1589204 - Matrix4x4Flagged::operator* implementation is incorrect

Status: RESOLVED FIXED

(Core :: Graphics, defect)

Description

[Botond Ballo [:botond]]

While debugging a test failure for bug 1556556, I discovered a bug in Matrix4x4TypedFlagged::operator*(Matrix4x4Typed).

I was trying to multiply the following two matrices:

1 0 0 0
0 1 0 0
0 0 1 0
12 290 01

and

1.225 0 0 0
0 1.225 0 0
0 0 1 0
0 0 0 1

and getting this as the result:

1.225 0 0 0
0.12225 0 0
0 0 1 0 
14.7 355.25 0 0

The result is incorrect: the _44 element should be 1, not 0.

Comment 1

[Botond Ballo [:botond]]

The problem is on this line:

  matrix._44 = _41 * aMatrix._14 + _42 * aMatrix._24;

The full calculation would be:

  matrix._44 = _41 * aMatrix._14 + _42 * aMatrix._24 + _43 * aMatrix._34 + _44 * aMatrix._44;

Since this is MatrixType::Simple, we know that _43=0 and _44=1, so we can simplify this to:

  matrix._44 = _41 * aMatrix._14 + _42 * aMatrix._24 + aMatrix._44;

However, the calculation as written excludes the last term, aMatrix._44.

Comment 2

[Botond Ballo [:botond]]

Attachment: Bug 1589204 - Fix a bug in Matrix4x4Flagged::operator*. r=Bas,mstange

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/41a1dfdfea9f
Fix a bug in Matrix4x4Flagged::operator*. r=mstange

Comment 4

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/41a1dfdfea9f