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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:

Manually adding elements to canvas 
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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:

Implicitly adding element to canvas 
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def setup_view(self):
    self.my_rectangle = Rectangle(color="green")
    return self.my_rectangle

Note

You specify neither parent nor position in setup_view, this is done for you.

Either way you will get a canvas containing only a green square.

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 grandparent, or great grandparent, and so on).

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.

Accessing attributes 
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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 hierarchy. 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.

Importing and using an element 

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from lib.ui import Rectangle, Text

my_rect = Rectangle(children=[Text("Hello", color="white", font_size=30)])

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

All elements extend either the BaseElement or ContainerElement base class which provides the common and container attributes and methods.

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

Used to make squares, rectangles and rounded rectangles.

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

corner_radius - float | None S
Add rounded corners to the rectangle
Creating three Rectangle objects 

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self.my_rectangle = Rectangle(color="white", children = [

    # Wide rectangle
    Rectangle(w=4, h=2, x=0, y=0, color="#FF6347"),

    # Rotated square
    Rectangle(w=2, h=2, x=-1, y=-1, color="red", rotation=60),

    # Hollow square
    Rectangle(w=2, h=2, x=0, y=0, color="green", rotation=-20, stroke=0.2, opacity=0.3)
])

Circle

Used to make circles.

General attributes/methods: 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
Creating three Circle objects 

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self.my_rectangle = Rectangle(color="white", children = [

    # Red circle
    Circle(r=1, color="red", x=-1),

    # Blue circle
    Circle(r=1, color="blue", x=1, y=1),

    # Green ring
    Circle(r=0.8, color="green", x=0, y=1, stroke=0.1)
])

Polygon

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

General attributes/methods: 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
Creating three Polygon objects 

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self.my_rectangle = Rectangle(color="white", children = [
    # Red triangle
    Polygon([(0, 0), (5, 0), (2, 1)], color="red", x=0.4, y=0, z_index = 1),

    # Blue line
    Polygon([(0, 0), (0, 2), (0.5, 2), (1, 1), (2, 2), (1, 0)], color="blue", x=-1.5, y=0, stroke=0.3, z_index=3),

    # Green quadrilateral
    Polygon([(0, 0), (-2, 2), (2, 2), (3, 0)], color="green", x=0, y=0, opacity=0.5, rotation=170, z_index=2)
])

ComplexShape

Used 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/methods: 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
Creating a ComplexShape 

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self.my_rectangle = Rectangle(color="white", children = [
    ComplexShape([[(0, 0)], [(5, 5), (0, 10)], [(10, 10)], [(5, 5), (15, 5), (10, 0)], [(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/methods: 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
Creating a Text 

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self.my_rectangle = Rectangle(color="white", children = [
    Text("Hello\nWorld!", font_size=5, color="orange")
])

DynamicText

Alternative to Text where the text is adjusted to fit within the size rather than the other way around.

General attributes/methods: common, action, click, drag, keyboard, fit to content

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
Creating a DynamicText 
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self.my_rectangle = Rectangle(color="white", children = [
    DynamicText("Hello\nWorld!", font_size=5, color="orange", w=10)
])

HtmlArea

Used 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/methods: 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
disable_scroll - bool
Disables scroll and all ScrollArea features so it will limit the HtmlArea to its width and height.
disable_auto_font_scale - bool
Disables auto font scale and the text font size will be applied.
Creating an HtmlArea 

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self.my_rectangle = Rectangle(color="white", children = [
    HtmlArea("Hello <b>World</b>!", font_size=4, w=15, h=15, disable_scroll=True, disable_auto_font_scale=True)
])

Graphics

These elements can be used to display images and animations.

Image

Displays a static image.

General attributes/methods: 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
Creating three Image objects 

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self.my_rectangle = Rectangle(color="white", children = [
    # Left cat
    Image("std_katniss_standing.webp", w=4, h=3),

    # Slightly squished cat
    Image("std_katniss_standing.webp", w=4, h=2, x=4, y=1.5),

    # Red background cat
    Image("std_katniss_standing.webp", w=8, h=4, x=2, y=2, rotation=20, color="red", opacity=0.3, z_index=-1, scale_x=-1)
])

Note

There are many images provided by the framework that can be accessed simply by using their names as the image string. You can find them all in Built in images.

Sprite

Displays an animated image. See Create Sprite Sheet to learn about creating a sprite sheet.

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

image - str S
The name of the sprite sheet 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
Creating three Sprite objects 

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a = Sprite("weird_sheet.png", w=2, h=2, x=1, y=1)
b = Sprite("weird_sheet.png", w=2, h=2, x=3, y=1, start=2, end=0, scale_x=-1)
c = Sprite("weird_sheet.png", w=1.5, h=2, x=5, y=1, animation="just_display_guy")

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/methods: common, scroll

Creating a ScrollArea 
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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/methods: 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
Creating a TabArea 
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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 addition, removal and resizing of elements as well. Also, these elements cascade resizing down to any children. Other elements like Rectangle are resized if the parent is a Layout element, but a Rectangle doesn't cascade resizing to its children.

Horizontal

Used to position elements horizontally.

General attributes/methods: common, layout

All positional arguments are added as children.

proportions - list[float]
Proportions of size to give to each element, 0 means an even proportion of the remaining space
Creating a Horizontal 

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

Vertical

Used to position elements vertically.

General attributes/methods: common, layout

All positional arguments are added as children.

proportions - list[float]
Proportions of size to give to each element, 0 means an even proportion of the remaining space
Creating a Vertical 

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

Grid

Used to position elements in a grid.

General attributes/methods: common, layout

All positional arguments are added as children.

rows - int
Number of rows in the grid, calculated if not set
columns - int
Number of columns in the grid, calculated if not set
transpose - bool
Whether to place columns first, rather than rows first
alignments - tuple[list["left" | "right" | "center" | None], list["top" | "bottom" | "center" | None]
Alignments for each column or row and column, None means use the align_x/align_y value
proportions - tuple[list[float], list[float]
Proportions of size to give to each row and column, 0 means an even proportion of the remaining space
Creating a Grid 

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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

Used to create a button.

General attributes/methods: common, style, action, click, fit to content

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

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

Checkbox

Use to create a checkbox.

General attributes/methods: 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
Creating a Checkbox 
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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. Can have a title and a title image. Can also have content with will be resized based on the panel size.

General attributes/methods: common, style

content - BaseElement R
Content to but inside the panel, constructor only
title - str R
A title for the panel, constructor only
title_image - str
An image to put in the top-right corner of the panel, only visible if a title is set
font_size - float
The font size of the title text
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 the title and content
padding - float
The distance between panel content/title and the outer edge
Creating a Panel 

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Panel(w=50, h=50, content=Circle(color="blue"), title="My Panel")

Toolbar

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

General attributes/methods: 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
Creating a Toolbar 

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

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/methods: 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
Creating a Popup 
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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/methods: 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
Creating a Board 

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

board = Board(size=64)
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/methods: 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

SpeechBubble

Use to create a speech bubble. Mainly used by the .say(...) command for character actors in World.

General attributes/methods: common, fit to content

text - str S
The text within the speech bubble, required and positional
font_size - float S
The desired text font size
settings - SpeechBubbleSettings S
Specifies the shape of the speech bubble:
  • radius - The radius of the speech-bubble "corners"
  • tail_inset - How far in the tail should be positioned (x-offset)
  • tail_width - How thick the tail should be
  • tail_height - How tall the tail should be
  • tail_point_offset - How the tail tip should be positioned (x-offset)
  • tail_position - Where to put the tail, one of "bottom_left", "bottom_right", "top_left", or "top_right"
  • shadow_height - How high up the lower shading of the bubble should go
  • edge_size - How thick the edge around the bubble should be
theme - SpeechBubbleTheme
Specifies the color scheme of the speech bubble:
  • text_color - The color of the text
  • bubble_color - The background color of the bubble
  • shadow_color - The shading color of the bubble
  • edge_color - The color of the bubble edge
auto_fit - bool
Whether to automatically resize the bubble to fit the text or not, can use .fit_to_content() manually
auto_anchor - bool
Whether to automatically anchor the element position to the tail tip or not, can use .anchor_at_tail() manually

Table

Extends the Grid element with grid lines. It is recommended to use a data manager.

Almost identical to Grid, but with the following additional attributes:

style - Style
See styling
line_size - float | None
The thickness of the grid lines, use None to remove the lines

Attributes / Methods

This section lists the attributes and methods common among several elements, check each element above for which 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 read-only
.request_size(size)
Ask the element to adjust its size to match the given size, taking into account min and max size and other restrictions
.request_size(size, time)
Same as above but using an animation time, see Animation
size_x/width/w - float
The width of the element, component of size
.request_width(width)
Ask the element to adjust its width to match the given width, taking into account min and max width and other restrictions
.request_width(width, time)
Same as above but using an animation time, see Animation
size_y/height/h - float
The height of the element, component of size
.request_height(height)
Ask the element to adjust its height to match the given height, taking into account min and max height and other restrictions
.request_height(height, time)
Same as above but using an animation time, see Animation
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

pivot 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 if in constructor otherwise a read-only list of current children
.add_child(child)
Add a new child to the element, removing it from any previous parent
.add_children(child_1, child_2, ...)
Add several new children to the element
.remove_child(child)
Removes a child from the element
.remove_children(child_1, child_2, ...)
Removes several children from the element
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

FitToContent

.fit_to_content()
Ask element to adjust its size based on the content
.fit_to_content(time)
Same as .fit_to_content() but at the given animation time

Coordinates

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
Using coordinates 
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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.

Note

To get animation to work, go to the Graphics tab in Freecode Creator and check "Uses Canvas" and "Has Canvas Animation".

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 0.0 to 1.0 which corresponds to a fraction of the time step, where 0.0 is at the start, 0.5 is at the middle, and 1.0 is at the end of the time step.

Creating a shaking animation 
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# 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). If you want it to happen later in the time step you can first add the old value with a time value, and then the new value with a slightly higher time value e.g. .time(0.499) and then the new value with time(0.5). This will ensure that the value change occurs immediately without any intermediate values.

Making boxes suddenly transparent 
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# setup_canvas / setup_view
self.box_0 = Rectangle()
self.box_1 = Rectangle()
self.box_2 = Rectangle()

# update_canvas / update_view
self.box_0.instant().opacity = 0.5

self.box_1.time(0).opacity = 0.5

self.box_2.time(0.499).opacity = 1.0
self.box_2.time(0.5).opacity = 0.5

Step animation

It is possible to go to the next time step manually, this can be very useful when making more elaborate animations. You do this by calling canvas.split_step(). All graphical operations performed after canvas.split_step() will occur in a new step.

Example: Falling rectangle

We want to have a rectangle that tips over and lands on one side. The rectangle should be 2 units wide, 8 units high, and have its pivot offset from the center to its lower right corner. We will also offset it 6 units to the right and 9 units down to make it easier to see. If we do all this it should be placed like in the image below:

Note

The coordinate (0, 0) is in the upper left corner, x grows to the right, and y grows downwards.

Note

The grey dots show all points that have integer coordinates, i.e. (1, 1), (2, 1), and so on.

Code for defining our rectangle 
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self.falling_rect = Rectangle(w=2, h=8, x=6, y=9, color="red", pivot_x=1, pivot_y=4)

We don't want the rectangle to suddenly hit the ground. To make the fall look somewhat natural we will divide it up like this:

  • The rectangle will stand still for one time step
  • The rectangle will rotate 45 degrees the first 70% of the second time step
  • The rectangle will rotate 45 degrees more during the remaining 30% of the second time step

Code for defining our rectangle's fall 
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# No animation in the first step
self._context.canvas.split_step()
# In the first 70% of the step the rectangle falls 45 degrees
self.falling_rect.time(0.7).rotation = -45
# In the remaining 30% the rectangle falls the rest of the way
self.falling_rect.time(1.0).rotation = -90

The end result will look like this:

Freecode that implements this animation: Freecode

Note

You need to be logged in to see the freecode

Warning

The freecode uses the old graphics style found in Freecode graphics

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.

Hover effect on a circle 
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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.

Making a circle interactable only when clickable 
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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
Key.DOWN Down
Key.LEFT Left
Key.RIGHT Right
Key.SPACE Space
Key.ENTER Enter
Manually check keyboard value (only works in interact mode) 
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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.

Example of creating a tooltip 
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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.