gecko-dev/layout/style/nsStyleTransformMatrix.cpp

721 строка
25 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */
/*
* A class used for intermediate representations of the -moz-transform property.
*/
#include "nsStyleTransformMatrix.h"
#include "nsCSSValue.h"
#include "nsLayoutUtils.h"
#include "nsPresContext.h"
#include "nsRuleNode.h"
#include "nsSVGUtils.h"
#include "nsCSSKeywords.h"
#include "mozilla/StyleAnimationValue.h"
#include "gfxMatrix.h"
using namespace mozilla;
using namespace mozilla::gfx;
namespace nsStyleTransformMatrix {
/* Note on floating point precision: The transform matrix is an array
* of single precision 'float's, and so are most of the input values
* we get from the style system, but intermediate calculations
* involving angles need to be done in 'double'.
*/
// Define UNIFIED_CONTINUATIONS here and in nsDisplayList.cpp
// to have the transform property try
// to transform content with continuations as one unified block instead of
// several smaller ones. This is currently disabled because it doesn't work
// correctly, since when the frames are initially being reflowed, their
// continuations all compute their bounding rects independently of each other
// and consequently get the wrong value.
//#define UNIFIED_CONTINUATIONS
void
TransformReferenceBox::EnsureDimensionsAreCached()
{
if (mIsCached) {
return;
}
MOZ_ASSERT(mFrame);
mIsCached = true;
if (mFrame->GetStateBits() & NS_FRAME_SVG_LAYOUT) {
if (!nsLayoutUtils::SVGTransformBoxEnabled()) {
mX = -mFrame->GetPosition().x;
mY = -mFrame->GetPosition().y;
Size contextSize = nsSVGUtils::GetContextSize(mFrame);
mWidth = nsPresContext::CSSPixelsToAppUnits(contextSize.width);
mHeight = nsPresContext::CSSPixelsToAppUnits(contextSize.height);
} else
if (mFrame->StyleDisplay()->mTransformBox ==
NS_STYLE_TRANSFORM_BOX_FILL_BOX) {
// Percentages in transforms resolve against the SVG bbox, and the
// transform is relative to the top-left of the SVG bbox.
gfxRect bbox = nsSVGUtils::GetBBox(const_cast<nsIFrame*>(mFrame));
nsRect bboxInAppUnits =
nsLayoutUtils::RoundGfxRectToAppRect(bbox,
mFrame->PresContext()->AppUnitsPerCSSPixel());
// The mRect of an SVG nsIFrame is its user space bounds *including*
// stroke and markers, whereas bboxInAppUnits is its user space bounds
// including fill only. We need to note the offset of the reference box
// from the frame's mRect in mX/mY.
mX = bboxInAppUnits.x - mFrame->GetPosition().x;
mY = bboxInAppUnits.y - mFrame->GetPosition().y;
mWidth = bboxInAppUnits.width;
mHeight = bboxInAppUnits.height;
} else {
// The value 'border-box' is treated as 'view-box' for SVG content.
MOZ_ASSERT(mFrame->StyleDisplay()->mTransformBox ==
NS_STYLE_TRANSFORM_BOX_VIEW_BOX ||
mFrame->StyleDisplay()->mTransformBox ==
NS_STYLE_TRANSFORM_BOX_BORDER_BOX,
"Unexpected value for 'transform-box'");
// Percentages in transforms resolve against the width/height of the
// nearest viewport (or its viewBox if one is applied), and the
// transform is relative to {0,0} in current user space.
mX = -mFrame->GetPosition().x;
mY = -mFrame->GetPosition().y;
Size contextSize = nsSVGUtils::GetContextSize(mFrame);
mWidth = nsPresContext::CSSPixelsToAppUnits(contextSize.width);
mHeight = nsPresContext::CSSPixelsToAppUnits(contextSize.height);
}
return;
}
// If UNIFIED_CONTINUATIONS is not defined, this is simply the frame's
// bounding rectangle, translated to the origin. Otherwise, it is the
// smallest rectangle containing a frame and all of its continuations. For
// example, if there is a <span> element with several continuations split
// over several lines, this function will return the rectangle containing all
// of those continuations.
nsRect rect;
#ifndef UNIFIED_CONTINUATIONS
rect = mFrame->GetRect();
#else
// Iterate the continuation list, unioning together the bounding rects:
for (const nsIFrame *currFrame = mFrame->FirstContinuation();
currFrame != nullptr;
currFrame = currFrame->GetNextContinuation())
{
// Get the frame rect in local coordinates, then translate back to the
// original coordinates:
rect.UnionRect(result, nsRect(currFrame->GetOffsetTo(mFrame),
currFrame->GetSize()));
}
#endif
mX = 0;
mY = 0;
mWidth = rect.Width();
mHeight = rect.Height();
}
void
TransformReferenceBox::Init(const nsSize& aDimensions)
{
MOZ_ASSERT(!mFrame && !mIsCached);
mX = 0;
mY = 0;
mWidth = aDimensions.width;
mHeight = aDimensions.height;
mIsCached = true;
}
float
ProcessTranslatePart(const nsCSSValue& aValue,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox* aRefBox,
TransformReferenceBox::DimensionGetter aDimensionGetter)
{
nscoord offset = 0;
float percent = 0.0f;
if (aValue.GetUnit() == eCSSUnit_Percent) {
percent = aValue.GetPercentValue();
} else if (aValue.GetUnit() == eCSSUnit_Pixel ||
aValue.GetUnit() == eCSSUnit_Number) {
// Handle this here (even though nsRuleNode::CalcLength handles it
// fine) so that callers are allowed to pass a null style context
// and pres context to SetToTransformFunction if they know (as
// StyleAnimationValue does) that all lengths within the transform
// function have already been computed to pixels and percents.
//
// Raw numbers are treated as being pixels.
//
// Don't convert to aValue to AppUnits here to avoid precision issues.
return aValue.GetFloatValue();
} else if (aValue.IsCalcUnit()) {
nsRuleNode::ComputedCalc result =
nsRuleNode::SpecifiedCalcToComputedCalc(aValue, aContext, aPresContext,
aConditions);
percent = result.mPercent;
offset = result.mLength;
} else {
offset = nsRuleNode::CalcLength(aValue, aContext, aPresContext,
aConditions);
}
float translation = NSAppUnitsToFloatPixels(offset,
nsPresContext::AppUnitsPerCSSPixel());
// We want to avoid calling aDimensionGetter if there's no percentage to be
// resolved (for performance reasons - see TransformReferenceBox).
if (percent != 0.0f && aRefBox) {
translation += percent *
NSAppUnitsToFloatPixels((aRefBox->*aDimensionGetter)(),
nsPresContext::AppUnitsPerCSSPixel());
}
return translation;
}
/**
* Helper functions to process all the transformation function types.
*
* These take a matrix parameter to accumulate the current matrix.
*/
/* Helper function to process a matrix entry. */
static void
ProcessMatrix(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox)
{
NS_PRECONDITION(aData->Count() == 7, "Invalid array!");
gfxMatrix result;
/* Take the first four elements out of the array as floats and store
* them.
*/
result._11 = aData->Item(1).GetFloatValue();
result._12 = aData->Item(2).GetFloatValue();
result._21 = aData->Item(3).GetFloatValue();
result._22 = aData->Item(4).GetFloatValue();
/* The last two elements have their length parts stored in aDelta
* and their percent parts stored in aX[0] and aY[1].
*/
result._31 = ProcessTranslatePart(aData->Item(5),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Width);
result._32 = ProcessTranslatePart(aData->Item(6),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Height);
aMatrix = result * aMatrix;
}
static void
ProcessMatrix3D(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox)
{
NS_PRECONDITION(aData->Count() == 17, "Invalid array!");
Matrix4x4 temp;
temp._11 = aData->Item(1).GetFloatValue();
temp._12 = aData->Item(2).GetFloatValue();
temp._13 = aData->Item(3).GetFloatValue();
temp._14 = aData->Item(4).GetFloatValue();
temp._21 = aData->Item(5).GetFloatValue();
temp._22 = aData->Item(6).GetFloatValue();
temp._23 = aData->Item(7).GetFloatValue();
temp._24 = aData->Item(8).GetFloatValue();
temp._31 = aData->Item(9).GetFloatValue();
temp._32 = aData->Item(10).GetFloatValue();
temp._33 = aData->Item(11).GetFloatValue();
temp._34 = aData->Item(12).GetFloatValue();
temp._44 = aData->Item(16).GetFloatValue();
temp._41 = ProcessTranslatePart(aData->Item(13),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Width);
temp._42 = ProcessTranslatePart(aData->Item(14),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Height);
temp._43 = ProcessTranslatePart(aData->Item(15),
aContext, aPresContext, aConditions,
nullptr);
aMatrix = temp * aMatrix;
}
/* Helper function to process two matrices that we need to interpolate between */
void
ProcessInterpolateMatrix(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox,
bool* aContains3dTransform)
{
NS_PRECONDITION(aData->Count() == 4, "Invalid array!");
Matrix4x4 matrix1, matrix2;
if (aData->Item(1).GetUnit() == eCSSUnit_List) {
matrix1 = nsStyleTransformMatrix::ReadTransforms(aData->Item(1).GetListValue(),
aContext, aPresContext,
aConditions,
aRefBox, nsPresContext::AppUnitsPerCSSPixel(),
aContains3dTransform);
}
if (aData->Item(2).GetUnit() == eCSSUnit_List) {
matrix2 = ReadTransforms(aData->Item(2).GetListValue(),
aContext, aPresContext,
aConditions,
aRefBox, nsPresContext::AppUnitsPerCSSPixel(),
aContains3dTransform);
}
double progress = aData->Item(3).GetPercentValue();
aMatrix =
StyleAnimationValue::InterpolateTransformMatrix(matrix1, matrix2, progress)
* aMatrix;
}
/* Helper function to process a translatex function. */
static void
ProcessTranslateX(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
Point3D temp;
temp.x = ProcessTranslatePart(aData->Item(1),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Width);
aMatrix.PreTranslate(temp);
}
/* Helper function to process a translatey function. */
static void
ProcessTranslateY(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
Point3D temp;
temp.y = ProcessTranslatePart(aData->Item(1),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Height);
aMatrix.PreTranslate(temp);
}
static void
ProcessTranslateZ(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
Point3D temp;
temp.z = ProcessTranslatePart(aData->Item(1), aContext,
aPresContext, aConditions,
nullptr);
aMatrix.PreTranslate(temp);
}
/* Helper function to process a translate function. */
static void
ProcessTranslate(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox)
{
NS_PRECONDITION(aData->Count() == 2 || aData->Count() == 3, "Invalid array!");
Point3D temp;
temp.x = ProcessTranslatePart(aData->Item(1),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Width);
/* If we read in a Y component, set it appropriately */
if (aData->Count() == 3) {
temp.y = ProcessTranslatePart(aData->Item(2),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Height);
}
aMatrix.PreTranslate(temp);
}
static void
ProcessTranslate3D(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox)
{
NS_PRECONDITION(aData->Count() == 4, "Invalid array!");
Point3D temp;
temp.x = ProcessTranslatePart(aData->Item(1),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Width);
temp.y = ProcessTranslatePart(aData->Item(2),
aContext, aPresContext, aConditions,
&aRefBox, &TransformReferenceBox::Height);
temp.z = ProcessTranslatePart(aData->Item(3),
aContext, aPresContext, aConditions,
nullptr);
aMatrix.PreTranslate(temp);
}
/* Helper function to set up a scale matrix. */
static void
ProcessScaleHelper(Matrix4x4& aMatrix,
float aXScale,
float aYScale,
float aZScale)
{
aMatrix.PreScale(aXScale, aYScale, aZScale);
}
/* Process a scalex function. */
static void
ProcessScaleX(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2, "Bad array!");
ProcessScaleHelper(aMatrix, aData->Item(1).GetFloatValue(), 1.0f, 1.0f);
}
/* Process a scaley function. */
static void
ProcessScaleY(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2, "Bad array!");
ProcessScaleHelper(aMatrix, 1.0f, aData->Item(1).GetFloatValue(), 1.0f);
}
static void
ProcessScaleZ(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2, "Bad array!");
ProcessScaleHelper(aMatrix, 1.0f, 1.0f, aData->Item(1).GetFloatValue());
}
static void
ProcessScale3D(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 4, "Bad array!");
ProcessScaleHelper(aMatrix,
aData->Item(1).GetFloatValue(),
aData->Item(2).GetFloatValue(),
aData->Item(3).GetFloatValue());
}
/* Process a scale function. */
static void
ProcessScale(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2 || aData->Count() == 3, "Bad array!");
/* We either have one element or two. If we have one, it's for both X and Y.
* Otherwise it's one for each.
*/
const nsCSSValue& scaleX = aData->Item(1);
const nsCSSValue& scaleY = (aData->Count() == 2 ? scaleX :
aData->Item(2));
ProcessScaleHelper(aMatrix,
scaleX.GetFloatValue(),
scaleY.GetFloatValue(),
1.0f);
}
/* Helper function that, given a set of angles, constructs the appropriate
* skew matrix.
*/
static void
ProcessSkewHelper(Matrix4x4& aMatrix, double aXAngle, double aYAngle)
{
aMatrix.SkewXY(aXAngle, aYAngle);
}
/* Function that converts a skewx transform into a matrix. */
static void
ProcessSkewX(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_ASSERTION(aData->Count() == 2, "Bad array!");
ProcessSkewHelper(aMatrix, aData->Item(1).GetAngleValueInRadians(), 0.0);
}
/* Function that converts a skewy transform into a matrix. */
static void
ProcessSkewY(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_ASSERTION(aData->Count() == 2, "Bad array!");
ProcessSkewHelper(aMatrix, 0.0, aData->Item(1).GetAngleValueInRadians());
}
/* Function that converts a skew transform into a matrix. */
static void
ProcessSkew(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_ASSERTION(aData->Count() == 2 || aData->Count() == 3, "Bad array!");
double xSkew = aData->Item(1).GetAngleValueInRadians();
double ySkew = (aData->Count() == 2
? 0.0 : aData->Item(2).GetAngleValueInRadians());
ProcessSkewHelper(aMatrix, xSkew, ySkew);
}
/* Function that converts a rotate transform into a matrix. */
static void
ProcessRotateZ(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
double theta = aData->Item(1).GetAngleValueInRadians();
aMatrix.RotateZ(theta);
}
static void
ProcessRotateX(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
double theta = aData->Item(1).GetAngleValueInRadians();
aMatrix.RotateX(theta);
}
static void
ProcessRotateY(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
double theta = aData->Item(1).GetAngleValueInRadians();
aMatrix.RotateY(theta);
}
static void
ProcessRotate3D(Matrix4x4& aMatrix, const nsCSSValue::Array* aData)
{
NS_PRECONDITION(aData->Count() == 5, "Invalid array!");
double theta = aData->Item(4).GetAngleValueInRadians();
float x = aData->Item(1).GetFloatValue();
float y = aData->Item(2).GetFloatValue();
float z = aData->Item(3).GetFloatValue();
Matrix4x4 temp;
temp.SetRotateAxisAngle(x, y, z, theta);
aMatrix = temp * aMatrix;
}
static void
ProcessPerspective(Matrix4x4& aMatrix,
const nsCSSValue::Array* aData,
nsStyleContext *aContext,
nsPresContext *aPresContext,
RuleNodeCacheConditions& aConditions)
{
NS_PRECONDITION(aData->Count() == 2, "Invalid array!");
float depth = ProcessTranslatePart(aData->Item(1), aContext,
aPresContext, aConditions,
nullptr);
aMatrix.Perspective(depth);
}
/**
* SetToTransformFunction is essentially a giant switch statement that fans
* out to many smaller helper functions.
*/
static void
MatrixForTransformFunction(Matrix4x4& aMatrix,
const nsCSSValue::Array * aData,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox,
bool* aContains3dTransform)
{
MOZ_ASSERT(aContains3dTransform);
NS_PRECONDITION(aData, "Why did you want to get data from a null array?");
// It's OK if aContext and aPresContext are null if the caller already
// knows that all length units have been converted to pixels (as
// StyleAnimationValue does).
/* Get the keyword for the transform. */
switch (TransformFunctionOf(aData)) {
case eCSSKeyword_translatex:
ProcessTranslateX(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox);
break;
case eCSSKeyword_translatey:
ProcessTranslateY(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox);
break;
case eCSSKeyword_translatez:
*aContains3dTransform = true;
ProcessTranslateZ(aMatrix, aData, aContext, aPresContext,
aConditions);
break;
case eCSSKeyword_translate:
ProcessTranslate(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox);
break;
case eCSSKeyword_translate3d:
*aContains3dTransform = true;
ProcessTranslate3D(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox);
break;
case eCSSKeyword_scalex:
ProcessScaleX(aMatrix, aData);
break;
case eCSSKeyword_scaley:
ProcessScaleY(aMatrix, aData);
break;
case eCSSKeyword_scalez:
*aContains3dTransform = true;
ProcessScaleZ(aMatrix, aData);
break;
case eCSSKeyword_scale:
ProcessScale(aMatrix, aData);
break;
case eCSSKeyword_scale3d:
*aContains3dTransform = true;
ProcessScale3D(aMatrix, aData);
break;
case eCSSKeyword_skewx:
ProcessSkewX(aMatrix, aData);
break;
case eCSSKeyword_skewy:
ProcessSkewY(aMatrix, aData);
break;
case eCSSKeyword_skew:
ProcessSkew(aMatrix, aData);
break;
case eCSSKeyword_rotatex:
*aContains3dTransform = true;
ProcessRotateX(aMatrix, aData);
break;
case eCSSKeyword_rotatey:
*aContains3dTransform = true;
ProcessRotateY(aMatrix, aData);
break;
case eCSSKeyword_rotatez:
*aContains3dTransform = true;
case eCSSKeyword_rotate:
ProcessRotateZ(aMatrix, aData);
break;
case eCSSKeyword_rotate3d:
*aContains3dTransform = true;
ProcessRotate3D(aMatrix, aData);
break;
case eCSSKeyword_matrix:
ProcessMatrix(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox);
break;
case eCSSKeyword_matrix3d:
*aContains3dTransform = true;
ProcessMatrix3D(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox);
break;
case eCSSKeyword_interpolatematrix:
ProcessInterpolateMatrix(aMatrix, aData, aContext, aPresContext,
aConditions, aRefBox,
aContains3dTransform);
break;
case eCSSKeyword_perspective:
*aContains3dTransform = true;
ProcessPerspective(aMatrix, aData, aContext, aPresContext,
aConditions);
break;
default:
NS_NOTREACHED("Unknown transform function!");
}
}
/**
* Return the transform function, as an nsCSSKeyword, for the given
* nsCSSValue::Array from a transform list.
*/
nsCSSKeyword
TransformFunctionOf(const nsCSSValue::Array* aData)
{
MOZ_ASSERT(aData->Item(0).GetUnit() == eCSSUnit_Enumerated);
return aData->Item(0).GetKeywordValue();
}
Matrix4x4
ReadTransforms(const nsCSSValueList* aList,
nsStyleContext* aContext,
nsPresContext* aPresContext,
RuleNodeCacheConditions& aConditions,
TransformReferenceBox& aRefBox,
float aAppUnitsPerMatrixUnit,
bool* aContains3dTransform)
{
Matrix4x4 result;
for (const nsCSSValueList* curr = aList; curr != nullptr; curr = curr->mNext) {
const nsCSSValue &currElem = curr->mValue;
if (currElem.GetUnit() != eCSSUnit_Function) {
NS_ASSERTION(currElem.GetUnit() == eCSSUnit_None &&
!aList->mNext,
"stream should either be a list of functions or a "
"lone None");
continue;
}
NS_ASSERTION(currElem.GetArrayValue()->Count() >= 1,
"Incoming function is too short!");
/* Read in a single transform matrix. */
MatrixForTransformFunction(result, currElem.GetArrayValue(), aContext,
aPresContext, aConditions, aRefBox,
aContains3dTransform);
}
float scale = float(nsPresContext::AppUnitsPerCSSPixel()) / aAppUnitsPerMatrixUnit;
result.PreScale(1/scale, 1/scale, 1/scale);
result.PostScale(scale, scale, scale);
return result;
}
} // namespace nsStyleTransformMatrix