I'm making an Arkanoid clone. This is the program layout I came up with:
source.cpp // few lines
App class // has constants APP_WIDTH and APP_HEIGHT
Ball class // has constant RADIUS
Brick class
Paddle class
Now I want to place the ball at the center of the window at the beginning of the game. Normally I would accomplish it like this:
Ball::Ball (App &app)
{
circle.setPos(app->WINDOW_WIDTH/2-RADIUS/2,app->WINDOW_HEIGHT/2-RADIUS/2)
}
But the ball class doesn't know anything about the App!
Do I need to make APP_WIDTH and APP_HEIGHT global variables?
Or do I need to turn the current app layout upside down, so that Ball class has #include "app.hpp" statement?
EDIT: Or do I need to declare ball, brick and paddle classes inside the app class? But then where I define them? Inside the same app class? Then the header gets too big!
And maybe there are some good tutorials on program layout topic on the internet? I haven't found any...
QUESTION 2:
Why do classes need protected variables if "there is no reason that ball would know anything about app class"
Since the issue seems to be that "Ball doesn't have any access to the private members of app class.", than maybe you want to make a getter.
A getter is a public method that returns the value of a private field.
If you do that, you can access the values of those members like so
circle.setPos(app->GetWidth()....
Your getter might look similar to the following
public int GetWidth()
{
return this.APP_WIDTH;
}
There is no reason for the game objects to know anything about the App they are part of. When it needs any information from App, it should receive them from App directly. This can happen either through setter-methods (recommended when properties can be changed by the App later, like the position of the ball) or in the constructor (recommended for things which don't change, like the positions of blocks).
Ball should have a SetPosition(x,y) which app invokes with the above calculation. Internally, this SetPosition would set the circle like above, so ball knows nothing about app.
Related
I'm trying to figure out the best (cleanest) way to structure some code in C++ for an application I'm building. I think MVC makes sense as the way to go, but after a fair amount of research I'm not totally clear I'm doing things the right way.
Here's an example to illustrate my question:
Model
I have a class which contains drawing data called Canvas. An example function, used to clear the current contents of the canvas, is ClearCanvas().
Ultimately, I want a button in the interface to be able to call this function and clear the canvas.
Controller
I have a controller class for the canvas: CanvasController
The controller creates and then holds a reference to a canvas object: CurrentCanvas
The controller also creates the view: CanvasView and then sets a reference to itself on the view: CurrentCanvasView->SetControllerRef(this);
View
The view is made up of a series of nested classes that define the UI. For example, the hierarchy leading to the button in question might be something like this:
CanvasView
-VerticalBox
--HorizontalBox
---Button
During the view's constructor, a reference to the controller is passed from the view to all interactive elements, eg. NewButton->SetControllerRef(this->GetControllerRef());
Button Pressed
So now when the button is pressed, it can function like this:
void ClearCanvasButton::OnButtonPressed()
{
Controller->CurrentCanvas->ClearCanvas();
}
So my general question is: (1) does this seem like the right way to be doing things, or badly structured?
Also (2): Should the controller be encapsulating the canvas functions, for example:
void CanvasController::ClearCanvas()
{
CurrentCanvas->ClearCanvas();
}
Such that the function on the button could simply be:
void ClearCanvasButton::OnButtonPressed()
{
Controller->ClearCanvas();
}
I'm just not sure whether it's correct to essentially be passing down a reference to the controller to all elements of the view which ultimately want to change the model, or whether there is a cleaner way.
Apologies if the question has been asked a thousand times in a thousand different ways, I have been searching around trying to understand this.
You don't need a class ClearCanvasButton, if your Button class contains a member like
std::function<void()> onButtonPressed;
or similar, rather than
virtual void onButtonPressed() {};
You then pass a lambda that references the controller
CanvasView::CanvasView()
{
// make the widgets
Button.onButtonPressed = [Controller](){ Controller->ClearCanvas(); };
}
I am working on a game in box2d. I have the following code:
for (int contact_num = 0; contact_num<contact_count; ++contact_num)
{
if (contact->IsTouching())
{
// get the colliding bodies
b2Body* bodyA = contact->GetFixtureA()->GetBody();
b2Body* bodyB = contact->GetFixtureB()->GetBody();
// check if one of the colliding objects is a censor
bool sensorA = contact->GetFixtureA()->IsSensor();
bool sensorB = contact->GetFixtureB()->IsSensor();
// do stuff, mainly handling variables
}
}
// Get next contact point
contact = contact->GetNext();
}
All of this is being called in the update function of my main class (which also contains most of the games variables). The problem is that I want the code to only be called when the two objects first collide, because otherwise something like score++ will end up skyrocketing in value as it gets updated for the collisions duration. I am aware of a "contact listener" class in box2d with the function "begin contact", but there is no good documentation that could help a beginer learn how to implement it. For example, if I add a contact listener to my main class, how do I get it to handle my score, for example, if the contact listener doesn't have access to those variables? Or where do I call "begin contact" in the first place? Sorry if these are obvious questions, but i was hoping someone could clarify these. Thank you in advance.
Here's a couple suggestions which hopefully will answer your question:
Take a look at Box2D C++ tutorials - Collision callbacks. Personally, I think it's a great tutorial on using the b2ContactListener class.
Just make your class which contains the score information inherit from b2ContactListener. That way your BeginContact method will have direct access to the score data. Presumably that'll be your "main" class. Be sure to also notify your b2World instance to use this by calling your world instance's SetContactListener method with a pointer to the score containing instance (that you'd subclassed from b2ContactListener).
If you still need more help with this, please add a comment to that effect or update your question to reflect what remains unclear.
The application that I'm building is supposed to create, destroy, and manipluate widgets that I've created
The problem is I'm not making a simple program with nice buttons where everything is symmetrical and needs to be evenly spaced and handled via a layout that will automatically move everything around and space it.
And yet, the only way I know of is to manually instance a layout and add the widgets to it, but then I can't set the coordinates of them
How can I simply instance my widget, and add it to the project generated frame?
This is how I'm instantiating my class, in which case I then set my own parameters:
Tile *tile = new Tile;
tile->setImg("://Images/placeholderTile.png");
tile->setCol(true);
tile->setGeometry(retX(line),retY(line),50,50);
To reiterate, I want to add my own widgets to a frame outside of the editor (only by code), and be able to manually move them around the frame by code.
I don't see an ".addWidget() as a method accessible from the QFrame, and yet they can be children within the designer, why can't I do this by code? Whenever I try to do it manually and add them to any layout, any attempt I make to manually set the widgets location doesn't do anything. I haven't overridden the setGeometry
I fixed my problem
After 2 hours of continual searching I finally came across my answer
I never thought that you could set the parent of a widget by code, as I thought you strictly had to add it in as a child of something else, not the reverse and declare that it should have a parent
So, by simply adding the line:
tile->setParent(ui->frame);
completely fixed my problem.
I will change this post back and submit the answer tomorrow when I'm allowed to by this site.
Thank you to those who actually came though. I'm just glad I managed to fix it before that.
All you need is to pass the parent to the widget's constructor:
Tile *tile = new Tile(ui->frame); // <-- here
tile->setImg("://Images/placeholderTile.png");
tile->setCol(true);
tile->setGeometry(retX(line),retY(line),50,50);
Since Tile is your own class, you should definitely have a Qt-style, parent-taking explicit constructor for it:
class Tile : public QWidget {
...
public:
explicit Tile(QWidget * parent = 0) : QWidget(parent) { ... }
};
Another approach is to write your own layout that would know about the relationships that are to be held between your objects. After you do it once, writing custom layouts isn't that hard.
I recently met a strange problem of my little program and it would be great if you help me to get the reason of this behavior.
My task is quiet simple - I want to use Qt Graphics Framework to show some objects and I want Box2D to calculate bodies position. So my class hierarchy looks like the following:
I have 1 base abstract class B2DObject. It contains some Box2D staff + some common parameters for its successors (names, some flags, etc.). It also has couple of pure virtual functions that will be reimplemented in successor classes.
Then I implement some classes that represent basic shapes: circles, rectangles, polygons, etc. I am doing it in the following way:
class ExtendedPolygon : public B2DObject, public QGraphicsPolygonItem { ... };
class ExtendedCircle : public B2DObject, public QGraphicsEllipseItem { ... };
etc.
(for those who are not familiar with Qt, QGraphics***Item is inherited from QGraphicsItem).
Also I inherited QGraphicsScene and reimplemented its mousePressEvent. In this function I request an object placed at some point on the screen using QGraphicsScene::itemAt function (which returns QGraphicsItem*), convert it to B2DObject* and try to get some internal field from this object:
void TestScene::mousePressEvent (QGraphicsSceneMouseEvent *event)
{
QGraphicsItem* item = itemAt (event->scenePos ());
if (item)
{
B2DObject* obj = reinterpret_cast < B2DObject* > (item);
QString objName = obj->Name(); // just for example,
// getting other internal fields has
// the same effect (described below)
// use retrieved field somehow (e.g. print in the screen)
}
// give the event to the ancestor
}
Unfortunately, dynamic_cast will not work here because these classes are completely unrelated.
Then I create necessary objects and add it to my scene:
ExtendedPolygon* polygon = new ExtendedPolygon (parameters);
polygon->setName (QString ("Object 1"));
...
TestScene scene;
scene.addItem (polygon);
(for those who are not familiar with Qt, here is the prototype of the last function:
void QGraphicsScene::addItem(QGraphicsItem *item);
I guess it just stores all items in internal index storage and calls QGraphicsItem::paint (...) when item needs to be repainted. I suppose QGraphicsScene doesn't make any significant changes to this item).
So my problems start when I run the program and click on an item on the screen. TestScene::mousePressEvent is called (see a piece of code above).
Mouse click position is retrieved, item is found. Casting works fine: in the debugger window (I'm using Qt Creator) I see that obj points to ExtendedPolygon (address is the same as when I add the item to the scene and in the debugger window I can see all the fields). But when I get some field, I receive garbage in any case (and it does not matter, what I'm trying to get - a QString or a pointer to some other structure).
So first of all, I would like to get any advice about my multiple inheritance. In 95% of cases I try to avoid it, but here it is very effective in the programming point of view. So I would appreciate it if you provide me with your point of view about the architecture of the classes hierarchy - does it even suppose to work as I expect it?
If on this level everything is quite fine, then it would be great if someone gets any idea why doesn't it work.
I have some ideas about workaround, but I really would like to solve this problem (just in order not to repeat the same error anymore).
Looks like I've found the root cause of my problem. It was just lack of knowledge regarding how multiple inheritance really works on data layer.
Let's assume that we have 2 basic classes, A and B. Each of them provides some internal data fields and some interfaces.
Then we create a derived class AABB, inheriting both A and B:
class AABB : public A, public B {...}
AABB could add some additional data fields and reimplement some of the interfaces, but it is not necessary.
Let's create and object of class AABB:
AABB* obj = new AABB ();
For example, obj points at address 0x8416e0. At this address starts data from ancestor class A. Data from ancestor class B starts with some offset (it should bw equal to sizeof (A)), for example, at 0x841700.
If we have some function f (B* b), and if we pass a pointer at AABB object to that function (like this: f (obj), obj is created above), actually not obj start address is passed, but rather a pointer at a start of B data section of AABB object.
Thus this misunderstanding of multiple inheritance inner works has led me to the problem I've got.
I guess Qobjects and multiple inheritance has been already treated. As an example: QObject Multiple Inheritance
I've been using SDL for some days now, and I decided after following some tutorials to start developing my own clone of Galaga. However, I had some difficulty trying to find a proper layout for my code.
For example, I have a Spaceship class defined as follows:
class Spaceship : public Sprite
{
public:
Spaceship(SDL_Surface *surface);
Spaceship(const char *filename);
void handleEvent(SDL_Event *event);
};
where Sprite is a base class that holds the position on the screen and so on.
My constructor would be something like:
Spaceship::Spaceship(SDL_Surface *surface) :
Sprite(surface)
{
m_y = Game::screenHeight() - m_surface->h; //positions the ship at the bottom
}
From what I've seen it's not possible to use Game::screenWidth() [static class] because I'd need to include "game.h", which is basically the main game class and includes "spaceship.h", creating basically an infinite loop (I've tried using #ifndef etc. with no success).
Is it possible to achieve this kind of result?
EDIT: I found a way to overcome the problem (I just added the "game.h" include in the cpp file and not in the header file).
If you only want to store pointers or references to those objects, then you can forward-declare one or both of the classes with class Game; or class Spaceship;. This is also fine if they take these objects as parameters or return them (with some exceptions, afaik).
If you actually want both to have a member of the other, then this is not possible, as each object would then have a copy of itself inside it.
You need to break a cycle in your dependency graph.
For example, one can add a field to your Spaceship class which saves a screen height.