tui/views/view_scroll.go

package views

import (
	"math"

	"git.milar.in/milarin/buf2d"
	"git.milar.in/milarin/gmath"
	"git.milar.in/milarin/tui"
	"github.com/gdamore/tcell"
)

// ScrollView is a tui.View which can hold an arbitrary large view.
// If the sub view does not fit into its bounds, scroll bars will be shown
type ScrollView struct {
	tui.WrapperTmpl
	buf *tui.ViewBuffer

	width, height int

	verticalScrollOffset   int
	horizontalScrollOffset int
}

var _ tui.Wrapper = &ScrollView{}

func NewScrollView(view tui.View) *ScrollView {
	v := new(ScrollView)
	v.SetView(view)
	return v
}

func (v *ScrollView) Draw(buf *tui.ViewBuffer) {
	v.ViewTmpl.Draw(buf)

	w, h := v.View().Layout()

	if v.buf == nil || v.buf.Width() != w || v.buf.Height() != h {
		v.buf = buf2d.NewBuffer(w, h, tui.DefaultRune)
	}

	v.Scroll(0, 0) // limit scroll offset boundaries
	v.View().Draw(v.buf)

	scrollH, scrollV := v.determineViewportSize(buf)
	copyBufferWidth, copyBufferHeight := 0, 0

	if scrollH {
		copyBufferWidth = v.width
	} else {
		copyBufferWidth = v.buf.Width()
	}

	if scrollV {
		copyBufferHeight = v.height
	} else {
		copyBufferHeight = v.buf.Height()
	}

	// copy buffer
	for x := 0; x < copyBufferWidth; x++ {
		for y := 0; y < copyBufferHeight; y++ {
			buf.Set(x, y, v.buf.Get(v.horizontalScrollOffset+x, v.verticalScrollOffset+y))
		}
	}

	scrollVHeight := int(float64(buf.Height()) / float64(v.buf.Height()) * float64(v.height))
	scrollVStart := int(math.Ceil(float64(v.verticalScrollOffset) / float64(v.buf.Height()) * float64(v.height)))

	scrollHStart := int(float64(v.horizontalScrollOffset) / float64(v.buf.Width()) * float64(v.width))
	scrollHWidth := int(math.Ceil(float64(buf.Width()) / float64(v.buf.Width()) * float64(v.width)))

	// guarantee minimum scroll bar thumb size of 1 TODO inaccurate for small scales
	if scrollVHeight <= 0 {
		scrollVHeight = 1
		if scrollVStart >= v.height {
			scrollVStart = v.height - 1
		}
	}
	if scrollHWidth <= 0 {
		scrollHWidth = 1
		if scrollHStart >= v.width {
			scrollHStart = v.width - 1
		}
	}

	// vertical scrollbar
	if scrollV {
		for y := 0; y < v.height; y++ {
			var style tcell.Style
			if y >= scrollVStart && y < scrollVStart+scrollVHeight {
				style = tui.StyleDefault.Background(tcell.ColorWhite)
			} else {
				style = tui.StyleDefault.Background(tcell.ColorDarkSlateGray)
			}
			buf.Set(v.width, y, tui.Rune{Rn: ' ', Style: style})
		}
	}

	// horizontal scrollbar
	if scrollH {
		for x := 0; x < v.width; x++ {
			var style tcell.Style
			if x >= scrollHStart && x < scrollHStart+scrollHWidth {
				style = tui.StyleDefault.Background(tcell.ColorWhite)
			} else {
				style = tui.StyleDefault.Background(tcell.ColorDarkSlateGray)
			}
			buf.Set(x, v.height, tui.Rune{Rn: ' ', Style: style})
		}
	}
}

func (v *ScrollView) Layout() (prefWidth, prefHeight int) {
	return -1, -1
}

func (v *ScrollView) Scroll(verticalOffset, horizontalOffset int) {
	if v.buf != nil {
		v.verticalScrollOffset = gmath.Clamp(v.verticalScrollOffset+verticalOffset, 0, gmath.Max(v.buf.Height()-v.height, 0))
		v.horizontalScrollOffset = gmath.Clamp(v.horizontalScrollOffset+horizontalOffset, 0, gmath.Max(v.buf.Width()-v.width, 0))
	} else {
		v.verticalScrollOffset = v.verticalScrollOffset + verticalOffset
		v.horizontalScrollOffset = v.horizontalScrollOffset + horizontalOffset
	}
}

func (v *ScrollView) determineViewportSize(buf *tui.ViewBuffer) (scrollbarH, scrollbarV bool) {
	v.width, v.height = buf.Width()-1, buf.Height()-1
	scrollbarV = v.buf.Height() > v.height
	scrollbarH = v.buf.Width() > v.width

	if scrollbarV && !scrollbarH {
		v.height++
		scrollbarV = v.buf.Height() > v.height
	}

	if !scrollbarV && scrollbarH {
		v.width++
		scrollbarH = v.buf.Width() > v.width
	}

	return
}