wehub-resource-sync
69 lines
2.2 KiB
Go
69 lines
2.2 KiB
Go
package gui
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import (
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"image"
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"gioui.org/gesture"
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"gioui.org/io/pointer"
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"gioui.org/layout"
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"gioui.org/op"
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"gioui.org/widget"
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"gioui.org/widget/material"
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)
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// ScrollRegion is the vertical scroll state for a manually drawn
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// column: wheel/gesture scrolling, a scrollbar, and animated jumps.
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// Offset is the pixel offset of the content top relative to the
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// viewport top, so it goes negative as the content scrolls up.
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type ScrollRegion struct {
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Offset float32
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Gesture gesture.Scroll
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Bar widget.Scrollbar
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Anim ScrollAnimation
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}
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// LayoutBar draws a vertical scrollbar at barX with the given width,
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// applies scrollbar drags and scroll gestures, and clamps the offset
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// so the viewport stays within [contentTop, contentBot].
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func (region *ScrollRegion) LayoutBar(gtx layout.Context, th *material.Theme, barX, barWidth int, contentTop, contentBot float32) {
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viewTop := -region.Offset
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viewBot := -region.Offset + float32(gtx.Constraints.Max.Y)
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stack := op.Offset(image.Pt(barX, 0)).Push(gtx.Ops)
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bgtx := gtx
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bgtx.Constraints = layout.Exact(image.Pt(barWidth, gtx.Constraints.Max.Y))
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material.Scrollbar(th, ®ion.Bar).Layout(bgtx, layout.Vertical,
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(viewTop-contentTop)/(contentBot-contentTop),
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(viewBot-contentTop)/(contentBot-contentTop),
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)
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stack.Pop()
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if distance := region.Bar.ScrollDistance(); distance != 0 {
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region.Offset -= distance * (contentBot - contentTop)
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}
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if distance := region.Gesture.Update(gtx.Metric, gtx.Source, gtx.Now, gesture.Vertical,
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pointer.ScrollRange{},
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pointer.ScrollRange{Min: -1000, Max: 1000},
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); distance != 0 {
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region.Offset -= float32(distance)
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}
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region.Clamp(gtx, contentTop, contentBot)
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}
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// Clamp keeps the viewport within the content, stopping any running
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// jump animation when it hits an edge.
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func (region *ScrollRegion) Clamp(gtx layout.Context, contentTop, contentBot float32) {
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if -region.Offset < contentTop {
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region.Offset = -contentTop
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region.Anim.Stop()
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}
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if -region.Offset+float32(gtx.Constraints.Max.Y) > contentBot {
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if contentBot < float32(gtx.Constraints.Max.Y) {
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region.Offset = -contentTop
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} else {
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region.Offset = float32(gtx.Constraints.Max.Y) - contentBot
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}
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region.Anim.Stop()
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}
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}
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