Re: Handling input and graphics in a game engine - C / C++ / MFC Discussion Boards

Re: Handling input and graphics in a game engine

Cyrilix18-Jun-07 10:43

18-Jun-07 10:43

There will have to be game animation regardless of user input. When I say "if it sees another command such as the movement keys, then it will draw the next frame", I mean that if it sees that you're holding down the movement key to move in direction x, it will increment an x counter (based on how long you've been holding down the key). The bit of code above that I posted will check this counter every time a frame is drawn (DrawGLScene()) and translate the camera x units from the (0, 0, 0) position (or rather, translate the objects -x, since it's the objects that are moving, and not you). The main point is, it uses a while loop to constantly spit out frames to the screen. I thought you were advocating against using the while loop and producing frames only when you receive a signal, but it seems like you're not against doing so.

We may have misunderstood each other.

Re: Handling input and graphics in a game engine

Force Code18-Jun-07 10:48

Force Code

18-Jun-07 10:48

I have a feeling I may not be completely clear to you.

In the code sample, he has something he feels he has to do continuously. In that instance just create a seperate thread, and do it continously, and let the OS interrupt - No need to call PeekMessage. However, this code doesn't create a seperate thread but is in the main thread, that's why PeekMessage is being used. (You OTOH were saying you wanted to create a seperate thread for graphics updates.) However, in your case, you seemed to say you had nothing to do in the Graphics thread until some user input was received, so you would have a loop to just check for it continuously. That's a complete waste.

Re: Handling input and graphics in a game engine

Cyrilix18-Jun-07 11:18

Cyrilix

18-Jun-07 11:18

The graphics thread always has something to do. It has to draw the frames, whether or not user input is entered. If no user input or no AI interaction (that results in a change of what you can see on the screen) is there, then it should just draw the same frame, and then keep on drawing frames forever after that.

First, I'd like to ask whether or not you're disputing my statement above, because everything I mentioned in the last few posts is in question to whether or not you dispute drawing frames continuously.

Re: Handling input and graphics in a game engine

Force Code18-Jun-07 12:10

Force Code

18-Jun-07 12:10

Cyrilix wrote:
The graphics thread always has something to do. It has to draw the frames, whether or not user input is entered. If no user input or no AI interaction (that results in a change of what you can see on the screen) is there, then it should just draw the same frame, and then keep on drawing frames forever after that.

First, I'd like to ask whether or not you're disputing my statement above, because everything I mentioned in the last few posts is in question to whether or not you dispute drawing frames continuously.

I'm not sure if I dispute it. How do you control at what rate the frames are being updated? If on a given frame, nothing has changed, do you go ahead and redraw it anway? It seems you would only update at set time intervals (1/10 of a second or 1/100, whatever), in which case you could put the update code in the main thread and have it triggered by WM_TIMER messages. Or, if running continuously in a seperate thread, Sleeping for a set time interval on each iteration. Maybe the AI engine could be running continuously in a seperate thread, and when it was time for an update, you could query it, and it could give the best data it had at the moment.

------

I guess I need to read more carefully - you did say a frame is updated whether its changed or not. I would say it should be on a timer.
You did say you were a beginner. I have written a several thousand line long windows app that is fairly entertaining game that is a little more sophisticated than pac-man.

Re: Handling input and graphics in a game engine

Cyrilix18-Jun-07 12:29

Cyrilix

18-Jun-07 12:29

I see what you mean, although I'm unsure of the implementation, but I will look into what you've suggested a bit more before making my decision.

Thanks.

Re: Handling input and graphics in a game engine

Matthew Faithfull18-Jun-07 10:55

Matthew Faithfull

18-Jun-07 10:55

Most games today are single threaded, believe it or not. They work everything on a frame by frame basis so for each frame they render all the graphics, do some user input and sometimes use up the rest of the time until they have to do the next frame by doing some AI or some house keeping operations.
I have tried implementating a properly multithreaded game engine with rendering on one thread, game mechanics on another and yet another for sound. It's HARD to get the kind of performance pro games expect doing it that way. When quad core is standard it will come and my AG engine will rock Big Grin | :-D

Nothing is exactly what it seems but everything with seems can be unpicked.

Re: Handling input and graphics in a game engine

Cyrilix18-Jun-07 11:09

Cyrilix

18-Jun-07 11:09

Hi Matthew,

After all this long discussion, I'm still trying to figure out, regardless of whether I use multiple threads or a single thread, whether or not using a while loop to continuously draw my scene as in the OpenGL example, is the right thing to do.

My fundamental design for single thread is very simple: Do the DrawScene loop and take the input before drawing the frame each time. If there is no input or no AI interaction, then it will just draw the same scene as it did last time.

My fundamental design for multiple threads is just as simple: Do the input loop in the input thread, do the DrawScene loop in the graphics thread, and have the DrawScene take the input before drawing the frame every time. If there is no input or no AI interaction, then it will just draw the same scene as it did last time.

Re: Handling input and graphics in a game engine

Matthew Faithfull18-Jun-07 13:03

Matthew Faithfull

18-Jun-07 13:03

Your method should work fine for single threaded. When I was experimenting with this I was using DirectX 8 and that has a setting which redraws the actual screen exactly 60 times a second. I used this mode so I did the frames based on a timer. No point in drawing 2 frames in 1/60th of a second if the display will only show 1 Smile | :)

. Something like this

<br />
while( !bFinished )<br />
{<br />
DWORD dwTickCount = GetTickCount();<br />
RenderFrame();<br />
if( GetTickCount() - dwTickCount < 1000/120 )//we've got loads of time<br />
{<br />
  //do some other stuff<br />
}<br />
<br />
while( GetTickCount() - dwTickCount < 1000/60 )<br />
{<br />
  //Process some user input<br />
}<br />
<br />
}<br />

For a real system you'd probably want to use a high resolution timer.

Multithreaded is much more difficult becuase you need the rendering thread to be on a higher priority so it doesn't get interrupted by every user input. Once it's on a higher priority then it tends to hog almost all the run time. As I said to make it work smoothly you'd need Dual Core or multiple processors. The best I managed was to get a very choppy approximation of 60 FPS for <1000 polygons, while playing a tune and taking simple keyboard input. Not spectaclar even 3 years ago. Laugh | :laugh:

I used a class representing the game state which was shared data for all the threads. Each thread had a set of functions it called within any state, like Render or CalculateMoves or PlaySample. By tuning each state with delays or synchronisation it could roughly be made to work. Communication between the threads was by means of a subsciber queue. The states were kept on a stack which worked well for a game type situtation. If I ever get a Dual Core PC maybe I'll ressurect it and post it on CP Big Grin | :-D

Nothing is exactly what it seems but everything with seems can be unpicked.

Multiple bitmap in VMR9

houari_id18-Jun-07 7:30

houari_id

18-Jun-07 7:30

Hi all...

Is it possible to mix more than one bitmap in VMR9 using MixerBitmap in one time? I've tried to create two IVMRMixerBitmap instances, two SetInitialAlphaBitmap functions (as in BmpMix9 example), but only the last one is displayed.

Thank you...

-Houari

Re: Multiple bitmap in VMR9

Mark Salsbery18-Jun-07 7:45

Mark Salsbery

18-Jun-07 7:45

IVMRMixerBitmap::SetAlphaBitmap() sets a new bitmap, replacing the previous one.

You can, however, combine your bitmaps into one bitmap Smile | :)

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

Re: Multiple bitmap in VMR9

houari_id18-Jun-07 8:00

houari_id

18-Jun-07 8:00

ah yes... that was in my mind too... ^^
but I need the position of my bitmaps in the video to be independently changed anytime I want.

is there any way to do this? I was also failed by using CDC in the same picture control with the vmr video (the CDC drawing is overlapped by the video...) -_-

thanks

-Houari

Re: Multiple bitmap in VMR9

Mark Salsbery18-Jun-07 8:47

Mark Salsbery

18-Jun-07 8:47

houari_id wrote:
but I need the position of my bitmaps in the video to be independently changed anytime I want.

You'd need to redraw the offscreen bitmap each time the bitmaps change position.

If you're experienced with DirectDraw (I personally am not) you can also use the
VMR Renderless Playback Mode (Custom Allocator-Presenters)[^].

The alternative I chose was to make my own renderer filter so I had complete control over all the
drawing. That certanly isn't a necessary solution however.

houari_id wrote:
I was also failed by using CDC in the same picture control with the vmr video (the CDC drawing is overlapped by the video...)

Yeah, that won't work well.. That's why mixing is necessary Smile | :)

Mark

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

C++ Program with date and class

berni2k18-Jun-07 6:41

berni2k

18-Jun-07 6:41

Hi,

How could i code this fast in C++ by using classes:
I want to output the work days between two dates (start and end date input by user).

I thought through it but dont know how to code it.

My thoughts:
1) calculate (count up) the absolute days between the two dates (with using time.h and week modulo to find out the free Sundays)
2) make a class with holidays
3) calculate the holidays with the Gauss easter algorithm (found it on wikipedia and some other site, see bottom of post)
4) substract the holidays from the absolute days
5) "cout" the absolute days and the count up of holidays and the final work days

Carl Friedrich Gauß (1777 - 1854):

a = YYYY mod 19
b = YYYY mod 4
c = YYYY mod 7
d = (19a + M) mod 30
e = (2b + 4c + 6d + N) mod 7

YYYY: the year with 4 digits

M and N:
for 1583 - 1599 -> M=22, N=2
1600 - 1699 -> 22, 2
1700 - 1799 -> 23, 3
1800 - 1899 -> 23, 4
1900 - 1999 -> 24, 5
2000 - 2099 -> 24, 5
2100 - 2199 -> 24, 6
2200 - 2299 -> 25, 0
2300 - 2399 -> 26, 1
2400 - 2499 -> 25, 1

taking the above easter sunday should be: (22 + d + e).March or (d + e - 9).April
and there are 2 annomalies:
1) if the result of the above falls on the 26th of April -> easter sunday will be held on the 19th of April instead
2) If a > 10 and d = 28 and the result the 25. April, -> easter sunday be corrected to the 18. April.

but how to code this?
HELP

thx a lot

berni2k

Re: C++ Program with date and class

led mike18-Jun-07 7:10

led mike

18-Jun-07 7:10

berni2k wrote:
but how to code this?

Indeed. That sound like a very interesting class assignment. Good luck.

Re: C++ Program with date and class

berni2k18-Jun-07 8:36

berni2k

18-Jun-07 8:36

thx, I am on the way and will post the code if i can manage to do it

stack overflow

Lord_Vader18-Jun-07 6:26

Lord_Vader

18-Jun-07 6:26

Hello, I have two questions about the stack.

1st)In MS visual studio the stack is 1MB as far as I now.
I found that using a recursive function the stack overflows at depth ~4900.
Why does this happen?

2nd)If someone has a linked list with thousand of elements how he can
reach the whole list using a recursive function?

thanks.

Re: stack overflow

led mike18-Jun-07 6:39

led mike

18-Jun-07 6:39

Lord_Vader wrote:
1st)In MS visual studio the stack is 1MB as far as I now.

Lord_Vader wrote:
Why does this happen?

When you reach the limit, regardless of what that is, you get the overflow error. What is so hard to understand about that?

Lord_Vader wrote:
2nd)If someone has a linked list with thousand of elements how he can
reach the whole list using a recursive function?

Why would you want to do that?

Re: stack overflow

Lord_Vader18-Jun-07 6:44

Lord_Vader

18-Jun-07 6:44

1st)Its not hard to understand that.
But I want someone to explain specifically what happens, for example how much stack
memory one function call consumes why...

2nd)Because I have a linked list with thousand elements and I wondering if it is
possible to go through it using recursive functions.

Re: stack overflow

Cyrilix18-Jun-07 6:46

Cyrilix

18-Jun-07 6:46

Why would you iterate through a linked list with a recursive function? You already figured out the answer to your question: it is not possible unless you increase the stack size, since you seem to top at around 4900.

Just call the next pointer until you reach the end of the list. It only takes a single function.

Re: stack overflow

Lord_Vader18-Jun-07 6:52

Lord_Vader

18-Jun-07 6:52

Ok thanks,I was going to do that,
but I posted mainly to learn the details behind a functions call..

Re: stack overflow

James R. Twine18-Jun-07 7:14

James R. Twine

18-Jun-07 7:14

   Stack memory is generally required for the function call information (return values and return address), as well as for the automatic variables in the function being called. One function may consume only 32 bytes of stack while another consumes more than 8KB of stack.

   It is possible to recursively iterate over any size list... Given you have enough stack space and your environment supports it. Realistically, this depends on (1) how much stack is consumed by the recursive function, (2) how many elements are in the list, and (3) how much free stack space you have remaining at the time you start recursion (just because you have 1MB of stack by default in Win32, that does not mean that by the time your function is first called that you will have much of it left).

   Iteration is generally better done using loops instead of recursion. It is also easier to debug, because you can more easily break at a certain loop counter than a certain recursion depth.

   Peace!

-=- James
Please rate this message - let me know if I helped or not!<HR>If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
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Re: stack overflow

Lord_Vader18-Jun-07 7:58

Lord_Vader

18-Jun-07 7:58

Thanks,
Here is another one.
I additionally have a bin tree with many thousands of elements.
I use recursive functions to walk through the leafs because its more intuitive.
Will it be faster if I use loops instead?

Re: stack overflow

James R. Twine18-Jun-07 11:37

James R. Twine

18-Jun-07 11:37

   It may be faster to use loops, depending on the setup required for the recursive function call (stack frame setup, construction/destruction of any local objects, exception handling setup if used, etc.). If your function uses poor coding habits, like using a CString instead of a local buffer for simple formatting, using the loop will very likely be faster than recursion, because you can eliminate the overhead of allocating/deallocating the memory for the string. (You may not notice a difference when only calling the function 100 or so times, but when you start hitting the 1000+ ranges, you may.)

   A (well-balanced) binary tree is likely to have less recursive demand, whereas a list is a linear structure so your recursion level would be equal to the number of items in the list. Trees tend to have less depth when used/populated correctly.

   Peace!

Re: stack overflow

Lord_Vader19-Jun-07 5:38

Lord_Vader

19-Jun-07 5:38

Thanks,Specifically I am working on a graphics algorithm which uses a binary tree
to draw triangles(which are the leafs) on the screen. Now if you consider that I would
like to have ~60000 leafs displayed every frame using a recursive function,
this is quite cumbersome.Additionally the tree may not be so balanced, but the maximum
depth of the tree wont be larger than ~14.Thats why I asked.

Re: stack overflow

#realJSOP19-Jun-07 3:41

#realJSOP

19-Jun-07 3:41

Each function call in a recursive loop consumes stack space. If you're passing parameters, that consumes even more stack space. I thought the max stack space for a given app was limited to 64k...

Of course, I'm old, so it may have changed since I last checked it out. Smile | :)

"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
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