Skip to content

class SF::Transformable
inherits Reference #

Decomposed transform defined by a position, a rotation and a scale

This class is provided for convenience, on top of SF::Transform.

SF::Transform, as a low-level class, offers a great level of flexibility but it is not always convenient to manage. Indeed, one can easily combine any kind of operation, such as a translation followed by a rotation followed by a scaling, but once the result transform is built, there's no way to go backward and, let's say, change only the rotation without modifying the translation and scaling. The entire transform must be recomputed, which means that you need to retrieve the initial translation and scale factors as well, and combine them the same way you did before updating the rotation. This is a tedious operation, and it requires to store all the individual components of the final transform.

That's exactly what SF::Transformable was written for: it hides these variables and the composed transform behind an easy to use interface. You can set or get any of the individual components without worrying about the others. It also provides the composed transform (as a SF::Transform), and keeps it up-to-date.

In addition to the position, rotation and scale, SF::Transformable provides an "origin" component, which represents the local origin of the three other components. Let's take an example with a 10x10 pixels sprite. By default, the sprite is positioned/rotated/scaled relatively to its top-left corner, because it is the local point (0, 0). But if we change the origin to be (5, 5), the sprite will be positioned/rotated/scaled around its center instead. And if we set the origin to (10, 10), it will be transformed around its bottom-right corner.

To keep the SF::Transformable class simple, there's only one origin for all the components. You cannot position the sprite relatively to its top-left corner while rotating it around its center, for example. To do such things, use SF::Transform directly.

SF::Transformable can be used as a base class. It is often combined with SF::Drawable -- that's what SFML's sprites, texts and shapes do.

class MyEntity < SF::Transformable
  include SF::Drawable

  def draw(target, states)
    states.transform *= self.transform
    target.draw(..., states)
  end
end

entity = MyEntity.new
entity.position = {10, 20}
entity.rotation = 45
window.draw entity

It can also be used as a member, if you don't want to use its API directly (because you don't need all its functions, or you have different naming conventions for example).

class MyEntity
  @transform : SF::Transformable
  forward_missing_to @transform
end

A note on coordinates and undistorted rendering: By default, SFML (or more exactly, OpenGL) may interpolate drawable objects such as sprites or texts when rendering. While this allows transitions like slow movements or rotations to appear smoothly, it can lead to unwanted results in some cases, for example blurred or distorted objects. In order to render a SF::Drawable object pixel-perfectly, make sure the involved coordinates allow a 1:1 mapping of pixels in the window to texels (pixels in the texture). More specifically, this means:

  • The object's position, origin and scale have no fractional part
  • The object's and the view's rotation are a multiple of 90 degrees
  • The view's center and size have no fractional part

See also: SF::Transform

Direct known subclasses

SF::Shape SF::Sprite SF::Text

Class methods#

.new #

Default constructor

View source

Methods#

#dup : Transformable #

Returns a shallow copy of this object.

This allocates a new object and copies the contents of self into it.

View source

#finalize #

Virtual destructor

View source

#inverse_transform : Transform #

get the inverse of the combined transform of the object

Returns: Inverse of the combined transformations applied to the object

See also: transform

View source

#move(offset : Vector2 | Tuple) #

Move the object by a given offset

This function adds to the current position of the object, unlike position= which overwrites it. Thus, it is equivalent to the following code:

object.position += offset

  • offset - Offset

See also: position=

View source

#move(offset_x : Number, offset_y : Number) #

Move the object by a given offset

This function adds to the current position of the object, unlike position= which overwrites it. Thus, it is equivalent to the following code:

pos = object.position
object.set_position(pos.x + offset_x, pos.y + offset_y)

  • offset_x - X offset
  • offset_y - Y offset

See also: position=

View source

#origin : Vector2f #

get the local origin of the object

Returns: Current origin

See also: origin=

View source

#origin=(origin : Vector2 | Tuple) #

set the local origin of the object

The origin of an object defines the center point for all transformations (position, scale, rotation). The coordinates of this point must be relative to the top-left corner of the object, and ignore all transformations (position, scale, rotation). The default origin of a transformable object is (0, 0).

  • origin - New origin

See also: origin

View source

#position : Vector2f #

get the position of the object

Returns: Current position

See also: position=

View source

#position=(position : Vector2 | Tuple) #

set the position of the object

This function completely overwrites the previous position. See the move function to apply an offset based on the previous position instead. The default position of a transformable object is (0, 0).

  • position - New position

See also: move, position

View source

#rotate(angle : Number) #

Rotate the object

This function adds to the current rotation of the object, unlike rotation= which overwrites it. Thus, it is equivalent to the following code:

object.rotation += angle

  • angle - Angle of rotation, in degrees
View source

#rotation : Float32 #

get the orientation of the object

The rotation is always in the range 0.0 ... 360.0

Returns: Current rotation, in degrees

See also: rotation=

View source

#rotation=(angle : Number) #

set the orientation of the object

This function completely overwrites the previous rotation. See the rotate function to add an angle based on the previous rotation instead. The default rotation of a transformable object is 0.

  • angle - New rotation, in degrees

See also: rotate, rotation

View source

#scale : Vector2f #

get the current scale of the object

Returns: Current scale factors

See also: scale=

View source

#scale(factor : Vector2 | Tuple) #

Scale the object

This function multiplies the current scale of the object, unlike scale= which overwrites it. Thus, it is equivalent to the following code:

scale = object.scale
object.scale = {scale.x * factor.x, scale.y * factor.y}

  • factor - Scale factors

See also: scale=

View source

#scale(factor_x : Number, factor_y : Number) #

Scale the object

This function multiplies the current scale of the object, unlike scale= which overwrites it. Thus, it is equivalent to the following code:

scale = object.scale
object.set_scale(scale.x * factor_x, scale.y * factor_y)

  • factor_x - Horizontal scale factor
  • factor_y - Vertical scale factor

See also: scale=

View source

#scale=(factors : Vector2 | Tuple) #

set the scale factors of the object

This function completely overwrites the previous scale. See the scale function to add a factor based on the previous scale instead. The default scale of a transformable object is (1, 1).

  • factors - New scale factors

See also: scale, scale

View source

#set_origin(x : Number, y : Number) #

set the local origin of the object

The origin of an object defines the center point for all transformations (position, scale, rotation). The coordinates of this point must be relative to the top-left corner of the object, and ignore all transformations (position, scale, rotation). The default origin of a transformable object is (0, 0).

  • x - X coordinate of the new origin
  • y - Y coordinate of the new origin

See also: origin

View source

#set_position(x : Number, y : Number) #

set the position of the object

This function completely overwrites the previous position. See the move function to apply an offset based on the previous position instead. The default position of a transformable object is (0, 0).

  • x - X coordinate of the new position
  • y - Y coordinate of the new position

See also: move, position

View source

#set_scale(factor_x : Number, factor_y : Number) #

set the scale factors of the object

This function completely overwrites the previous scale. See the scale function to add a factor based on the previous scale instead. The default scale of a transformable object is (1, 1).

  • factor_x - New horizontal scale factor
  • factor_y - New vertical scale factor

See also: scale, scale

View source

#transform : Transform #

get the combined transform of the object

Returns: Transform combining the position/rotation/scale/origin of the object

See also: inverse_transform

View source