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Help => Graphics => Topic started by: Kanefa on October 25, 2014, 11:52:57 am

Title: sf::Transformable
Post by: Kanefa on October 25, 2014, 11:52:57 am

I am having confusion when using sf::Transformable.

I have a class called Button that inherits sf::Transformable. My motivation to do this is I want to be able to set the position of the entire class with a single sf::Transformable::setPosition. This works.

Next, I create another class called ToggleButton that inherits from sf::Transformable and is composed of two Buttons. My motivation is the same. I want to be able to set the position of the entire class with a single single sf::Transformable::setPosition. This works.

However, I run into a problem with Button::handler(). The handler is comparing the position of the button with the position of the mouse. The problem is Button::handler() does not take into account the transform (setPosition) that occurs to ToggleButton.

When drawing the elements this is not an issue, because by inheriting from sf::Drawable I can easily apply the transform within sf::Drawable::draw with

states.transform *= getTransform();

One solution I see is for ToggleButton not to inherit from sf::Transformable. Then simply call sf::Transformable::setPosition on each Button member variable. However, I am curious to understand how I should be properly using sf::Tranformable in such situations. How do I "string" multiple transforms like this together?

Title: Re: sf::Transformable
Post by: Nexus on October 25, 2014, 12:03:11 pm

In case the handler() method should be called directly on one of the two child buttons, the Button class must be aware if it is a child. This can be done by storing a parent pointer ToggleButton* (or in general, sf::Transformable or an intermediate interface class). Button::handler() would then check whether the parent is no null pointer, and multiply its transform with the current one.

Otherwise, if you don't want a Button to know about its parent ToggleButton, you could pass a transform argument to handler().

By the way, are you only using the transforms for position? Do you test something like sf::FloatRect::contains()?

Title: Re: sf::Transformable
Post by: Kanefa on October 25, 2014, 02:47:29 pm

I  updated Button::handler's signature from

void handler(const sf::RenderWindow& window, const sf::View& view);

to

void handler(const sf::RenderWindow& window, const sf::View& view, sf::Transformable* transformable = nullptr);

and then I am able to apply the transform to my rect

sf::FloatRect buttonRect(getPosition().x, getPosition().y, mSize.x, mSize.y);
if (transformable)
   buttonRect = transformable->getTransform().transformRect(buttonRect);

This works. Now I am wondering if my motivation to use sf::Transformable is intended. The ToggleButton class inherits sf::Transformable, because I like how it "creates" a coordinate system for that object. For instance, within the ToggleButton object I can place a Button button0 at (0,0) and then I can place Button button1 at (button0.width + buffer, 0). Then I can set the position of the entire instance of the ToggleButton object in the game world. Granted, I only care about  the position (and not rotation, scaling, etc), but is this the intended usage?

Quote from: Nexus on October 25, 2014, 12:03:11 pm

By the way, are you only using the transforms for position? Do you test something like sf::FloatRect::contains()?

Yes and yes.