<![CDATA[QMatrix4x4 multiply order]]>Hi,

I have a question about the QMatrix4x4 class.

This example code:

QMatrix4x4 test;
test.perspective(...); // projection
test.lookat(...); // view

What kind of matrix is test at the end? is it something like that:
identity * projection * view
or is it like that:
view * projection * identity

]]>https://forum.qt.io/topic/74216/qmatrix4x4-multiply-orderRSS for NodeWed, 20 May 2026 16:17:00 GMTMon, 12 Dec 2016 12:54:02 GMT60<![CDATA[Reply to QMatrix4x4 multiply order on Mon, 12 Dec 2016 18:27:35 GMT]]>QMatrix4x4 tmp = ...; tmp.translate(10,0,0);

results in

tmp = tmp * translationmatrix

So the correct answer seams to be

  1. identity * projection * view
]]>https://forum.qt.io/post/364095https://forum.qt.io/post/364095Mon, 12 Dec 2016 18:27:35 GMT<![CDATA[Reply to QMatrix4x4 multiply order on Mon, 12 Dec 2016 16:52:36 GMT]]>It's quite easy just to test it...
run

QMatrix4x4 test;
test.perspective(...); // projection

check what is in test.

QMatrix4x4 test;
test.lookat(...); // view

check what is in test.
pre and post multiply these two by hand (you can use wolframalpha) and compare it to the result you get in

QMatrix4x4 test;
test.perspective(...); // projection
test.lookat(...); // view
]]>https://forum.qt.io/post/364082https://forum.qt.io/post/364082Mon, 12 Dec 2016 16:52:36 GMT<![CDATA[Reply to QMatrix4x4 multiply order on Mon, 12 Dec 2016 14:03:52 GMT]]>@QT-static-prgm said in QMatrix4x4 multiply order:

Since matrices don't commute in the general case and operate on the right-hand term I'd say the latter.

]]>https://forum.qt.io/post/364041https://forum.qt.io/post/364041Mon, 12 Dec 2016 14:03:52 GMT