Brick.Widgets.Core

This module provides the core widget combinators and rendering routines. Everything this library does is in terms of these basic primitives.

Basic rendering primitives

emptyWidget :: Widget

The empty widget.

raw :: Image -> Widget

Build a widget directly from a raw Vty image.

txt :: Text -> Widget

Build a widget from a one-line Text value. Behaves the same as str.

str :: String -> Widget

Build a widget from a String. Breaks newlines up and space-pads short lines out to the length of the longest line.

fill :: Char -> Widget

Fill all available space with the specified character. Grows both horizontally and vertically.

Padding

padLeft :: Padding -> Widget -> Widget

Pad the specified widget on the left. If max padding is used, this grows greedily horizontally; otherwise it defers to the padded widget.

padRight :: Padding -> Widget -> Widget

Pad the specified widget on the right. If max padding is used, this grows greedily horizontally; otherwise it defers to the padded widget.

padTop :: Padding -> Widget -> Widget

Pad the specified widget on the top. If max padding is used, this grows greedily vertically; otherwise it defers to the padded widget.

padBottom :: Padding -> Widget -> Widget

Pad the specified widget on the bottom. If max padding is used, this grows greedily vertically; otherwise it defers to the padded widget.

padLeftRight :: Int -> Widget -> Widget

Pad a widget on the left and right. Defers to the padded widget for growth policy.

padTopBottom :: Int -> Widget -> Widget

Pad a widget on the top and bottom. Defers to the padded widget for growth policy.

padAll :: Int -> Widget -> Widget

Pad a widget on all sides. Defers to the padded widget for growth policy.

Box layout

(<=>)

Arguments

:: Widget

Top

-> Widget

Bottom

-> Widget

Vertical box layout: put the specified widgets one above the other in the specified order. Defers growth policies to the growth policies of both widgets. This operator is a binary version of vBox.

(<+>)

Arguments

:: Widget

Left

-> Widget

Right

-> Widget

Horizontal box layout: put the specified widgets next to each other in the specified order. Defers growth policies to the growth policies of both widgets. This operator is a binary version of hBox.

hBox :: [Widget] -> Widget

Horizontal box layout: put the specified widgets next to each other in the specified order (leftmost first). Defers growth policies to the growth policies of the contained widgets (if any are greedy, so is the box).

vBox :: [Widget] -> Widget

Vertical box layout: put the specified widgets one above the other in the specified order (uppermost first). Defers growth policies to the growth policies of the contained widgets (if any are greedy, so is the box).

Limits

hLimit :: Int -> Widget -> Widget

Limit the space available to the specified widget to the specified number of columns. This is important for constraining the horizontal growth of otherwise-greedy widgets. This is non-greedy horizontally and defers to the limited widget vertically.

vLimit :: Int -> Widget -> Widget

Limit the space available to the specified widget to the specified number of rows. This is important for constraining the vertical growth of otherwise-greedy widgets. This is non-greedy vertically and defers to the limited widget horizontally.

Attribute management

withDefAttr :: AttrName -> Widget -> Widget

Update the attribute map while rendering the specified widget: set its new default attribute to the one that we get by looking up the specified attribute name in the map.

withAttr :: AttrName -> Widget -> Widget

When drawing the specified widget, set the current attribute used for drawing to the one with the specified name. Note that the widget may use further calls to withAttr to override this; if you really want to prevent that, use forceAttr. Attributes used this way still get merged hierarchically and still fall back to the attribute map's default attribute. If you want to change the default attribute, use withDefAttr.

forceAttr :: AttrName -> Widget -> Widget

When rendering the specified widget, force all attribute lookups in the attribute map to use the value currently assigned to the specified attribute name.

updateAttrMap :: (AttrMap -> AttrMap) -> Widget -> Widget

When rendering the specified widget, update the attribute map with the specified transformation.

Border style management

withBorderStyle :: BorderStyle -> Widget -> Widget

When rendering the specified widget, use the specified border style for any border rendering.

Cursor placement

showCursor :: Name -> Location -> Widget -> Widget

When rendering the specified widget, also register a cursor positioning request using the specified name and location.

Translation

translateBy :: Location -> Widget -> Widget

Translate the specified widget by the specified offset amount. Defers to the translated width for growth policy.

Cropping

cropLeftBy :: Int -> Widget -> Widget

Crop the specified widget on the left by the specified number of columns. Defers to the translated width for growth policy.

cropRightBy :: Int -> Widget -> Widget

Crop the specified widget on the right by the specified number of columns. Defers to the translated width for growth policy.

cropTopBy :: Int -> Widget -> Widget

Crop the specified widget on the top by the specified number of rows. Defers to the translated width for growth policy.

cropBottomBy :: Int -> Widget -> Widget

Crop the specified widget on the bottom by the specified number of rows. Defers to the translated width for growth policy.

Scrollable viewports

viewport

Arguments

:: Name

The name of the viewport (must be unique and stable for reliable behavior)

-> ViewportType

The type of viewport (indicates the permitted scrolling direction)

-> Widget

The widget to be rendered in the scrollable viewport

-> Widget

Render the specified widget in a named viewport with the specified type. This permits widgets to be scrolled without being scrolling-aware. To make the most use of viewports, the specified widget should use the visible combinator to make a "visibility request". This viewport combinator will then translate the resulting rendering to make the requested region visible. In addition, the EventM monad provides primitives to scroll viewports created by this function if visible is not what you want.

If a viewport receives more than one visibility request, then the visibility requests are merged with the inner visibility request taking preference. If a viewport receives more than one scrolling request from EventM, all are honored in the order in which they are received.

visible :: Widget -> Widget

Request that the specified widget be made visible when it is rendered inside a viewport. This permits widgets (whose sizes and positions cannot be known due to being embedded in arbitrary layouts) to make a request for a parent viewport to locate them and scroll enough to put them in view. This, together with viewport, is what makes the text editor and list widgets possible without making them deal with the details of scrolling state management.

This does nothing if not rendered in a viewport.

visibleRegion :: Location -> DisplayRegion -> Widget -> Widget

Similar to visible, request that a region (with the specified Location as its origin and DisplayRegion as its size) be made visible when it is rendered inside a viewport. The Location is relative to the specified widget's upper-left corner of (0, 0).

This does nothing if not rendered in a viewport.

unsafeLookupViewport :: Name -> RenderM (Maybe Viewport)

Given a name, obtain the viewport for that name by consulting the viewport map in the rendering monad. NOTE! Some care must be taken when calling this function, since it only returns useful values after the viewport in question has been rendered. If you call this function during rendering before a viewport has been rendered, you may get nothing or you may get a stale version of the viewport. This is because viewports are updated during rendering and the one you are interested in may not have been rendered yet. So if you want to use this, be sure you know what you are doing.

Adding offsets to cursor positions and visibility requests

addResultOffset :: Location -> Result -> Result

Add an offset to all cursor locations and visbility requests in the specified rendering result. This function is critical for maintaining correctness in the rendering results as they are processed successively by box layouts and other wrapping combinators, since calls to this function result in converting from widget-local coordinates to (ultimately) terminal-global ones so they can be used by other combinators. You should call this any time you render something and then translate it or otherwise offset it from its original origin.

Cropping results

cropToContext :: Widget -> Widget

After rendering the specified widget, crop its result image to the dimensions in the rendering context.