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uglybdavis

Member Since 06 Mar 2012
Offline Last Active Feb 26 2015 02:26 PM

Posts I've Made

In Topic: Confused about row major matrix and pre multiplication

25 February 2015 - 01:18 AM

Thank you!

 

That has answered all of my questions. Thanks again, you have no idea how helpful that all was!


In Topic: Confused about row major matrix and pre multiplication

25 February 2015 - 12:03 AM

That's very helpful. 

 

If i understand what you said correctly, if two matrices (A and B) together; to find element 2,3 of the resulting matrix

 

Row major multiplication: take the dot product row 2 of matrix A and column 3 of matrix B

 

Column major multiplication: take the dot product of column 2 of matrix A, and row 3 of matrix B

 

----------------------------------------

 

So, last question (i hope). Does the above mean that the formula for matrix product (For matrices F & G):

image17.gif?_subject_uid=48598159&w=AACC

 

This will always take dot product the i-th row and j-th column of the two matrices, the only difference being that row major = FG, while column major = GF

 

OR, do the subscripts get a different meaning? Like in row major it's the i-th row and j-th column, where with column major it's the j-th row and i-th column?


In Topic: Confused about row major matrix and pre multiplication

24 February 2015 - 07:48 PM

I see, thank you for clearing that up. 
 
If i understand correctly, the transpose is a result of treating the vector as a column vector; hence the matrix is never actually transposed. Is that correct?
 
I have one more question regarding pre / post multiplication. I always assumed that the whole row v column order was what determined if pre or post multiplication is used (Due largely to my understanding of linear algebra being based on the differences in OpenGL & Direct X). 
 
Now that i'm trying to build some more solid mathematical foundations i find my old understanding very chalenged.
 
If we have Matrix T (a translation matrix that translates by 10, 20 and 30) 
and matrix S (A scale matrix that is a uniform scale of two)
 
And we want to concatinate the transformation so that the matrix translates first, and scales second we must calculate it as S x T.
This is assuming the same multiplication method as in the first post. I think because we scaled first then translated this is using post multiplication?
 
If correct, how come post multiplying two row major matrices works in math but Direct 3D uses pre-multiplication? Is this due to some implicit like the vector X matrix multiplication? Am i missing something trivial in my mental model of how this works?
 
Or perhaps is my pre / post terminology wrong when it comes to multiplying matrices?

In Topic: Game Engine for Linux

20 February 2015 - 07:16 PM

@phantom

I totally forgot UE4 is on linux now!

 

@alnite

It's just in blender. You're gonna have to do some googling. Tough as phantom pointed out, UE4 man! Should be super quick to prototype with blueprints.


In Topic: Game Engine for Linux

20 February 2015 - 02:40 PM

Game Editor

Blender Game Engine

Godot

C4


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