UI

This article goes through how to use the Freecode canvas and the UI library.

How to use the canvas

Depending on what skeleton you are using, the way you add your graphics to the canvas differs. The templates for either skeleton will include an example of using the canvas.

If you use BasicChallenge (or no skeleton) you will want to manually add the elements to the canvas, like so:

    def setup_canvas(self):
        self.my_rectangle = Rectangle(x=10, y=10, color="green", parent=self.canvas)

If you use StageChallenge or GameChallenge you will want to return the element in the setup_view method:

    def setup_view(self):
        self.my_rectangle = Rectangle(color="green")
        return self.my_rectangle

Note that you neither specify parent nor position in setup_view, this is done for you

Overview

The UI library is object oriented, meaning that the graphical elements are represented by Python objects. You create a new element by creating a new object and you can modify the elements by modifying the objects. An element will not show up on the canvas unless the object has the canvas as a parent (or grand parent).

A child element will inherit some of the attributes from it's parent. They will be positioned relative to the parent, scaled according to the parent, and opacity of the parent is applied. A child with opacity of 0.5 and with a parent with opacity of 0.5 will in effect have an opacity of 0.25.

When creating an element object, you can (and sometimes must) include a number of attributes. You can use any of the names listed here, e.g. width or w or size_x. The same names can be used to get or modify the attributes later on. Here is an example of this:

my_rect = Rectangle(w=8, h=6, x=10, y=12, parent=self.canvas)
my_rect.width = 4
my_rect.color = "blue"

All elements can have a parent, and some can have children. If an element switches parent it will be removed from the previous parent's list of children. You can either use the parent attribute or the .add_child(child)/.remove_child(child) methods to update the heirarchy. But remember that for an element to show up in the canvas it needs to have it as an ancestor.

The following section and subsections will detail the different elements available in the UI library, grouped by similarities. Many elements have common attributes, which are detailed in their own section to make things cleaner.

Elements

All these elements can be imported from the lib.ui package, along with any of the enums and constants listed here.

As an example:

from lib.ui import Rectangle, Text

my_rect = Rectangle(children=[Text("Hello")])

Remember to add the element to the import list, or you will get an error.

Shapes

These elements are used to make geometric shapes, either filled or outlines. Use Polygon to make additional shapes such as triangles and hexagons. For more complex shapes, consider using images instead.

Rectangle

Use to make squares, rectangles and rounded rectangles.

General attributes: common, container, shape, action, click, drag, keyboard

corner_radius - float | None S

Add rounded corners to the rectangle

Rectangle(w=10, h=5, x=10, y=10, color="green", corner_radius=1)

Circle

Use to make circles.

General attributes: common, container, shape, action, click, drag, keyboard

radius/r - float S

The radius of the circle, use instead of width/height

min_radius/min_r - float

The minimum radius for this element, does not affect the current radius

max_radius/max_r - float

The maximum radius for this element, does not affect the current radius

fixed_radius - bool

Prevents automatic resizing of the circle

Circle(r=20, color="blue", stroke=2)

Polygon

Use to make any other straight edge shapes. Consider using images if you need a large number of points.

General attributes: common, container, shape, action, click, drag, keyboard

points - list[tuple[float, float]] R

A list of points to use to draw the polygon, required and positional

bounds - tuple[tuple[float, float], tuple[float, float]] S

The bounds of the polygon used to determine size and pivot, calculated if omitted

Polygon([(0, -5), (5, 5), (-5, 5)], color="red")

ComplexShape

Use to make a shape with straight or Bézier curves. Consider using images if you need very complex shapes or a large number of points.

General attributes: common, container, shape, action, click, drag, keyboard

segments - list[list[tuple[float, float]]] R

A list of segments (list of points) to use to draw the shape, required and positional

Each segment must consist of one to three points (first must be one point):

• Single point means a straight line to that point
• Two points is a quadratic Bézier curve with a control point (first) and an end point (second)
• Three points is a cubic Bézier curve with two control points and an end point (last)

bounds - tuple[tuple[float, float], tuple[float, float]] S

The bounds of the shape used to determine size and pivot, calculated if omitted

closed - bool S

Whether the shape should be closed or not

ComplexShape([[(0, 0)], [(5, 5), (0, 10)], [(10, 10)], [(5, 5), (15, 5), (10, 0)]], color="green")

Text

These elements can be used to display text.

Text

Simple text element. The size is based on the text string and font size.

General attributes: common, action, click, drag, keyboard

text - str

The text to display, required and positional

color - str

The text color

font_size - float

The text font size

align_x - "left" | "right" | "center"

The horizontal text align

Text("Hello World!", font_size=10, color="yellow")

DynamicText

Alternative to Text where the text is adjusted to fit within the size rather than the other way around. You can use .fit_to_content() to calculate the size based on the text and font size (useful together with min and max size).

General attributes: common, action, click, drag, keyboard

text - str

The text to display, required and positional

color - str

The text color

font_size - float

The text font size

align_x - "left" | "right" | "center"

The horizontal text align

align_y - "top" | "bottom" | "center"

The vertical text align

DynamicText("Hello World!", font_size=10, color="yellow", w=40, h=10)

HtmlArea

Use to add a block of text that can be formatted using HTML code. If the content is wider or taller than the element size, a scrollbar will appear. It is possible to include images and CSS, using normal HTML syntax.

General attributes: common, scroll

html - str

The HTML text to display, required and positional

font_size - float

The text font size

align_x - "left" | "right" | "center"

The horizontal text align

HtmlArea("Hello <b>World</b>!", font_size=5, w=50, h=20)

Graphics

These elements can be used to display images and animations.

Image

Displays a static image.

General attributes: common, action, click, drag, keyboard

image - str S

The name of the image to show

color - str

A color to use for tinting the image

Image("TODO", w=30, h=30, opacity=0.75)

Sprite

Displays an animated image.

General attributes: common, action, click, drag, keyboard

image - str S

The name of the image to show

color - str

A color to use for tinting the image

animation/anim - str S

The name of the animation to play, use "default" for the default animation

start_frame/start - int | None S

An animation frame to start on

end_frame/end - int | None S

An animation frame to end on

Sprite("TODO", w=30, h=30)

Containers

These elements can be used to fit more content in the canvas.

ScrollArea

Use when you want some content to be scrollable (vertical and/or horizontal).

General attributes: common, scroll

scroll = ScrollArea(w=40, h=20)
Text("Hello World!", font_size=20, parent=scroll)

TabArea

Use when you want to split up some content into tabs. Consider putting tab content into ScrollAreas for even more space.

General attributes: common, style

tabs - dict[str, BaseElement]

The tab names and content to include, required and positional, constructor only

font_size - float

The font size to use for the tab headers

red = Rectangle(color="red", children=[Text("R", font_size=20)])
green = Rectangle(color="green", children=[Text("G", font_size=20)])
blue = Rectangle(color="blue", children=[Text("B", font_size=20)])
TabArea({"Red": red, "Green": green, "Blue": blue}, w=30, h=50)

Layouts

These elements can be used to simplify positioning of elements. They handle adddion, removal and resizing of elements as well.

Horizontal

Use to position elements horizontally.

General attributes: common, Layout

All positional arguments are added as children

Horizontal(Rectangle(color="yellow"), Rectangle(color="magenta"), Rectangle(color="cyan"))

Vertical

Use to position elements vertically.

General attributes: common, Layout

All positional arguments are added as children

Vertical(*[Text(str(i)) for i in range(5)], spacing=5)

Grid

Use to position elements in a grid.

General attributes: common, Layout

All positional arguments are added as children

columns - int

Number of columns in the grid, required

Grid(*[Text(str(i)) for i in range(20)], columns=5, w=30, h=30, spacing=5)

Controls

These elements are interactive UI elements mostly useful in interact mode.

Button

Use to create a button.

General attributes: common, style, action, click

text - str

The text on the button, required and positional

font_size - float

The font size of the button text

align_x - "left" | "right" | "center"

The horizontal text align

align_y - "top" | "bottom" | "center"

The vertical text align

padding - float

Padding around the text within the button

border_size - float | None

The thickness of the border around the button

corner_radius - float | None

The radius of the corners of the button, set to None for a square button

overlay - bool

Whether to use the overlay styling for this button or not

primary - bool

Whether to use the primary styling for this button or not

enabled - bool S

If set to False will both disable click callbacks and use the disabled styling

def callback(event):
    print("Button clicked!")

Button("Click me!", on_click=callback)

Checkbox

Use to create a checkbox.

General attributes: common, style, action, click

checked - bool S

Whether the checkbox is checked or not

intermediate - bool S

Whether the checkbox is in an intermediate state or not

intermediate_value - bool

The checked value to use when the checkbox is in an intermediate state

text - str | None

The label next to the checkbox

font_size - float

The font size of the checkbox label

solid - bool S

Whether to use the solid icons for this checkbox or not

enabled - bool S

If set to False will both disable click callbacks and use the disabled styling

on_change - (CheckboxEventData) -> None E

Called whenever the checkbox changes state

def callback(event):
    print("Checkbox was checked" if event.checked else "Checkbox was unchecked")

Checkbox(scale=4, on_change=callback)

Panels

These elements can be used to visually separate a set of other elements.

Panel

A simple panel.

General attributes: common, style

corner_radius - float | None

The radius of the corners of the panel, set to None for a square panel

overlay - bool

Whether to use the overlay styling for this panel or not

Panel(w=50, h=50, children=[Circle(r=20)])

Toolbar

A penel with three distinct areas: left, right, and center. Children within each area are arranged horizontally.

General attributes: common, style

corner_radius - float | None

The radius of the corners of the panel, set to None for a square panel

overlay - bool

Whether to use the overlay styling for this panel or not

spacing - float

The distance between children within each area

padding - float

The distance between toolbar content and the outer edge

Toolbar(
    w=80,
    h=10,
    fixed_height=True,
    left_children=[Circle()],
    right_children=[Rectangle()],
    center_children=[Text("TOOLBAR")],
)

Popup

A popup panel with a message and ability to add buttons. The popup needs to be activated by toggling. Clicking any of the popup buttons will close the popup. Only works properly in interact mode.

General attributes: common, style

text - str R

The message to display, required and positional, constructor only

buttons - list[Button] R

The buttons to include, required and positional, constructor only

corner_radius - float | None

The radius of the corners of the panel, set to None for a square panel

overlay - bool

Whether to use the overlay styling for this panel or not

spacing - float

The distance between buttons

padding - float

The distance between popup content and the outer edge

def callback(event):
    print("Deal!")

buttons = [Button("OK", primary=True, on_click=callback), Button("Cancel")]
popup = Popup("My Popup!", buttons, w=30, h=15, anchor_y=1, y=-5)
Rectangle(size=10, hover_targets=[popup], children=[popup])

Specialized

These elements are not as generally useful as the others, but are very useful for specific tasks.

Board

Use to create a chess-like game board of square grids. If you need something more dynamic or want more features, take a look at world.

You can place elements on the board by coordinates, e.g. board[0, 2] = Circle(color="red"). The elements will automatically be positioned and resized to match the specified square. There can only be one element at each coordinate, which can be fetch like so: board[0, 2].

General attributes: common, style

rows - int R

How many rows the board should have

columns - int R

How many columns the board should have

line_size - float

The thickness of the grid lines

edge_size - float

The thickness of the edge outside the grid

font_size - float

The font size of the square coordinate labels

row_labels - list[str] R

The labels to use for the rows, you can use the constants LOWERCASE_LABELS, UPPERCASE_LABELS, and NUMBER_LABELS

column_labels - list[str] R

The labels to use for the columns, you can use the constants LOWERCASE_LABELS, UPPERCASE_LABELS, and NUMBER_LABELS

invert_rows - bool R

Will draw the rows bottom to top rather than top to bottom

invert_columns - bool R

Will draw the columns right to left rather than left to right

corner_radius - float | None

The radius of the corners of the board, set to None for a square panel

overlay - bool

Whether to use the overlay styling for this board or not

def callback(event):
    event.source.color = "orange"

board = Board(size=80)
for r in range(board.rows):
    for c in range(board.columns):
        board[r, c] = Circle(scale=0.9, color="green", on_click=callback)

Stage

This element is primarily used by the StageChallenge and GameChallenge skeletons. It is recommended to use those rather than using this element directly.

General attributes: common, style

content - BaseElement R

The main content to put in the middle of the stage, required and positional, constructor only

info_panel - BaseElement | None R

Optional content to put on the left-hand side, constructor only

tabs - dict[str, BaseElement] R

Tabs to show on the right-hand side, constructor only

show_toolbar - bool R

Whether to show the toolbar or not, constructor only

center_buttons - list[Button] R

Buttons to put in the center of the toolbar, constructor only

right_buttons - list[Button] R

Buttons to put to the right of the toolbar, constructor only

info_prompt - str

Text to show in the toolbar on the lower left

spacing - float

Distance between the areas of the stage

toolbar_height - float

The height of the toolbar

Attributes

This section lists the attributes common among several elements, check each element above for which attributes apply.

A few attributes are marked with a letter, they have the following meanings:

C - coordinate

This attribute is a coordinate property, see coordinates

E - event callback

This attribute is an event callback, see events

R - readonly

This attribute can not be updated (or animated)

S - static

This attribute can not be animated, see animation

Common

parent - Container | None S

The parent of the element

size - tuple[float, float] C

The size (width and height) of the element

Some elements calculate these values based on other attributes, in which case the size is readonly

You can use .request_size(size, time)/.request_size(size, time)/.request_size(size, time) to change the size instead, which will take into account min and max size as well

size_x/width/w - float

The width of the element, component of size

size_y/height/h - float

The height of the element, component of size

min_size - tuple[float, float] C

The minimum size of the element, does not apply automatically and does not prevent setting the size manually

min_size_x/min_width/min_w - float

The minimum width of the element, component of min_size

min_size_y/min_height/min_h - float

The minimum height of the element, component of min_size

max_size - tuple[float, float] C

The maximum size of the element, does not apply automatically and does not prevent setting the size manually

max_size_x/max_width/max_w - float

The maximum width of the element, component of max_size

max_size_y/max_height/max_h - float

The maximum height of the element, component of max_size

fixed_width - bool

If set to True then the width will not be changed automatically, can still be changed manually though

fixed_height - bool

If set to True then the height will not be changed automatically, can still be changed manually though

position/pos - tuple[float, float] C

The position of the element, relative to the anchor (usually center of the element)

position_x/pos_x/x - float

The x-position of the element, component of position

position_y/pos_y/y - float

The y-position of the element, component of position

offset - tuple[float, float] C

An offset to apply to the element position, useful if the position is controlled by another element

offset_x - float

The x-offset of the element, component of offset

offset_y - float

The y-offset of the element, component of offset

anchor - tuple[float, float] C

The anchor point of the element, 0 means center, -1 means left/top and 1 means right/bottom.

anchor_x - float

The x-anchor of the element, component of anchor

anchor_y - float

The y-anchor of the element, component of anchor

z_index/z - float

The visual sorting of the element or "distance from the screen", an element with higher z-index will be drawn above others

Children will have the same z-index as their parents from the outside

scale - tuple[float, float] C

Scaling factor for the element, is not considered when estimating the size or position of the element

scale_x - float

The x-scale of the element, component of scale

scale_y - float

The y-scale of the element, component of scale

rotation - float

The rotation of the element in degrees, positive values means clockwise and negative means counter-clockwise

pivot - tuple[float, float] C

The pivot point of the element, which is used as the rotation point

Note: does not work properly for Text, Image, and Sprite

pivot_x - float

The x-pivot of the element, component of pivot

pivot_y - float

The y-pivot of the element, component of pivot

toggle_group - str | None

The toggle group of the element, see toggling

toggle_by_default - bool

Whether the element should start out toggled on

opacity - float

The opacity of the element, 1 means fully opaque and 0 means fully transparant

on_resize - (ResizeEventData) -> None E

Called after the element is given a new size

Container

children - list[BaseElement] R

Elements to add as children

on_add_child - (ChildEventData) -> None E

Called when a (public) child is added to the container

on_remove_child - (ChildEventData) -> None E

Called when a (public) child is removed from the container

Shape

color - str

The fill or stroke color of the shape

stroke - float | None S

Draw the edge of the shape rather than the area

Action

action_effect - Effect | None

Effect to apply when hovering the element and it is interactable

hover_effect - Effect | None

Effect to apply when hovering the element

hover_targets - list[BaseElement]

Elements that will be toggled while this element is hovered

Click

on_click - (ClickEventData) -> None E

Called when this element is clicked in interact mode

click_targets - list[BaseElement]

Elements that will be toggled when this element is clicked

interact_click_targets - list[BaseElement]

Same as click_targets but only works in interact mode

Drag

draggable - bool | None S

Whether the element should be draggable, set to None for default behaviour

on_drop - (DragEventData) -> None E

Called when this element is dropped after being dragged

drag_targets - list[BaseElement]

Elements that will be toggled while this element is dragged

drag_effect - Effect | None

Effect to apply when the element is being dragged

Keyboard

key_list - list[str] S

Keys this element should listen for, see keys

on_key_up - (KeyboardEventData) -> None E

Called when a key is released (if in key_list or it is empty)

Scroll

widget_color - str

The color of the scroll bars

widget_size - float S

The size of the scroll bars

follow_bottom - bool

If set to True then the area will continue scrolling automatically if at the bottom

Layout

spacing - float

Distance between elements

align_x - "left" | "right" | "center"

The horizontal element align

align_y - "top" | "bottom" | "center"

The vertical element align

Style

style - Style

The style to apply to this element, see Styling

The attributes marked with a C is a coordinate attribute. This means that it has two component attributes for the x and y values. You can modify either of these three attributes (or any aliases) to change (part) of the coordinate.

The coordinate property has some additional convenience features:

• Vector operations such as addition, subtraction, multiplication and division
• Conversion of scalar values to a pair

This menas that we can write code like this:

rect = Rectangle()
rect.size = 20       # set size to (20, 20)
rect.pos += (5, 10)  # add (5, 10) to position
rect.anchor -= 1     # subtract (1, 1) from anchor
rect.scale *= 2      # multily scale by 2

You can also access the x and y elements of the coordinates as members, e.g. rect.pivot.x, but you can not assign to them, so it is better to always use rect.pivot_x.

Animation

Many attributes are animated when modified, such as gradually turning transparent when setting opacity to 0. But it is possible to control this in more detail using the animation features of the UI library.

You can specify the values of many attributes with more precise timing using the .time(time) method. It returns a virtual copy of the element which represents the element at that time. The time should be a number from 0 to 1.

Here is an example of creating a shaking animation:

# setup_canvas / setup_view
self.box = Rectangle()

# update_canvas / update_view
self.box.time(0.2).rotation = 15
self.box.time(0.4).rotation = -10
self.box.time(0.6).rotation = 10
self.box.time(0.8).rotation = -15
self.box.time(1).rotation = 0

You might realize that you do not want an attribute to be animated, in which case you can use .instant which is the same as .time(0). This will ensure that the value change occurs immediately without any intermediate values.

Effects

It is possible to apply effects on some attributes while certain conditions are met, such as when an element is hovered over with the mouse. This is specified using the Effect object and effect attributes, such as hover_effect.

The Effect object has support for the following attributes:

• color
• opacity
• rotation
• scale or scale_x/scale_y

The specified values will be applied while the condition is met, and reverted once it is not.

Here is an example of a hover effect on a circle:

Circle(r=30, color="blue", hover_effect=Effect(color="orange"))

Many times you would want an effect only when an element is interactable. For this we have the action_effect attribute.

In this example the circle will only be interactable when clickable:

Circle(r=30, color="blue", action_effect=Effect(color="orange"), on_click=lambda e: setattr(e.source, "color", "green"))

Effects of child elements will trigger if the effect of the parent would trigger.

Events

There are several events that can be listened to in order to react to element changes or user input. The easiest way to do this is to use to on_[event] attributes. These attributes takes callbacks, which are functions with a single parameter which will be an EventData object. Look at the example for Button, or the last example of the previous section.

The subsections lists the additional attributes that are available for the different kinds of EventData objects.

ResizeEventData

source - BaseElement

The source element of the event

time - float | None

The time of the change, see animation

dimensions/dims - Dimensions

The dimensions affected by the change

ChildEventData

source - BaseElement

The source element of the event

child - BaseElement

The child in question

ClickEventData

source - BaseElement

The source element of the event

DragEventData

source - BaseElement

The source element of the event

position/pos - tuple[float, float]

The drop position

position_x/pos_x/x - float

The x-component of the drop position

position_y/pos_y/y - float

The y-component of the drop position

KeyboardEventData

source - BaseElement

The source element of the event

key - str

The pressed key, see keys

CheckboxEventData

source - BaseElement

The source element of the event

checked - bool

The new checked value

intermediate - bool

The new intermediate value

Keys

The key value in KeyboardEventData or the key_list attribute can either be a character matching the key (accounting for modifiers (e.g. shift or alt) and keyboard layout) or a special value corresponding to the key. The following table list some convenient constants that can be used:

Constant	Key
Key.UP	Up arrow
Key.DOWN	Down arrow
Key.LEFT	Left arrow
Key.RIGHT	Right arrow
Key.SPACE	Spacebar
Key.ENTER	Enter key

You can also check keyboard values yourself using the following code snippet (need to be in interact mode):

Rectangle(opacity=0, parent=self.canvas, on_key_up=lambda e: print(e.key))

Toggling

This section covers the toggling system which can be used to create lightweight interactable UI. It is used for tabs and popups, but can be used for other purposes as well.

Toggling can be triggered by hovering, clicking or dragging using hover_targets, click_targets and drag_targets. When an element is added as part of these lists, it will automatically be hidden and only shown once toggled. This can be avoided by setting toggle_by_default to True on the element in question.

It is possible to group together elements in a toggle group by setting toggle_group to the same value for all elements. When elements are in a group at most one of the elements can be toggled on at a time. The toggling logic is slightly modified for elements within a toggle group, particularly they will not toggled off unless another element is toggled on.

Here is an example of creating a tooltip:

tooltip_text = Text("My tooltip")
tooltip = Panel(size=tooltip_text.size + 3, y=-5, children=[tooltip_text])
Circle(children=[tooltip], hover_targets=[tooltip])

Styling

Some elements have a style attribute which will be used to determine color and opacity. This Style object can be replaced with a custom style object to have different styling.