gui-cs.Terminal.Gui/docfx/docs/drawing.md

Drawing (Text, Lines, and Color)

Terminal.Gui provides a set of APIs for formatting text, line drawing, and character-based graphing. The fundamental concept is a Cell which ocupises a particular row and column in the terminal. A Cell includes the character (glyph) that should be rendred by the terminal, and attributes that indicate how the glphy should be rendered (e.g. the foreground and background color).

Color is supported on all platforms, including Windows, Mac, and Linux. The default colors are 24-bit RGB colors, but the library will gracefully degrade to 16-colors if the terminal does not support 24-bit color, and black and white if the terminal does not support 16-colors.

View Drawing API

A View will typically draw text when the OnDrawContent is called (or the DrawContent event is received).

Outputting unformatted text involves:

a) Moving the draw cursor using the Move API. b) Setting the attributes using SetAttribute. c) Outputting glyphs by calling AddRune or AddStr.

Outputting formatted text involves:

a) Adding the text to a TextFormatter object. b) Setting formatting options, such as TextFormatter.TextAlignment. c) Calling TextFormatter.Draw.

Line drawing is accomplished using the LineCanvas API:

a) Add the lines via LineCanvas.Add. b) Either render the line canvas via LineCanvas.Draw or let the View do so automatically (which enables automatic line joining across Views).

Coordinate System for Drawing

The View draw APIs, including the OnDrawContent method, the DrawContent event, and the View.Move method, all take coordinates specified in Viewport-Relative coordinates. That is, 0, 0 is the top-left cell visible to the user.

See Layout for more details of the Terminal.Gui coordinate system.

Cell

The Cell class represents a single cell on the screen. It contains a character and an attribute. The character is of type Rune and the attribute is of type Attribute.

Cell is not exposed directly to the developer. Instead, the ConsoleDriver classes manage the Cell array that represents the screen.

To draw a Cell to the screen, use View.Move to specify the row and column coordinates and then use the View.AddRune method to draw a single glyph. To draw a string, use View.AddStr.

Unicode

Terminal.Gui supports the full range of Unicode/wide characters. This includes emoji, CJK characters, and other wide characters. For Unicode characters that require more than one cell, AddRune and the ConsoleDriver automatically manage the cells. Extension methods to Rune are provided to determine if a Rune is a wide character and to get the width of a Rune.

See the Character Map sample app in the UI Catalog for examples of Unicode characters.

Attribute

The Attribute class represents the formatting attributes of a Cell. It exposes properties for the foreground and background colors. The foreground and background colors are of type Color. In the future, it will expose properties for bold, underline, and other formatting attributes.

Color

The Color class represents a color. It provides automatic mapping between the legacy 4-bit (16-color) system and 24-bit colors. It contains properties for the red, green, and blue components of the color. The red, green, and blue components are of type byte. The Color class also contains a static property for each of the 16 ANSI colors.

Color Schemes

Terminal.Gui supports named collections of colors called ColorSchemes. Three built-in color schemes are provided: "Default", "Dark", and "Light". Additional color schemes can be defined via [Configuration Manager]().

Color schemes support defining colors for various states of a View. The following states are supported:

• Normal - The color of normal text.
• HotNormal - The color of text indicating a [Hotkey]().
• Focus - The color of text that indicates the view has focus.
• HotFocus - The color of text indicating a hot key, when the view has focus.
• Disabled - The state of a view when it is disabled.

Change the colors of a view by setting the View.ColorScheme property.

Text Formatting

Terminal.Gui supports text formatting using the [TextFormatter]() class. The TextFormatter class provides methods for formatting text using the following formatting options:

• Horizontal Alignment - Left, Center, Right
• Vertical Alignment - Top, Middle, Bottom
• Word Wrap - Enabled or Disabled
• Formatting Hot Keys

Glyphs

Terminal.Gui supports rendering glyphs using the Glyph class. The Glyph class represents a single glyph. It contains a character and an attribute. The character is of type Rune and the attribute is of type Attribute. A set of static properties are provided for the standard glyphs used for standard views (e.g. the default indicator for Button) and line drawing (e.g. LineCanvas).

Line Drawing

Terminal.Gui supports drawing lines and shapes using box-drawing glyphs. The LineCanvas class provides auto join, a smart TUI drawing system that automatically selects the correct line/box drawing glyphs for intersections making drawing complex shapes easy. See Line Canvas for details. The Snake and Line Drawing Scenarios in the UI Catalog sample app are both examples of the power of LineCanvas.

Thickness

Describes the thickness of a frame around a rectangle. The thickness is specified for each side of the rectangle using a Thickness object. The Thickness object contains properties for the left, top, right, and bottom thickness. The Adornment class uses Thickness to support drawing the frame around a view. The View class contains three Adornment-dervied properties:

• View.Margin.$2 - The space between the view and its peers (other views at the same level in the view hierarchy).
• View.Border.$2 - The space between the view and its Padding. This is where the frame, title, and other "Adornments" are drawn.
• View.Padding.$2 - The space between the view and its content. This is where the text, images, and other content is drawn. The inner rectangle of Padding is the Bounds of a view.

See View for details.