zntg/ui/overflow.go

package ui

import (
	"image/color"

	"opslag.de/schobers/geom"
)

type overflow struct {
	Proxy

	Background color.Color

	barWidth float32
	desired  geom.PointF32
	bounds   geom.RectangleF32
	buffer   Image

	hor *Scrollbar
	ver *Scrollbar
}

func Overflow(content Control) Control {
	return OverflowBackground(content, nil)
}

func OverflowBackground(content Control, back color.Color) Control {
	var o = &overflow{Proxy: Proxy{Content: content}, Background: back}
	o.hor = BuildScrollbar(OrientationHorizontal, func(*Scrollbar) {})
	o.ver = BuildScrollbar(OrientationVertical, func(*Scrollbar) {})
	return o
}

func (o *overflow) shouldScroll(bounds geom.RectangleF32) (hor bool, ver bool) {
	var scroll = func(need, actual float32) bool {
		return !geom.IsNaN32(need) && need > actual
	}
	var size = o.desired
	hor = scroll(size.X, bounds.Dx())
	ver = scroll(size.Y, bounds.Dy())
	if ver && !hor {
		hor = scroll(size.X+o.barWidth, bounds.Dx())
	}
	if hor && !ver {
		ver = scroll(size.Y+o.barWidth, bounds.Dy())
	}
	return
}

func (o *overflow) doOnVisibleBars(fn func(bar *Scrollbar)) {
	hor, ver := o.shouldScroll(o.bounds)
	if hor {
		fn(o.hor)
	}
	if ver {
		fn(o.ver)
	}
}

func (o *overflow) Arrange(ctx Context, bounds geom.RectangleF32, offset geom.PointF32) {
	o.barWidth = ctx.Style().Dimensions.ScrollbarWidth
	o.desired = o.Content.DesiredSize(ctx)
	o.bounds = bounds

	var hor, ver = o.shouldScroll(bounds)
	var contentX, contentY float32 = 0, 0
	var contentW, contentH = bounds.Dx(), bounds.Dy()
	if hor {
		contentX -= o.hor.Offset
		contentH = geom.Max32(0, contentH-o.barWidth)
	}
	if ver {
		contentY -= o.ver.Offset
		contentW = geom.Max32(0, contentW-o.barWidth)
	}
	o.Content.Arrange(ctx, geom.RectF32(contentX, contentY, contentW, contentH), offset.Add(bounds.Min))
	if hor {
		o.hor.Content = o.desired.X
		o.hor.Arrange(ctx, geom.RectF32(bounds.Min.X, bounds.Min.Y+contentH, bounds.Min.X+contentW, bounds.Max.Y), offset)
	}
	if ver {
		o.ver.Content = o.desired.Y
		o.ver.Arrange(ctx, geom.RectF32(bounds.Min.X+contentW, bounds.Min.Y, bounds.Max.X, bounds.Max.Y), offset)
	}
}

func (o *overflow) Handle(ctx Context, e Event) {
	hor, ver := o.shouldScroll(o.bounds)
	if hor {
		o.hor.Handle(ctx, e)
	}
	if ver {
		o.ver.Handle(ctx, e)
	}
	o.Content.Handle(ctx, e)
}

func (o *overflow) Render(ctx Context) {
	var renderer = ctx.Renderer()

	if o.Background != nil {
		ctx.Renderer().FillRectangle(o.bounds, o.Background)
	}

	var content = o.Content.Bounds()
	if o.buffer == nil || o.buffer.Width() != content.Dx() || o.buffer.Height() != content.Dy() {
		if o.buffer != nil {
			o.buffer.Destroy()
			o.buffer = nil
		}
		buffer, err := renderer.CreateImageSize(content.Dx(), content.Dy())
		if err != nil {
			panic(err)
		}
		o.buffer = buffer
	}

	target := renderer.Target()
	renderer.RenderTo(o.buffer)
	renderer.Clear(color.Transparent)
	o.Content.Render(ctx)
	renderer.RenderTo(target)
	renderer.DrawImage(o.bounds.Min, o.buffer)

	o.doOnVisibleBars(func(bar *Scrollbar) {
		bar.Render(ctx)
	})
}