I'm making a console game called alien spaceships as a homework. It should look something like this http://img74.imageshack.us/img74/8362/alieninvadersfdcl192720mu1.jpg .
So far so good I ain't allowed to use classes nor objects => only functions and arrays.
I have one while loop that checks the buttons I press on the keyboard and according to the button applies some functions.
The problem comes when I try to shoot a missle because it's done with a "for" loop and when I shoot I can't move. Can someone give me an idea how the model is supposed to look like and how can I make something like this work. I don't think it's needed to post my code, but if you want I'll post it.
I assume that you're not willing to play with multiple threads. It is not mandatory for a simple game like this and would add a bit of complexity.
So generic loop for monothreaded game is:
state new_state = createInitialState();
do
{
input = readInput(); // non blocking !
new_state = modifyState(input, new_state);
updateScreen(new_state);
}
while (!exitCondition(input));
None of these functions should loop for long.
In your case, the missile position should be updated in modifyState taking into account the time since the last modifyState.
I assume you use a matrix to store all the data, and periodically you print the content of the matrix (that's how you create a console game).
So, your code should look something like this:
render()
{
update_position(x,y);
if(missile_fired)
update_missile_position();
}
main()
{
for(;;)
{
read_input(&x,&y);
render();
draw_image();
}
}
Related
I'm not much of a C++ programmer, and I'm looking for help with implementing Steam Input into my Unreal Engine 3 game (yes, that's 3 and not 4). I'm under NDAs to both Epic (for Unreal 3) and Valve (for Steamworks), so I don't think I'm able to copy any of their code, but I'm going to do my best here to describe what's going on. And if you know of a better place I can ask these questions, please let me know. And if you think I'm violating an NDA, please let me know that too so I can delete the offending portions.
I have a UE3 game that works with mouse and keyboard. Steam Input, which is part of the Steamworks SDK, provides a way to get input from any controller. Basically, your controller, your actions (such as "shoot" or "walk forward"), and action sets (control schemes that can change based on game state, such as "in menu," "walking," or "driving") all get assigned unique UINT64 handles. I'm at the stage where I'm using the provided functions to assign handles, and it's crashing my game.
I have a class that contains these variables...
// typedef uint64 InputActionSetHandle_t;
InputActionSetHandle_t IsometricSetHandle;
InputActionSetHandle_t WorldMapSetHandle;
InputActionSetHandle_t SquadMenuSetHandle;
InputActionSetHandle_t BattleSetupSetHandle;
InputActionSetHandle_t InBattleSetHandle;
InputActionSetHandle_t MenuSetHandle;
I create an object and then I try to set up its variables by calling this function.
void URPGTacSteamInput::SetActionSetHandles()
{
IsometricSetHandle = SteamInput()->GetActionSetHandle( "Isometric" );
WorldMapSetHandle = SteamInput()->GetActionSetHandle( "WorldMap" );
SquadMenuSetHandle = SteamInput()->GetActionSetHandle( "SquadMenu" );
BattleSetupSetHandle = SteamInput()->GetActionSetHandle( "BattleSetup" );
InBattleSetHandle = SteamInput()->GetActionSetHandle( "InBattle" );
MenuSetHandle = SteamInput()->GetActionSetHandle( "Menu" );
}
The function completes, but the game crashes later, with the error "Unhandled exception ... Access violation reading location ..." Call stack location is FArchiveRealtimeGC::PerformReachabilityAnalysis(), which I understand is part of Unreal 3's garbage collection system.
I'm not sure how to tackle this problem, and I've just been trying stuff. I logged the handles that get assigned, and I tried setting those handles manually:
void URPGTacSteamInput::SetActionSetHandles()
{
IsometricSetHandle = 1;
WorldMapSetHandle = 2;
SquadMenuSetHandle = 3;
BattleSetupSetHandle = 4;
InBattleSetHandle = 5;
MenuSetHandle = 6;
}
But the game still crashes after running that function. So I tried removing more from it.
void URPGTacSteamInput::SetActionSetHandles()
{
}
And I can run that function, and the game moves along just fine, except that I don't have any Steam Input action sets I can switch to.
So what might I be able to check to find out why my game is crashing? What else would I need to find out in order to track this down? Is there somewhere else I might have better luck asking about this issue?
Thanks for any guidance you can give me on this.
I found the problem. I was declaring all of my InputActionSetHandle_t variables in the cpptext area of my UnrealScript classes. I'm not supposed to do that. I declared all of those variables as UnrealScript qwords instead, and they work just fine for holding the C++ uint64 handles that get sent back by the Steam API. And no more crashes.
Ok I am trying to switch my Game Engine to multithreading. I have done the research on how to make it work to use OpenGL in multithreaded application. I have no problem with rendering or switching contexts. Let my piece of code explain the problem :) :
for (it = (*mIt).Renderables.begin(); it != (*mIt).Renderables.end(); it++)
{
//Set State Modeling matrix
CORE_RENDERER->state.ModelMatrix = (*it).matrix;
CORE_RENDERER->state.ActiveSubmesh = (*it).submesh;
//Internal Model Uniforms
THREAD_POOL->service.post([&]
{
for (unsigned int i = 0; i < CORE_RENDERER->state.ActiveShaderProgram->InternalModelUniforms.size(); i++)
{
CORE_RENDERER->state.ActiveShaderProgram->InternalModelUniforms[i]->Set( CORE_RENDERER->state.ModelMatrix);
}
CORE_RENDERER->state.ActiveSubmesh->_Render();
});
//Sleep(10);
}
I'll quickly explain what are the elements in the code to make my problem more clear. Renderables is a simple std::vector of elements with _Render() function which works perfectly. CORE_RENDERER->state is a struct holding information about current render state such as current material properties as well as current submesh ModelMatrix. So Matrix and Submesh are stored to state struct (I KNOW THIS IS SLOW, I'll probably change that in time :) ) The next piece of code is sent to THREAD_POOL->service which is actually boost::asio::io_service and has only one thread so it acts like a queue of rendering commands. The idea is that the main thread provides information about what to render and do frustum culling and other tests while an auxilary thread does actual rendering. This works fine, except there is a slight problem:
The code that is sent to thread pool starts to execute, but before all InternalModelUniforms are set and submesh is rendered the next iteration of Renderables is executed and both ModelMatrix and ActiveSubmesh are changed. The program doesn't crash but both informations change and some meshes are rendered some matrices are right others not which results in flickering image. Objects apear on frame and the next frame they are gone. The problem is only fixed if I enable that Sleep(10) function which makes sure that the code is executed before next iteration which obviously kills the idea of gaining preformance. What is the best possible solution for this? How can I send commands to the queue each with unique built in data? Maybe I need to implement my own queue for commands and a single thread without io_service?
I will continue my research as I know there is a way. The idea is right cause I get preformance boost as not a single if/else statement is processed by the rendering thread :) Any help or tips will really help!
Thanks!
Update:
After struggling for few nights I have created a very primitive model of communication between main thread and an Aux Thread. I created a class that represents a base command to be executed by aux thread:
class _ThreadCommand
{
public:
_ThreadCommand() {}
~_ThreadCommand() {}
virtual void _Execute() = 0;
virtual _ThreadCommand* Clone() = 0;
};
These commands that are childs of this class have _Execute() function to do whatever operation needs to be done. The main thread upon rendering fills a boost::ptr_vector of these commands While aux thread keeps on checking if there are any commands to process. When commands are found it copies entire vector to it's own vector inside _AuxThread and clears the original one. Commands are then executed by calling _Execute functions on each:
void _AuxThread()
{
//List of Thread commands
boost::ptr_vector<_ThreadCommand> _cmd;
//Infinitive loop
while(CORE_ENGINE->isRunning())
{
boost::lock_guard<boost::mutex> _lock(_auxMutex);
if (CORE_ENGINE->_ThreadCommands.size() > 0)
{
boost::lock_guard<boost::mutex> _auxLock(_cmdMutex);
for (unsigned int i = 0; i < CORE_ENGINE->_ThreadCommands.size(); i++)
{
_cmd.push_back(CORE_ENGINE->_ThreadCommands[i].Clone());
}
//Clear commands
CORE_ENGINE->_ThreadCommands.clear();
//Execute Commands
for (unsigned int i = 0; i < _cmd.size(); i++)
{
//Execute
_cmd[i]._Execute();
}
//Empty _cmd
_cmd.clear();
}
}
//Notify main thread that we have finished
CORE_ENGINE->_ShutdownCondition->notify_one();
}
I know that this is a really bad way to do it. Preformance is quite slower which I'm quite sure is because of all the copying and mutex locks. But at least the renderer works. You can get the idea of what I want to achieve but as I said I am very new to multithreading. What is the best solution for this scenario? Should I return back to ThreadPool system with asio::io_service? How can I feed commands to AuxThread with all values that must be sent to renderer to preform tasks in correct way?
First, a warning. Your "slight problem" is not slight at all. It is race condition, which is undefined behavior in C++, which, in turn, implies that anything could happen, including:
Everything renders fine
Image flickers
Nothing renders at all
It crashes on the last Saturday of every month. Or working fine on your computer and crashing on everyone's else.
Seriously, do not ever rely on UB, especially when writing library/framework/game engine.
Now about your question.
Lets leave aside any practical benefits of your approach and fix it first.
Actually, OpenGL implementation uses something very similar under the hood. Commands are executed asynchronously by the driver thread. I recommend you to read about their implementation to get some ideas on how to improve your design.
What you need to do, is to somehow "capture" the state at the time you post a rendering command. Simplest possible thing - copy the CORE_RENDERER->state into closure and use this copy to do the rendering. If state is large enough, it can be costly, though.
Alternative solution (and OpenGL goes that way) is to make every change in the state a command also, so
CORE_RENDERER->state.ModelMatrix = (*it).matrix;
CORE_RENDERER->state.ActiveSubmesh = (*it).submesh;
translates into
Matrix matrix = (*it).matrix;
Submesh submesh = (*it).submesh;
THREAD_POOL->service.post([&,matrix,submesh]{
CORE_RENDERER->state.ModelMatrix = matrix;
CORE_RENDERER->state.ActiveSubmesh = submesh;
});
Notice, however, that now you can't simply read CORE_RENDERER->state.ModelMatrix from your main thread, as it is changing in a different thread. You must first ensure that command queue is empty.
I'm writting a game using C++. I wonder how can I optimize my game loop. For example, we have some game with the main loop looks like this:
while ( gameContinue ) {
if ( SCENE == HELP_SCENE ) {
renderHelpScene();
} else if ( SCENE == SCORE_SCENE ) {
renderScoreScene();
} else if ( SCENE == MAIN_GAME_SCENE ) {
renderMainGameScene();
} // .... and many others scenes
}
I'm thinking on how to make this code faster and lighter. I think about using callbacks so we will not need many if-cases. Something like this:
typedef void (*callback_function)(void);
callback_function renderFunc;
void renderMainGameScene() {
renderFunc = renderScoreScene(); // set to another scene if we need this
}
void renderScoreScene() {
renderFunc = renderAnyAnotherSceneWeNeedNow();
}
renderFunc = renderMainGameScene();
while ( gameContinue ) {
renderFunc();
}
What do you think about it? How do you organize your main loops?
I've personally started using multi-threading. I have a thread for object updates, a thread for objects collision and a thread for drawing. Each thread loops with a while (GetMessage()) and threads send messages from one to another.
At each cycle (frame), my main loop sends a message to each thread to:
Calculate collision for modified objects
Update objects (movement, state etc.)
Draw the updated objects
That's how I do it (at least on my GDI/GDI+ games). Not sure if the best way, but so far it works like a charm :).
Helpful patterns for this kind of problem are the State Pattern and the Strategy Pattern.
As you can see they are both similar. The Strategy pattern is a bit simpler than the State, but in exchange the State Pattern is more powerful and probably better fitted for a game engine like this. You can also easily create a stack with this for example: game start -> menu -> game run -> menu.
If the parent state of the last menu is game run, the menu would look different (e.g. "Return game" instead of "Start game" in the first menu). The states can be popped and you have a easy navigation.
Using call-backs should be fine. Just be careful not to have any cyclic dependencies in your headers. Notably it's a bad idea to include the header for your controller loop anywhere other than the .cpp for the controller loop.
As for the runtime benefits, they are very small. The if-else method will not noticeably slow down your game. Alternatively, there is also the switch statement, which is preferable to a series of if-else statements in terms of code readability.
I'm porting a game from Ruby to C++. There is a main render loop that updates and draw the content. Now let's say that during the game, you want to select an item another screen. The way it's done in the original code is to do Item item = getItemFromMenu(); getItemFromMenu is a function that will open the menu and do have its own update/render loop, which mean that during the whole time the player has this other screen open, you are in a nested render loop. I feel like this is a bad method but I'm not sure why. On the other hand it's very handy because I can open the menu with just 1 function call and so the code is localized.
Any idea if this is a bad design or not?
I hesitated to post it on gamedev, but since this is mostly a design issue I posted it here
edit : some pseudo-code to give you an idea:
The usual loop in the main part of the code:
while(open) {
UpdateGame();
DrawGame();
}
now inside UpdateGame() i would do something like:
if(keyPressed == "I") {
Item& item = getItemFromInventory();
}
And getItemFromInventory():
while(true) {
UpdateInventory();
if(item_selected) return item;
DrawInventory();
}
A good way to handle something like this would be to replace the DrawInventory() call with something like InvalidateInventory(), which will mark the current graphical state of the inventory as outdated and request it to be redrawn during the next frame rendering (which'll happen pretty soon after when the main loop gets to DrawGame()).
This way, you can keep running through the main loop, but the only parts of the screen that get looked at for redrawing are the ones that have been invalidated, and during normal gameplay you can invalidate your (2/3)D environment as a normal part of processing, but then inside the inventory you can always mark only inventory assets as needing to be redrawn, which minimises overhead.
The other part of your inner loop, UpdateInventory(), can be a part of UpdateGame() if you use a flag to indicate the current game state, something like:
UpdateGame()
{
switch(gameState)
{
case INVENTORY:
UpdateInventory();
break;
case MAIN:
default:
UpdateMain();
break;
}
}
If you really wanted, you could also apply this to drawing:
DrawGame()
{
switch(gameState)
{
case INVENTORY:
DrawInventory();
break;
case MAIN:
default:
DrawMain();
break;
}
}
But I think drawing should be encapsulated and you should tell it which part of the screen, rather than which separate area of the game, needs to be drawn.
What you've created with your nested render loop is functionally a state machine (as most game render loops tend to be). The problem with the nested loop is that many times you'll want to do the same sorts of things in your nested loop as your outer loop (process input, handle IO, update debug info etc).
I've found that it's better to have one render loop and use a finite state machine (FSM) to represent your actual states. Your states might look like:
Main menu state
Options menu state
Inventory state
World view state
You hook up transitions between states to move between them. The player clicking a button might trigger the transition which could play an animation or otherwise, then move to the new state. With a FSM your loop might look like:
while (!LeaveGame()) {
input = GetInput();
timeInfo = GetTimeInfo();
StateMachine.UpdateCurrentState(input, timeInfo);
StateMachine.Draw();
}
A full FSM can be a bit heavyweight for a small game so you can try a simplified state machine using a stack of game states. Every time the user does an action to transition to a new state you push the state on a stack. Likewise when they leave a state you pop it off. Only the top of the stack typically receives input and the other items on the stack may/may not draw (depending on your preference). This is a common approach and has some upsides and downsides depending on who you talk to.
The simplest option of all is to just throw a switch statement in to pick which render function to use (similar to darvids0n's answer). If you're writing an arcade clone or a small puzzle game that would do just fine.
I am writing a game and am trying to make a person move with the arrow keys.
I have this code
if (Key_Down(DIK_DOWN))
{movedown(player)}
This works but as I want the player to take four steps every time the key is pressed I created and animation loop. so the player cannot input any more move commands until the animation is over and they have taken four steps I made the code this.
if(player.move == false)
{
if (Key_Down(DIK_DOWN))
{movedown(player)}
}
The problem is that now once a button is pressed the program acts like the button is held down and the player keeps moving until another direction is pressed.
Can anyone explain what the outer loop has done to the code and fix the problem ?
it is programmed in visual c++ 2005 and direct x 9.c
Edit:
If I remove the outer loop then the button press is only registered once so I don't think it is the movedown function.
Simply keep track of the keystate in a variable. So you can reset a move counter. Something like this, combining both:
int MovingDown = 0;
...
if (!Key_Down(DIK_DOWN)) MovingDown = 0;
else if (MovingDown < 4) {
MovingDown++;
movedown(player);
}
Hard to tell without seeing more of your codebase but I would guess that you're not re-setting player.move after you've moved the player. Have you tried sticking some break poins in there to see what is being called and why?
If you remove the if(player.move == false) line does it have the same issue? ..or have you changed something elsewhere? If you could post more of your codebase like the whole movedown function and anythnig else which interacts (e.g. the animation code) it would help us help you...
[Edit] Is movedown a macro? Maybe you've got some peculiar side effect eminating from that? If not, it ought to have a semi colon after the function call.
What does KEY_DOWN return? Is that an API call? Try testing against the exact value you expect it to return?