tess

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 Go to latest Published: Feb 3, 2026 License: MIT Imports: 8 Imported by: 0

README

tess

A layout engine in Go powered by Yoga.

// Create a root Node
root, err := tess.NewNode()
root.SetWidth(tess.Point(400))
root.SetHeight(tess.Point(300))
root.SetPadding(tess.Edges{All: tess.Point(20)})

// Add a child to the root Node
child, err := tess.NewNode()
child.SetWidth(tess.Percent(100))
child.SetHeight(tess.Point(150))
root.AppendChild(child)

// Compute the layout to get final positions and sizes
root.ComputeLayout(tess.Container{})

// Get computed layout for a child
layout := root.GetChild(0).GetLayout()
// Use these values to render your element on screen
layout.Left()
layout.Top()
layout.Width()
layout.Height()

Introduction

tess determines the position and size of UI element using browser-style flexbox and style attributes.

It can be used to build terminal UIs, game interfaces, PDF layouts, or anything else where you need flexible box-model positioning.

Core concepts

Nodes - are the building blocks of your layout tree. Each node represents a UI element that needs positioning and sizing.

Styles - controls how nodes behave (width, height, padding, flex direction, etc). Think CSS properties, but for any rendering system.

Layouts - contains the final calculated positions and sizes of nodes that you can use to render elements on screen.

Usage

Installation

go get github.com/AnatoleLucet/tess

Getting started

As a starter project, let's center a div node! (I know right!?)

package main

import (
	"fmt"

	"github.com/AnatoleLucet/tess"
)

func main() {
  // Create a 500x500 container with children aligned and justified to center
  root, err := tess.NewNode()
  root.SetWidth(tess.Point(500)) // Points are the base unit for all measurements (think pixels but with a scale factor applied)
  root.SetHeight(tess.Point(500))
  root.SetJustifyContent(tess.JustifyCenter)
  root.SetAlignItems(tess.AlignCenter)

  // Add a child of 200x200 to the container
  child, err := tess.NewNode()
  child.SetWidth(tess.Point(200))
  child.SetHeight(tess.Point(200))
  root.AppendChild(child)

  root.ComputeLayout(tess.Container{})

  layout := child.GetLayout()
  layout.Left() // 150 (child is centered!)
  layout.Top() // 150
}

Styling

Apply styles to nodes either by calling setter methods or passing a Style struct at creation.

root, err := tess.NewNode()
root.SetWidth(tess.Point(500))
root.SetHeight(tess.Point(500))
// or
root, err := tess.NewNode(&tess.Style{
  Width: tess.Point(500),
  Height: tess.Point(500),
})
Units

tess supports multiple unit types for sizing and positioning:

node.SetWidth(tess.Point(500))    // Absolute points
node.SetWidth(tess.Percent(100))  // Percentage of parent

node.SetWidth(tess.Auto())        // Automatic sizing
node.SetWidth(tess.Stretch())     // Stretch to fill
node.SetWidth(tess.MaxContent())  // Size to content
node.SetWidth(tess.FitContent())  // Fit content with constraints

node.SetWidth(tess.Undefined())   // Unset (use default behavior)
Edges
node.SetMargin(tess.Edges{Horizontal: tess.Point(10)})
node.SetMargin(tess.Edges{Start: tess.Point(10), End: tess.Point(10)})

node.SetPadding(tess.Edges{All: tess.Point(20)})

node.SetBorder(tess.Edges{Bottom: tess.Point(2)})

Computing layouts

After creating your node tree and setting styles, call ComputeLayout() to calculate positions and sizes:

err := root.ComputeLayout(tess.Container{})

The Container parameter specifies available space constraints. Pass an empty container to use the root node's dimensions, or specify width/height to constrain the layout:

err := root.ComputeLayout(tess.Container{
  Width: 1920,
  Height: 1080,

  Direction: tess.RTL, // You can also pass a direction for LTR support!
})

Call ComputeLayout() again whenever you change styles or the node tree to recalculate positions.

Configuring

Configs control global layout behavior. By default, all nodes share the same config.

config := tess.NewConfig()

// Controls pixel density for layout rounding - set to your display's DPI scale
config.SetPointScaleFactor(2.0) // e.g. 2x supersampling for high-DPI displays

// Apply config to a node (and optionally its children if they share this config)
root, err := tess.NewNode()
root.SetConfig(config)

TODOs

  • measurement callbacks
  • baseline callbacks
  • more examples

Credits

  • yoga for powering everything under the hood (so much little salt in this bad boy)

Documentation

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

This section is empty.

Types

type BoxSizingType 

type BoxSizingType int
const (
	ContentBox BoxSizingType = iota
	BorderBox
)

func (BoxSizingType) String 

func (t BoxSizingType) String() string

type Config 

type Config struct {
	// contains filtered or unexported fields
}

func NewConfig 

func NewConfig() *Config

func (*Config) GetPointScaleFactor 

func (c *Config) GetPointScaleFactor() float32

func (*Config) SetPointScaleFactor 

func (c *Config) SetPointScaleFactor(scale float32)

type Container 

type Container struct {
	Width     float32
	Height    float32
	Direction DirectionType
}

type DirectionType 

type DirectionType int
const (
	Inherit DirectionType = iota
	LTR
	RTL
)

func (DirectionType) String 

func (t DirectionType) String() string

type DisplayType 

type DisplayType int
const (
	Flex DisplayType = iota
	Contents
	None
)

func (DisplayType) String 

func (t DisplayType) String() string

type Edges 

type Edges struct {
	Top, Bottom, Left, Right Value
	Start, End               Value
	Horizontal, Vertical     Value
	All                      Value
}

Edges represents values for the edges of a box. Note: Start and End will always be prioritized over Left and Right when both are set.

type FlexAlign 

type FlexAlign int
const (
	AlignAuto FlexAlign = iota
	AlignStretch
	AlignBaseline
	AlignStart
	AlignEnd
	AlignCenter
	AlignSpaceBetween
	AlignSpaceAround
	AlignSpaceEvenly
)

func (FlexAlign) String 

func (a FlexAlign) String() string

type FlexDirection 

type FlexDirection int
const (
	Column FlexDirection = iota
	ColumnReverse
	Row
	RowReverse
)

func (FlexDirection) String 

func (a FlexDirection) String() string

type FlexJustify 

type FlexJustify int
const (
	JustifyStart FlexJustify = iota
	JustifyEnd
	JustifyCenter
	JustifySpaceBetween
	JustifySpaceAround
	JustifySpaceEvenly
)

func (FlexJustify) String 

func (a FlexJustify) String() string

type FlexWrap 

type FlexWrap int
const (
	NoWrap FlexWrap = iota
	Wrap
	WrapReverse
)

func (FlexWrap) String 

func (t FlexWrap) String() string

type Gap 

type Gap struct {
	Row    Value
	Column Value
	All    Value
}

Gap represents the gap values for rows and columns.

type Layout 

type Layout struct {
	// contains filtered or unexported fields
}

func (*Layout) AbsoluteBottom 

func (l *Layout) AbsoluteBottom() float32

func (*Layout) AbsoluteLeft 

func (l *Layout) AbsoluteLeft() float32

func (*Layout) AbsoluteRight 

func (l *Layout) AbsoluteRight() float32

func (*Layout) AbsoluteTop 

func (l *Layout) AbsoluteTop() float32

func (*Layout) Border 

func (l *Layout) Border() *LayoutEdges

func (*Layout) Bottom 

func (l *Layout) Bottom() float32

func (*Layout) Direction 

func (l *Layout) Direction() DirectionType

func (*Layout) HadOverflow 

func (l *Layout) HadOverflow() bool

func (*Layout) Height 

func (l *Layout) Height() float32

func (*Layout) Left 

func (l *Layout) Left() float32

func (*Layout) Margin 

func (l *Layout) Margin() *LayoutEdges

func (*Layout) Padding 

func (l *Layout) Padding() *LayoutEdges

func (*Layout) RawHeight 

func (l *Layout) RawHeight() float32

func (*Layout) RawWidth 

func (l *Layout) RawWidth() float32

func (*Layout) Right 

func (l *Layout) Right() float32

func (*Layout) Top 

func (l *Layout) Top() float32

func (*Layout) Width 

func (l *Layout) Width() float32

type LayoutEdges 

type LayoutEdges struct {
	// contains filtered or unexported fields
}

func (*LayoutEdges) Bottom 

func (e *LayoutEdges) Bottom() float32

func (*LayoutEdges) Left 

func (e *LayoutEdges) Left() float32

func (*LayoutEdges) Right 

func (e *LayoutEdges) Right() float32

func (*LayoutEdges) Top 

func (e *LayoutEdges) Top() float32

type MeasureFunc 

type MeasureFunc func(node *Node, width float32, widthMode MeasureMode, height float32, heightMode MeasureMode) Size

type MeasureMode 

type MeasureMode int
const (
	MeasureModeUndefined MeasureMode = iota
	MeasureModeExactly
	MeasureModeAtMost
)

func (MeasureMode) String 

func (m MeasureMode) String() string

type Node 

type Node struct {
	// contains filtered or unexported fields
}

func NewNode 

func NewNode(styles ...*Style) (*Node, error)

func (*Node) AppendChild 

func (n *Node) AppendChild(child *Node)

func (*Node) Apply 

func (n *Node) Apply(style *Style) error

Apply applies a Style to the node

func (*Node) Children 

func (n *Node) Children() iter.Seq[*Node]

func (*Node) Clone 

func (n *Node) Clone() *Node

func (*Node) CloneRecursive 

func (n *Node) CloneRecursive() *Node

func (*Node) ComputeLayout 

func (n *Node) ComputeLayout(container Container) error

func (*Node) Free 

func (n *Node) Free()

func (*Node) FreeRecursive 

func (n *Node) FreeRecursive()

func (*Node) GetAlignContent 

func (n *Node) GetAlignContent() FlexAlign

func (*Node) GetAlignItems 

func (n *Node) GetAlignItems() FlexAlign

func (*Node) GetAlignSelf 

func (n *Node) GetAlignSelf() FlexAlign

func (*Node) GetAspectRatio 

func (n *Node) GetAspectRatio() float32

func (*Node) GetBorder 

func (n *Node) GetBorder() *StyleEdges

func (*Node) GetBottom 

func (n *Node) GetBottom() Value

func (*Node) GetBoxSizing 

func (n *Node) GetBoxSizing() BoxSizingType

func (*Node) GetChild 

func (n *Node) GetChild(index int) *Node

func (*Node) GetChildCount 

func (n *Node) GetChildCount() int

func (*Node) GetConfig 

func (n *Node) GetConfig() *Config

func (*Node) GetDirection 

func (n *Node) GetDirection() DirectionType

func (*Node) GetDisplay 

func (n *Node) GetDisplay() DisplayType

func (*Node) GetFlexBasis 

func (n *Node) GetFlexBasis() Value

func (*Node) GetFlexDirection 

func (n *Node) GetFlexDirection() FlexDirection

func (*Node) GetFlexGrow 

func (n *Node) GetFlexGrow() float32

func (*Node) GetFlexShrink 

func (n *Node) GetFlexShrink() float32

func (*Node) GetFlexWrap 

func (n *Node) GetFlexWrap() FlexWrap

func (*Node) GetGap 

func (n *Node) GetGap() *StyleGap

func (*Node) GetHeight 

func (n *Node) GetHeight() Value

func (*Node) GetJustifyContent 

func (n *Node) GetJustifyContent() FlexJustify

func (*Node) GetLayout 

func (n *Node) GetLayout() *Layout

func (*Node) GetLeft 

func (n *Node) GetLeft() Value

func (*Node) GetMargin 

func (n *Node) GetMargin() *StyleEdges

func (*Node) GetMaxHeight 

func (n *Node) GetMaxHeight() Value

func (*Node) GetMaxWidth 

func (n *Node) GetMaxWidth() Value

func (*Node) GetMinHeight 

func (n *Node) GetMinHeight() Value

func (*Node) GetMinWidth 

func (n *Node) GetMinWidth() Value

func (*Node) GetNodeType 

func (n *Node) GetNodeType() NodeType

func (*Node) GetOverflow 

func (n *Node) GetOverflow() OverflowType

func (*Node) GetPadding 

func (n *Node) GetPadding() *StyleEdges

func (*Node) GetParent 

func (n *Node) GetParent() *Node

func (*Node) GetPosition 

func (n *Node) GetPosition() PositionType

func (*Node) GetRight 

func (n *Node) GetRight() Value

func (*Node) GetTop 

func (n *Node) GetTop() Value

func (*Node) GetWidth 

func (n *Node) GetWidth() Value

func (*Node) HasMeasureFunc 

func (n *Node) HasMeasureFunc() bool

func (*Node) HasNewLayout 

func (n *Node) HasNewLayout() bool

func (*Node) InsertChild 

func (n *Node) InsertChild(child *Node, index int)

func (*Node) IsDirty 

func (n *Node) IsDirty() bool

func (*Node) MarkDirty 

func (n *Node) MarkDirty()

MarkDirty marks the node as dirty. This will cause the next layout computation to recalculate this node and its children.

Note: this method should only be used for nodes with a custom measure function. Nodes without a measure function are marked dirty automatically when their style properties are changed.

func (*Node) RemoveAllChildren 

func (n *Node) RemoveAllChildren()

func (*Node) RemoveChild 

func (n *Node) RemoveChild(child *Node)

func (*Node) Reset 

func (n *Node) Reset()

func (*Node) SetAlignContent 

func (n *Node) SetAlignContent(align FlexAlign) error

func (*Node) SetAlignItems 

func (n *Node) SetAlignItems(align FlexAlign) error

func (*Node) SetAlignSelf 

func (n *Node) SetAlignSelf(align FlexAlign) error

func (*Node) SetAspectRatio 

func (n *Node) SetAspectRatio(aspectRatio float32) error

func (*Node) SetBorder 

func (n *Node) SetBorder(edges Edges) error

SetBorder sets the border widths for the node. Note: Borders can only be set in points.

func (*Node) SetBottom 

func (n *Node) SetBottom(bottom Value) error

func (*Node) SetBoxSizing 

func (n *Node) SetBoxSizing(boxSizing BoxSizingType) error

func (*Node) SetChildren 

func (n *Node) SetChildren(children []*Node)

func (*Node) SetConfig 

func (n *Node) SetConfig(config *Config)

func (*Node) SetDirection 

func (n *Node) SetDirection(direction DirectionType) error

func (*Node) SetDirty 

func (n *Node) SetDirty(dirty bool)

SetDirty directly sets the dirty flag on a node without propagating to parent.

func (*Node) SetDisplay 

func (n *Node) SetDisplay(display DisplayType) error

func (*Node) SetFlexBasis 

func (n *Node) SetFlexBasis(flexBasis Value) error

func (*Node) SetFlexDirection 

func (n *Node) SetFlexDirection(direction FlexDirection) error

func (*Node) SetFlexGrow 

func (n *Node) SetFlexGrow(flexGrow float32) error

func (*Node) SetFlexShrink 

func (n *Node) SetFlexShrink(flexShrink float32) error

func (*Node) SetFlexWrap 

func (n *Node) SetFlexWrap(wrap FlexWrap) error

func (*Node) SetGap 

func (n *Node) SetGap(gap Gap) error

SetGap sets the gap sizes for the node. Note: Gaps can be set in points or percent.

func (*Node) SetHasNewLayout 

func (n *Node) SetHasNewLayout(hasNewLayout bool)

func (*Node) SetHeight 

func (n *Node) SetHeight(height Value) error

func (*Node) SetJustifyContent 

func (n *Node) SetJustifyContent(justify FlexJustify) error

func (*Node) SetLeft 

func (n *Node) SetLeft(left Value) error

func (*Node) SetMargin 

func (n *Node) SetMargin(edges Edges) error

SetMargin sets the margin widths for the node. Note: Margins can be set in points, percent, or auto.

func (*Node) SetMaxHeight 

func (n *Node) SetMaxHeight(maxHeight Value) error

func (*Node) SetMaxWidth 

func (n *Node) SetMaxWidth(maxWidth Value) error

func (*Node) SetMeasureFunc 

func (n *Node) SetMeasureFunc(fn MeasureFunc)

func (*Node) SetMinHeight 

func (n *Node) SetMinHeight(minHeight Value) error

func (*Node) SetMinWidth 

func (n *Node) SetMinWidth(minWidth Value) error

func (*Node) SetNodeType 

func (n *Node) SetNodeType(nodeType NodeType) error

func (*Node) SetOverflow 

func (n *Node) SetOverflow(overflow OverflowType) error

func (*Node) SetPadding 

func (n *Node) SetPadding(edges Edges) error

SetPadding sets the padding for the node. Note: Padding can only be set in points or percent.

func (*Node) SetParent 

func (n *Node) SetParent(parent *Node)

func (*Node) SetPosition 

func (n *Node) SetPosition(position PositionType) error

func (*Node) SetRight 

func (n *Node) SetRight(right Value) error

func (*Node) SetTop 

func (n *Node) SetTop(top Value) error

func (*Node) SetWidth 

func (n *Node) SetWidth(width Value) error

func (*Node) Snapshot 

func (n *Node) Snapshot() *Node

Snapshot creates a deep clone of the node tree while preserving the dirty state. Unlike CloneRecursive which marks cloned nodes as dirty, Snapshot maintains the original dirty status, allowing cached layout computations to be reused.

func (*Node) UnsetMeasureFunc 

func (n *Node) UnsetMeasureFunc()

type NodeType 

type NodeType int
const (
	NodeTypeDefault NodeType = iota
	NodeTypeText
)

func (NodeType) String 

func (t NodeType) String() string

type OverflowType 

type OverflowType int
const (
	Visible OverflowType = iota
	Hidden
	Scroll
)

func (OverflowType) String 

func (t OverflowType) String() string

type PositionType 

type PositionType int
const (
	Static PositionType = iota
	Relative
	Absolute
)

func (PositionType) String 

func (t PositionType) String() string

type Size 

type Size struct {
	Width  float32
	Height float32
}

type Style 

type Style struct {
	// Display & Layout
	Display        DisplayType
	FlexDirection  FlexDirection
	JustifyContent FlexJustify
	AlignItems     FlexAlign
	AlignSelf      FlexAlign
	AlignContent   FlexAlign
	FlexWrap       FlexWrap
	Direction      DirectionType

	// Dimensions
	Width, Height       Value
	MinWidth, MinHeight Value
	MaxWidth, MaxHeight Value
	AspectRatio         float32

	// Spacing
	Padding Edges
	Margin  Edges
	Border  Edges
	Gap     Gap

	// Flex item properties
	FlexGrow   float32
	FlexShrink float32
	FlexBasis  Value

	// Positioning
	Position                 PositionType
	Top, Right, Bottom, Left Value

	// Overflow
	Overflow OverflowType

	// Box Sizing
	BoxSizing BoxSizingType
}

type StyleEdges 

type StyleEdges struct {
	// contains filtered or unexported fields
}

func (*StyleEdges) GetBottom 

func (e *StyleEdges) GetBottom() Value

func (*StyleEdges) GetEnd 

func (e *StyleEdges) GetEnd() Value

func (*StyleEdges) GetLeft 

func (e *StyleEdges) GetLeft() Value

func (*StyleEdges) GetRight 

func (e *StyleEdges) GetRight() Value

func (*StyleEdges) GetStart 

func (e *StyleEdges) GetStart() Value

func (*StyleEdges) GetTop 

func (e *StyleEdges) GetTop() Value

type StyleGap 

type StyleGap struct {
	// contains filtered or unexported fields
}

func (*StyleGap) GetAll 

func (g *StyleGap) GetAll() Value

func (*StyleGap) GetColumn 

func (g *StyleGap) GetColumn() Value

func (*StyleGap) GetRow 

func (g *StyleGap) GetRow() Value

type Unit 

type Unit int
const (
	UnitUndefined Unit = iota
	UnitPoint
	UnitPercent
	UnitMaxContent
	UnitFitContent
	UnitAuto
	UnitStretch
)

func (Unit) String 

func (u Unit) String() string

type Value 

type Value struct {
	// contains filtered or unexported fields
}

func Auto 

func Auto() Value

func FitContent 

func FitContent() Value

func MaxContent 

func MaxContent() Value

func Percent 

func Percent(percents float32) Value

func Point 

func Point(points float32) Value

func Stretch 

func Stretch() Value

func Undefined 

func Undefined() Value

func (Value) String 

func (v Value) String() string

func (Value) Unit 

func (v Value) Unit() Unit

func (Value) Value 

func (v Value) Value() float32

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