node

type ContainerEmbed struct{ Embed }

type Embed struct {
	// Wrapper is the outer type that wraps (embeds) this type. It should not
	// be nil.
	Wrapper Node

	// Parent, FirstChild, LastChild, PrevSibling and NextSibling describe the
	// widget tree structure.
	//
	// These fields are exported to enable walking the node tree, but they
	// should not be modified directly. Instead, call the Insert and Remove
	// methods, which keeps the tree structure consistent.
	Parent, FirstChild, LastChild, PrevSibling, NextSibling *Embed

	// LayoutData is layout-specific data for this node. Its type is determined
	// by its parent node's type. For example, each child of a Flow may hold a
	// FlowLayoutData in this field.
	LayoutData interface{}

	// MeasuredSize is the widget's natural size, in pixels, as calculated by
	// the most recent Measure call.
	MeasuredSize image.Point

	// Rect is the widget's position and actual (as opposed to natural) size,
	// in pixels, as calculated by the most recent Layout call on its parent
	// node. A parent may lay out a child at a size different to its natural
	// size in order to satisfy a layout constraint, such as a row of buttons
	// expanding to fill a panel's width.
	//
	// The position (Rectangle.Min) is relative to its parent node. This is not
	// necessarily the same as relative to the screen's, window's or image
	// buffer's origin.
	Rect image.Rectangle

	// Marks are a bitfield of node state, such as whether it needs measure,
	// layout or paint.
	Marks Marks
}

type EventHandled bool

type LeafEmbed struct{ Embed }

type Marks uint32

type Node interface {
	// Wrappee returns the inner (embedded) type that is wrapped by this type.
	Wrappee() *Embed

	// Insert adds a node c as a child of this node. If nextSibling is nil, c
	// will be inserted at the end of this node's children. Otherwise, c will
	// be inserted such that its next sibling is nextSibling.
	//
	// It will panic if c already has a parent or siblings.
	Insert(c, nextSibling Node)

	// Remove removes a node c that is a child of this node. Afterwards, c will
	// have no parent and no siblings.
	//
	// It will panic if c's parent is not this node.
	Remove(c Node)

	// Measure sets this node's Embed.MeasuredSize to its natural size, taking
	// its children into account.
	//
	// Some nodes' natural height might depend on their imposed width, such as
	// a text widget word-wrapping its contents. The caller may provide hints
	// that the parent can override the child's natural size in the width,
	// height or both directions. A negative value means that there is no hint.
	// For example, a container might lay out its children to all have the same
	// width, and could pass that width as the widthHint argument.
	Measure(t *theme.Theme, widthHint, heightHint int)

	// Layout lays out this node (and its children), setting the Embed.Rect
	// fields of each child. This node's Embed.Rect field should have
	// previously been set during the parent node's layout.
	Layout(t *theme.Theme)

	// Paint paints this node (and its children). Painting is split into two
	// passes: a base pass and an effects pass. The effects pass is often a
	// no-op, and the bulk of the work is typically done in the base pass.
	//
	// The base pass paints onto an *image.RGBA pixel buffer and ancestor nodes
	// may choose to re-use the result. For example, re-painting a text widget
	// after scrolling may copy cached buffers at different offsets, instead of
	// painting the text's glyphs onto a fresh buffer. Similarly, animating the
	// scale and opacity of an overlay can re-use the buffer from a previous
	// base pass.
	//
	// The effects pass paints that part of the widget that can not or should
	// not be cached. For example, the border of a text widget shouldn't move
	// on the screen when that text widget is scrolled. The effects pass does
	// not have a destination RGBA pixel buffer, and is limited to what a
	// screen.Drawer provides: affine-transformed textures and uniform fills.
	//
	// TODO: app-specific OpenGL, if available, should be part of the effects
	// pass. Is that exposed via the screen.Drawer or by another mechanism?
	//
	// The Paint method may create base pass RGBA pixel buffers, by calling
	// ctx.Screen.NewBuffer. Many implementations won't, and instead assume
	// that PaintBase is recursively triggered by an ancestor node such as a
	// widget.Sheet. If it does create those RGBA pixel buffers, it is also
	// responsible for calling PaintBase on this node (and its children). In
	// any case, the Paint method should then paint any effects. Many widgets
	// will neither create their own buffers nor have any effects, so their
	// Paint methods will simply be the default implemention: do nothing except
	// call Paint on its children. As mentioned above, the bulk of the work is
	// typically done in PaintBase.
	//
	// origin is the parent widget's origin with respect to the ctx.Src2Dst
	// transformation matrix; this node's Embed.Rect.Add(origin) will be its
	// position and size in pre-transformed coordinate space.
	Paint(ctx *PaintContext, origin image.Point) error

	// PaintBase paints the base pass of this node (and its children) onto an
	// RGBA pixel buffer.
	//
	// origin is the parent widget's origin with respect to the ctx.Dst image's
	// origin; this node's Embed.Rect.Add(origin) will be its position and size
	// in ctx.Dst's coordinate space.
	PaintBase(ctx *PaintBaseContext, origin image.Point) error

	// Mark adds the given marks to this node. It calls OnChildMarked on its
	// parent if new marks were added.
	Mark(m Marks)

	// OnChildMarked handles a child being given new marks. By default, marks
	// are propagated up the node tree towards the root. For example, a child
	// being marked for needing paint will cause the parent being marked for
	// needing paint.
	OnChildMarked(child Node, newMarks Marks)

	// OnLifecycleEvent propagates a lifecycle event to a node (and its
	// children).
	OnLifecycleEvent(e lifecycle.Event)

	// OnInputEvent handles a key, mouse, touch or gesture event.
	//
	// origin is the parent widget's origin with respect to the event origin;
	// this node's Embed.Rect.Add(origin) will be its position and size in
	// event coordinate space.
	OnInputEvent(e interface{}, origin image.Point) EventHandled
}

type PaintBaseContext struct {
	Theme *theme.Theme
	Dst   *image.RGBA
}

type PaintContext struct {
	Theme   *theme.Theme
	Screen  screen.Screen
	Drawer  screen.Drawer
	Src2Dst f64.Aff3
}

type ShellEmbed struct{ Embed }