AuroraMiddleware/qt5base-lts
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

QMatrix4x4: fix aliasing problem in operator*=

Browse Source 
When multiplying a QMatrix4x4 by itself, we were clobbering the very
matrix we read from. Employ read-caching to avoid this aliasing problem.

[ChangeLog][QtGui][QMatrix4x4] operator*=() now calculates the correct
result even if the RHS and LHS are the same object.

Change-Id: I8534d56cfdd62c336577125127f05173fcec2873
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
This commit is contained in:
Marc Mutz 2017-04-14 12:39:20 +02:00
parent 98e0cb0a28
commit 5662234afa
2 changed files with 6 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
src/gui/math3d/qmatrix4x4.h
View File

@ -423,8 +423,9 @@ inline QMatrix4x4& QMatrix4x4::operator-=(const QMatrix4x4& other)
return *this;
}
inline QMatrix4x4& QMatrix4x4::operator*=(const QMatrix4x4& other)
inline QMatrix4x4& QMatrix4x4::operator*=(const QMatrix4x4& o)
{
const QMatrix4x4 other = o; // prevent aliasing when &o == this ### Qt 6: take o by value
flagBits |= other.flagBits;
if (flagBits < Rotation2D) {

4
tests/auto/gui/math3d/qmatrixnxn/tst_qmatrixnxn.cpp
View File

@ -1227,6 +1227,10 @@ void tst_QMatrixNxN::multiply4x4()
QMatrix4x4 m5;
m5 = m1 * m2;
QVERIFY(isSame(m5, (const float *)m3Values));
QMatrix4x4 m1xm1 = m1 * m1;
m1 *= m1;
QCOMPARE(m1, m1xm1);
}
// Test matrix multiplication for 4x3 matrices.