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[Poll] Managing my limited free time while job seeking
tom_mai78101 replied to tom_mai78101's topic in GDNet Lounge
Problem is, I get turned down for internships because they are mostly looking for undergraduates who are still in school, instead of me who is in the transitioning phase from Masters to Doctorate. 
I'm polling to see what choices can I make during my spare time, while I'm looking for a job. I'm a recent graduate, so I no longer am in school. I feel like I need to brush up on some of the stuffs taught in class, but another part of me felt like finishing up on the opensource project that I'm working on. What to choose? If anyone have a better choice for me to do something else more productive, which also benefits me while job seeking, please specify, so I can take a look.

What is the Quaternion equivalent for multiplying two 3x3 rotation matrices together?
tom_mai78101 replied to tom_mai78101's topic in Math and Physics
Ah, it seems I was missing a conjugate to achieve rotation multiplication with quaternions. No wonder I was confused about this. I will heed your warning. Is there anything else I am missing in regards to quaternion alternatives to rotation matrix multiplications? 
What is the Quaternion equivalent for multiplying two 3x3 rotation matrices together?
tom_mai78101 replied to tom_mai78101's topic in Math and Physics
The order I'm using is the order going from the left to the right. Same with the example I used in the GIF at the very top. I thought I was consistent enough and therefore there's no need to explain or define the multiplication order for both the Mat3x3 and the quaternions. Sorry. As for the code snippet I mentioned, I was referring to your quote saying: To me, it sounds like you were referring that, assuming the order of operations is exactly the same (going from left to right, and the placement is result = old * new The pattern of the following operation: Mat3x3 result = Mat3x3 old * Mat3x3 new, where operator* denotes the multiplication, and Mat3x3 is the type. Is exactly the same, literally and logically, as the following operation (just the pattern): Quaternion result = Quaternion old * Quaternion new, where operator* denotes the multiplication, and Quaternion is the type. I would like to seek clarification on this. Thanks again. 
What is the Quaternion equivalent for multiplying two 3x3 rotation matrices together?
tom_mai78101 replied to tom_mai78101's topic in Math and Physics
So, this is correct? // Generate new local_rotation, matrixwise // local_rotation = rotation matrix representing the current orientation // new_rotation = rotation matrix representing the difference. (Rotation difference from new_rotation to local_rotation). // total = rotation matrix representing (the final new orientation) total = local_rotation * new_rotation // Generate new local_rotation, quaternionwise // local_rotation = quaternion representing the current orientiation. // total = quaternion representing (the local_rotation + the difference from the old orientation to the the final new orientation.) total = local_rotation * total 
What is the Quaternion equivalent for multiplying two 3x3 rotation matrices together?
tom_mai78101 posted a topic in Math and Physics
Let's say you have a 3x3 matrix that stores an object's current rotation. As we know, by multiplying it with a new 3x3 rotation matrix, we will get a brand new rotation matrix. newMat3x3 = Mat3x3A * Mat3x3B. Now, I have came across an issue where I see Mat3x3 rotation matrix being multiplied together to form the spinning cube, shown above. But the device that I'm using has limited memory, prompting me to figure out (and struggling along the way) to find an alternative to multiplying rotation matrices using quaternions (since it saves memory). In other words, I would like to replace rotation matrices with quaternions, but I don't know what is the quaternion equivalent to 2 rotation matrices multiplied together. What is the quaternion equivalent to Mat3x3 * Mat3x3, or rotation matrix multiplications? PS: I mashed 2 copies of the same cube together, so it is directly overlapping each other. One of the cubes is not spinning, because that cube is used for implementing the quaternion alternative method, but the method is not complete, so the orientation is set to its quaternion identity. So, no, it's not a graphical glitch, but an intentional test. 
Porting a physics engine: What do these variables stand for?
tom_mai78101 replied to tom_mai78101's topic in General and Gameplay Programming
Yep, just added them in. Unfortunately I didn't come up with the names for a lot of these things. Extent. Incident. Bleh. Also it's much easier to just derive things on paper and copy down into the code the equations, so a lot of abstract symbols come up, like e and whatnot. Apologies if any of that is confusing. Hopefully, some of the issues/pull requests are handled. I noticed there is one which resolved some other confusing parts in your code, but I have no idea if it is better. Thanks again. 
Porting a physics engine: What do these variables stand for?
tom_mai78101 replied to tom_mai78101's topic in General and Gameplay Programming
Not sure. Nonetheless, yay! Thanks. 
Porting a physics engine: What do these variables stand for?
tom_mai78101 replied to tom_mai78101's topic in General and Gameplay Programming
Oh, that's even better. Thanks, and I'll try my best to fetch the answers for this thread, so future readers will be able to see them. 
Porting a physics engine: What do these variables stand for?
tom_mai78101 posted a topic in General and Gameplay Programming
I'm currently porting / learning C++ code of a lightweight physics engine over to a C code variant engine. The lightweight physics engine is qu3e, written by Randy Gaul. Source code While porting the code over, I spot a few things that I'm confused about. Given that there are no comments that explain what these variables are for, and doesn't say what their meanings are, I am asking for help to explain the meaning and intentions for these variables. _____________________________________________________ Here's one. I know Feature Pairs in a physics engine refers to "The closest pair of features (edge or vertex)". So I am confused about what inR, inI, outR, and outI stands for. What do these 4 variables have to do with Feature Pairs? _____________________________________________________ This is another one. In this context, I know this struct is referred to as the AxisAligned Bounding Box struct, or AABB. Even with that in mind, I still have no idea what the e variable represents in the AABBes. Is there something important about the letter "e", as in, it could be some mathematical constant? Or is it energy? 
Best method of reading 4x4 matrices of various orientations?
tom_mai78101 replied to tom_mai78101's topic in General and Gameplay Programming
The question is asking about human readability, to read the various matrix orientations in a way that the method can be applied to all situations. So, when the human is reading the line of code and picturing the numbers, the human will project the relations for each member of the matrix by referring it to the mathematical representation of an ideal matrix that the human has a preference over. In other words, since every developers have their own ways of piecing the matrix data together in their minds, one of which is "considered" better than the other based on preference, I am proposing a shortcut method interpreting the data into a very highlevel concept that the human can grasp, and can be "translated" to their respective context given for various libraries. I have this idea when I was working on a 3D graphics library, and I still have trouble grasping the concept of a different matrix orientation that I'm unfamiliar with my math textbook mathematical representation. Whenever I make a big change to a matrix math function, I would sometimes get told the matrix is inadvertently transposed than it was intended, and that kind of confusion would lead me to frustrating debugging situations. With this method I proposed, I find reading matrices in my head a bit easier to do. I'm very sure there are more better methods than my idea. 
Best method of reading 4x4 matrices of various orientations?
tom_mai78101 posted a topic in General and Gameplay Programming
When I say "reading", I meant to say, "reading the line of code and picturing the numbers in relations to what each member of the matrix is referring to." This is not referred to as "a compiler reading the lines of code.". I have come across an interesting observation where there are many orientations of a written 4x4 matrix. Some matrices used in some libraries are shown as: [0] [4] [8] [12] [1] [5] [9] [13] [2] [6] [10] [14] [3] [7] [11] [15] And some matrices are shown as: [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] For rowmajor and columnmajor matrices, they would also have orientations laid out as either one of these: [1] [0] [0] [0] [0] [1] [0] [0] [0] [0] [1] [0] [0] [0] [0] [1] [0] [0] [0] [1] [0] [0] [1] [0] [0] [1] [0] [0] [1] [0] [0] [0] Depending on Big Endian or Little Endian order. Do note that I am unsure of this, as to why the diagonals of the matrix is forward/backward slanting, depending on how the graphics chipset on various devices reads the data structure. I'm assuming it to be Big / Little Endian based on the reading order of the memory. Combining these findings, I can see there are 4 types of matrix orientations commonly used in various libraries for various devices/applications. I want to know if my proposed method below is the best method of reading these various matrix orientations, and holds the concept:  For instance, given the following matrix: [0] [4] [8] [12] [1] [5] [9] [13] [2] [6] [10] [14] [3] [7] [11] [15] We can assume this is the case in an OpenGL environment: RT = right UP = up BK = back POS = position/translation US = uniform scale [RT.x] [UP.x] [BK.x] [POS.x] [RT.y] [UP.y] [BK.y] [POS.y] [RT.z] [UP.z] [BK.z] [POS.Z] [ ] [ ] [ ] [US ] To humanly read a matrix, instead of looking at the matrix aligned in a 4x4 grid, we should look at each individual elements used in the matrix, as if the matrix is an array. [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] This means, by reordering our matrix to the following: [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] And knowing the relations of each member element of the matrix as: RT = right UP = up BK = back POS = position/translation US = uniform scale [RT.x] [RT.y] [RT.z] [ ] [UP.x] [UP.y] [UP.z] [ ] [BK.x] [BK.y] [BK.z] [ ] [POS.x] [POS.y] [POS.Z] [ US ] We can let a human read all matrix orientations by mapping the indices of the array to the associated properties of the matrix: [0..2] = RT [4..6] = UP [8..10] = BK [12..14] = POS [15] = US And read the indices in reverse/forward for each subarray based on Big or Little Endian. This, in turn, can be easier to translate into code for the compiler to read, without worrying about any various 4x4 matrix orientations. 
[VS2015] Downgrade to update 1
tom_mai78101 replied to Juliean's topic in General and Gameplay Programming
I am on Update 3, and I haven't seen uproars about VS 2015 being completely broken lately. (Unless I'm looking in the wrong places at the wrong times.) I believed the only way for you to revert/downgrade to Update 1 is if you reinstall VS 2015, then update to Update 1. Use the official Visual Studio uninstaller, linked here, for the best possible results.

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