_effect"
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* The fraction of "apz.overscroll.clamping" which can become blank as a result
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* of overscroll, along the axis opposite to the axis of overscroll. Called
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* "z_effect" because the shrinking that brings about the blank space on the
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* opposite axis creates the effect of the page moving away from you along a
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* "z" axis.
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* "apz.overscroll.stretch_factor"
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* How much overscrolling can stretch content along an axis.
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* The maximum stretch along an axis is a factor of (1 + kStretchFactor).
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* (So if kStretchFactor is 0, you can't stretch at all; if kStretchFactor
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* is 1, you can stretch at most by a factor of 2).
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*
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* "apz.overscroll.snap_back.spring_stiffness"
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* The stiffness of the spring used in the physics model for the overscroll
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@ -2185,89 +2180,42 @@ bool AsyncPanZoomController::UpdateAnimation(const TimeStamp& aSampleTime,
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}
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void AsyncPanZoomController::GetOverscrollTransform(Matrix4x4* aTransform) const {
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// The overscroll effect is a combination of a translation in
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// the direction of overscroll, and shrinking in both directions.
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// With the effect applied, we can think of the composited region as being
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// made up of the following subregions.
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// (1) The shrunk content (or a portion of it) that used to fill the
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// composited region.
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// (2) The space created along the axis that has overscroll. This space is
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// blank, filled by the background color of the overscrolled content.
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// TODO(botond): Implement handling of background color.
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// (3) The space created along the other axis. There may or may not be
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// content available to fill this space, depending on our scroll
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// position along this axis. If there is content, it's shown from the
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// displayport. (TODO: Currently we don't take any measures to ensure
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// that the displayport is large enough to have this content. Perhaps
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// we should.) Otherwise, these spaces are also blank like (2).
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// To illustrate, for the case where we are overscrolling past the top of
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// the page, these regions are (1) the bottom-centre region, (2) the top
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// regions, and (3) the bottom-left and bottom-right regions of the
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// composited area, respectively.
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// The overscroll effect is a uniform stretch along the overscrolled axis,
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// with the edge of the content where we have reached the end of the
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// scrollable area pinned into place.
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// The maximum proportion of the composition length which can become blank
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// space along an axis as we overscroll along that axis.
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const float kClamping = gfxPrefs::APZOverscrollClamping();
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// The kStretchFactor parameter determines how much overscroll can stretch the
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// content.
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const float kStretchFactor = gfxPrefs::APZOverscrollStretchFactor();
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// The proportion of the composition length which will become blank space
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// along each axis as a result of overscroll along that axis. Since
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// Axis::ApplyResistance() keeps the magnitude of the overscroll in the range
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// [0, GetCompositionLength()], these scale factors should be in the range
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// [0, kClamping].
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float spacePropX = kClamping * fabsf(mX.GetOverscroll()) / mX.GetCompositionLength();
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float spacePropY = kClamping * fabsf(mY.GetOverscroll()) / mY.GetCompositionLength();
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// Compute the amount of the stretch along each axis. The stretch is
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// proportional to the amount by which we are overscrolled along that axis.
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CSSSize compositionSize(mX.GetCompositionLength(), mY.GetCompositionLength());
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float scaleX = 1 + kStretchFactor * fabsf(mX.GetOverscroll()) / mX.GetCompositionLength();
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float scaleY = 1 + kStretchFactor * fabsf(mY.GetOverscroll()) / mY.GetCompositionLength();
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// The fraction of the proportions above which will become blank space along
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// the _opposite_ axis as we zoom out as a result of overscroll along an axis.
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// This creates a 3D effect, as in the layer were moving backward along a "z"
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// axis.
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const float kZEffect = gfxPrefs::APZOverscrollZEffect();
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// The translation to apply for overscroll along the x axis.
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CSSPoint translationX;
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if (mX.IsOverscrolled()) {
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// Keep the content centred vertically as we zoom out.
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translationX.y = (spacePropX * kZEffect * mY.GetCompositionLength()) / 2;
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if (mX.GetOverscroll() < 0) {
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// Overscroll on left.
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translationX.x = spacePropX * mX.GetCompositionLength();
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} else {
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// Overscroll on right.
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// Note that zooming out already moves the content at the right edge
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// of the composition bounds to the left, but since the zooming is
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// dampened by kZEffect, it doesn't take us as far as we want to go.
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translationX.x = - (spacePropX * (1 - kZEffect) * mX.GetCompositionLength());
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}
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// The scale is applied relative to the origin of the composition bounds, i.e.
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// it keeps the top-left corner of the content in place. This is fine if we
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// are overscrolling at the top or on the left, but if we are overscrolling
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// at the bottom or on the right, we want the bottom or right edge of the
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// content to stay in place instead, so we add a translation to compensate.
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CSSPoint translation;
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if (mX.IsOverscrolled() && mX.GetOverscroll() > 0) {
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// Overscrolled on the right.
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CSSCoord overscrolledCompositionWidth = scaleX * compositionSize.width;
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CSSCoord extraCompositionWidth = overscrolledCompositionWidth - compositionSize.width;
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translation.x = -extraCompositionWidth;
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}
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if (mY.IsOverscrolled() && mY.GetOverscroll() > 0) {
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// Overscrolled at the bottomn.
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CSSCoord overscrolledCompositionHeight = scaleY * compositionSize.height;
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CSSCoord extraCompositionHeight = overscrolledCompositionHeight - compositionSize.height;
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translation.y = -extraCompositionHeight;
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}
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// The translation to apply for overscroll along the y axis.
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CSSPoint translationY;
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if (mY.IsOverscrolled()) {
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// Keep the content centred horizontally as we zoom out.
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translationY.x = (spacePropY * kZEffect * mX.GetCompositionLength()) / 2;
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if (mY.GetOverscroll() < 0) {
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// Overscroll at top.
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translationY.y = spacePropY * mY.GetCompositionLength();
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} else {
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// Overscroll at bottom.
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// Note that zooming out already moves the content at the bottom edge
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// of the composition bounds up, but since the zooming is
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// dampened by kZEffect, it doesn't take us as far as we want to go.
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translationY.y = - (spacePropY * (1 - kZEffect) * mY.GetCompositionLength());
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}
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}
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// Combine the transformations along the two axes.
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float spaceProp = sqrtf(spacePropX * spacePropX + spacePropY * spacePropY);
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CSSPoint translation = translationX + translationY;
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float scale = 1 - (kZEffect * spaceProp);
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// Finally, create a matrix representing the transformations.
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// Combine the transformations into a matrix.
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ScreenPoint screenTranslation = translation * mFrameMetrics.GetZoom();
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*aTransform = Matrix4x4().Scale(scale, scale, 1)
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*aTransform = Matrix4x4().Scale(scaleX, scaleY, 1)
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.PostTranslate(screenTranslation.x, screenTranslation.y, 0);
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}
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@ -152,8 +152,7 @@ private:
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DECL_GFX_PREF(Live, "apz.overscroll.enabled", APZOverscrollEnabled, bool, false);
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DECL_GFX_PREF(Live, "apz.overscroll.fling_friction", APZOverscrollFlingFriction, float, 0.02f);
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DECL_GFX_PREF(Live, "apz.overscroll.fling_stopped_threshold", APZOverscrollFlingStoppedThreshold, float, 0.4f);
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DECL_GFX_PREF(Live, "apz.overscroll.clamping", APZOverscrollClamping, float, 0.5f);
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DECL_GFX_PREF(Live, "apz.overscroll.z_effect", APZOverscrollZEffect, float, 0.2f);
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DECL_GFX_PREF(Live, "apz.overscroll.stretch_factor", APZOverscrollStretchFactor, float, 0.5f);
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DECL_GFX_PREF(Live, "apz.overscroll.snap_back.spring_stiffness", APZOverscrollSnapBackSpringStiffness, float, 0.6f);
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DECL_GFX_PREF(Live, "apz.overscroll.snap_back.spring_friction", APZOverscrollSnapBackSpringFriction, float, 0.1f);
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DECL_GFX_PREF(Live, "apz.overscroll.snap_back.mass", APZOverscrollSnapBackMass, float, 1000.0f);
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@ -442,8 +442,7 @@ pref("apz.num_paint_duration_samples", 3);
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pref("apz.overscroll.enabled", false);
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pref("apz.overscroll.fling_friction", "0.02");
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pref("apz.overscroll.fling_stopped_threshold", "0.4");
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pref("apz.overscroll.clamping", "0.5");
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pref("apz.overscroll.z_effect", "0.2");
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pref("apz.overscroll.stretch_factor", "0.5");
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pref("apz.overscroll.snap_back.spring_stiffness", "0.6");
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pref("apz.overscroll.snap_back.spring_friction", "0.1");
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pref("apz.overscroll.snap_back.mass", "1000.0");
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