I have some questions about Transform and Matrix4 with animation in flutter, I need your help !
I have been confused of the concept of this for days. As the title, is the Transform.translate same as Matrix4.translate? I read the docs and implementation of these two methods. I found that Transform.translate simply change the entry 12, 13, 14 of Matrix4; however, Matrix4.translate is more complicated, it even changes the entry 15 of Matrix4. Does it mean they are different?
Originally, I think they are the same thing. But, why these two kinds of code generate different results: Code1 Code2
My last question is that in the code3, I tried to change the order of setEntry and rotateY methods, and I got different result on simulator. Why, I think they should be the same.
I think I am misunderstand the much concept about them, any advice is appreciated !!!
Thank you.
Related
I had another question about processing and a project i'm making. I would like to play a movie in a loop on the background. I managed to do this by initializing a Movie and putting it in an image the size of my app. But now I would like to load in multiple movies and add a button to change the background when pressed with the leap motion. Is this possible ? Or should I use a different library for this ?
Thanks in advance!
Kind regards,
DarthSwedo
It's really hard to answer general "how do I do this" type questions. Stack Overflow is designed more for specific "I tried X, expected Y, but got Z instead" type questions. You'll have much better luck if you just try something and post an MCVE if you get stuck.
That being said, I'm going to try to clear up some of the general confusion you seem to have.
Step 1: You need to figure out what library or libraries you're using. In all of your questions, you seem to not be sure which library you're using. Which Leap Motion library are you using? How did you set it up? Where is its documentation? You say you're using a Movie class. Where is that coming from? Are you sure it's not from the Video library?
If you have more specific questions in the future, please provide this information. We can't really help you without it. But more importantly, you need to know the answers to these questions if any of this is ever going to make any sense.
Step 2: Read the documentation for those libraries. Processing comes with the reference. The Video library comes with its own documentation page. I'm sure whatever Leap Motion library you're using has something similar. You need to read about the functions available to you. That's a huge part of programming. Right now your question is just asking whether something possible, and the honest answer to that is, well, what happened when you googled it?
Step 3: Try something. After you read through the documentation, just try something. Write some code based on the examples in the documentation. Even if that code doesn't work, that's okay, because then you can use it as an MCVE and ask a more specific question.
Good luck.
First of all, in this question I'd like to stay away from the polemic on whether source code commenting is good or bad. I'm just trying to understand more clearly what people mean when they talk about comments that tell you WHY, WHAT or HOW.
We often see guidelines like "Comments should tell you WHY; code itself should tell you HOW". It is easy to agree with the statement on an abstract level. However, people usually drop this like a dogma, and leave the room without further explanation. I've seen this used in so many different places and contexts, that it looks like people can agree on the catchphrase, but they seem to be talking about different things entirely.
So, back to the question: if comments should tell you WHY, what is this WHY we are talking about? Is this the reason why that piece of code exists in the first place? Is this what that piece code should be doing? I would really appreciate if someone could give a clear explanation, and then add some good examples (bad examples are not really needed, but fell free to add them for contrast).
Please do not immediately close this question as duplicate or polemic. I have tried hard to make it very objective. There are many questions on whether comments are good or bad, but no one that addresses the specific question of what are good examples of comments that tell you WHY.
Thanks,
Comments serve two main purposes:
to summarise. Many would say "why document this method when we can just read the code?", but one line of text that describes what a method is for/what it does, can often be much faster to read and easier to understand than 30 lines of code, especially if that code calls other methods that you may need to read as well...
to explain the things that are not obvious from the code - the WHY, or more detail on the how. Simple examples include "we must add the new XmlElement and then remove the old one, as the ReplaceChild method in .net does not work!", or "Uses an iterative Newton-Raphson approach to solve for X ", or "we must not close the port here because the reading thread may still be running", or "use this method where performance is critical, but beware that this method may provide a result that is in error by up to 5%"
Simple question, just no luck on Google.
I was wondering it there is a difference in using
Zend_Controller_Request_Http::setBaseUrl(); and Zend_Controller_Request_Http::setBaseUrl('');
It seemed to me that using Zend_Controller_Request_Http::setBaseUrl('') could be seen as accident prone later on, correct me if I'm wrong.
The end result is the same. Rather than worrying about which one to use, just don't set a base URL if you don't have one.
I see that some programmers add code that, after all, does not do anything useful. For instance (C#):
[Serializable]
class Foo {
// ...
string SerializeMe() {
return new XmlSerializer(typeof(this)).Serialize(this).ToString(); // serialize to xml (syntax wrong, not important here)
}
}
The class is marked as Serializable, but the only way it is serialized is by means of XmlSerialization, which does not require that class attribute at all.
I personally hate this kind of useless code, but I see it quite often and I'm curious as to what others think about it. Is this not so serious a flaw after all? Is it common practice in the industry? Or is this just plain bad and should be removed no matter what?
Good Source Control means that useless code or code that is no longer required should be removed. It can always be retrieved from the source control at a later date.
My rule of thumb,
If its not used get rid of it.
All surplus comments, attrributes are just noise and help your code to become unreadable. If left there they encourage more surplus code in your code base. So remove it.
I try to follow the YAGNI principle, so this bothers me as well.
Does it take even a minimal effort to read that additional (useless, as you added) code?
If yes (and I think it is so) then it should not be in the code. Code like this is polluted with extra snippets that are not useful, they are there "just in case".
The "later on refactoring" of these things can be painful, after 6 o 12 months, who is going to remember if that was really used?
Really don't like it.
Because I then spend valuable time trying to figure out why it's there. Assuming that if it's there, it's there for a reason, and if I don't see the reason, then there's a chance I'm missing something important that I should understand before I start messing with the code. It irritates me when I realize that I've just wasted an hour trying to understand why, or what, some snippet of code is doing, that was just left there by some developer too lazy to go back and remove it.
Useless one-liner code can and should be removed.
Useless code that took time to write can and should be removed...but people in charge tend to get queasy about this. Perhaps the best solution is to have a ProbablyUselessButWhoKnows project where everyone can check in pointless code that might be used again in two or three years. If nothing else, this way people don't have to feel nervous about deleting it.
(Yes, in theory you can get it out of source control, but old deleted code in source control is not exactly highly discoverable.)
In a commercial project - I'd say no, especially if someone can de-assemble it for reading and then has a WTF moment.
In a home-project - sure why not, I often keep some snippets for later use.
Well I can't comment this particular piece of code without knowing your background but I personally follow strictly a rule not to have anything in code unless I really need it. Or at least know that it may be useful some day for something I have in mind already now.
This is bad code.
Bad code is common practice.
That being said sometimes it is not worth the effort in changing stuff that isn't "broken".
It would seem that perfection is attained not when no more can be added, but when no more can be removed. — Antoine de Saint-Exupéry
Is think the meaning of useless is that it cannot and will not be used. I also think that an open door is very open.
If there is an active plan to use this additional feature, then keep it in.
If you know it will never be used, or if that plan stopped being relevant 6 months ago, then pull it out. I'd comment it out first, then remove it fully later.
I'm in the midst of rescoping a lot of variables that were public but really only need to be protected or private, simply because they don't make sense from an API perspective to be exposed--that and nothing uses them.
I edited the question after David Hanak's answer (thanks btw!). He helped with the syntax, but it appears that I wasn't using the right function to begin with.
Basically what I want is to let the compiler ignore multiple definitions of a certain label and just use the first. In order to do that, I thought I'd just do something like this:
\makeatletter
\newcommand{\mylabel}[1]{
\#ifundefined{#1}{\label{#1}}{X}
}
\makeatother
This does not work though, because the first option is always chosen (it doesn't matter if the label is defined or not). I think the \#ifundefined (and the suggested \ifundefined) only work for commands and not for labels, but I don't really know much about LaTeX. Any help with this would be great! Thanks!
Much later update:
I marked David Hanak's response as the correct answer to my question, but it isn't a complete solution, although it really helped me.
The problem is, I think but I'm no specialist, that even though David's code checks to see if a label is defined, it only works when the label was defined in a previous run (i.e. is in the .aux file). If two \mylabels with the same name are defined in the same run, the second will still be defined. Also, even if you manage to work around this, it will make LaTeX use the first label that you defined chronologically, and not necessarily the first in the text.
Anyway, below is my quick and dirty solution. It uses the fact that counters do seem to be defined right away.
\newcommand{\mylabel}[1]{%
\#ifundefined{c##1}{%
\newcounter{#1}%
\setcounter{#1}{0}%
}{}%
\ifthenelse{\value{#1} > 0}{}{%
\label{#1}%
\addtocounter{#1}{1}%
}%
}
I'm not sure if it is necessary to initialize the counter to 0, as it seems like a likely default, but I couldn't find if that was the case, so I'm just being safe.
Also, this uses the 'ifthen' package, which I'm not sure is necessary.
I am also not a LaTeX expert, however after one day of trying and searching the internet the following worked for me. I have used a dummy counter to solve the problem. Hopefully this helps, apparently not many people are looking for this.
\newcommand{\mylabel}[1]{
\ifcsname c##1\endcsname%
\else%
\newcounter{#1}\label{#1}%
\fi%
}
# is a special character in LaTeX. To make your declaration syntactically correct, you'll have to add two more lines:
\makeatletter
\newcommand{\mylabel}[1]{
\#ifundefined{#1}{\label{#1}}{X}
}
\makeatother
The first line turns # into a normal letter, the last line reverses its effect.
Update: You might also want to take a look at the "plain" \ifundefined LaTeX macro.
Update 2
Okay, I did some research to figure out the answer to the real problem. The thing is that defining a label does not create a macro by that name; it prepends a "r#" to it. So try the following:
\makeatletter
\newcommand{\mylabel}[1]{
\#ifundefined{r##1}{\label{#1}}{X}
}
\makeatother
For more technical details, refer to line 3863 of latex.ltx in your LaTeX distribution (where it says \def\newlabel{\#newl#bel r}).
By Victor Eijkhout, "TeX by Topic", p.143:
\def\ifUnDefinedCs#1{\expandafter\ifx\csname#1\endcsname\relax}
This can be used to check whether a label is defined; if not, the label is printed:
\newcommand{\myautoref}[1]{\ifUnDefinedCs{r##1}{\color{magenta}\IDontKnow\{#1\}}\else\autoref{#1}\fi}