User interface toolkit for Go with support for SDL2 and HTML Canvas render targets.
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package ui
import (
// AbsolutePosition computes a widget's absolute X,Y position on the
// window on screen by crawling its parent widget tree.
func AbsolutePosition(w Widget) render.Point {
abs := w.Point()
var (
node = w
ok bool
for {
node, ok = node.Parent()
if !ok { // reached the top of the tree
return abs
// AbsoluteRect returns a Rect() offset with the absolute position.
// X and Y are the AbsolutePosition of the widget.
// W and H are the widget's width and height. (X,Y not added to them)
func AbsoluteRect(w Widget) render.Rect {
var (
P = AbsolutePosition(w)
R = w.Rect()
return render.Rect{
X: P.X,
Y: P.Y,
W: R.W,
H: R.H, // TODO: the Canvas in EditMode lets you draw pixels
// below the status bar if we do `+ R.Y` here.
// HasParent returns whether the target widget is a descendant of the parent.
// This scans the parents of the widget recursively until it finds a match.
func HasParent(w Widget, parent Widget) bool {
next, ok := w.Parent()
for ok {
if next == parent {
return true
next, ok = next.Parent()
return false
// widgetInFocusedWindow returns whether a widget (like a Button) is a
// descendant of a Window that is being Window Managed by Supervisor, and
// said window is in a Focused state.
// This is used by Supervisor to decide whether the widget should be given
// events or not: a widget in a non-focused window ignores events, so that a
// button in a "lower" window could not be clicked through a "higher" window
// that overlaps it.
func widgetInFocusedWindow(w Widget) (isManaged, isFocused bool) {
var node = w
for {
// Is the node a Window?
if window, ok := node.(*Window); ok {
return window.managed, window.Focused()
node, _ = node.Parent()
if node == nil {
return false, true // reached the root