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scrollPosition.go
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scrollPosition.go
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package m
import "fmt"
// Please create using newScrollPosition(name)
type scrollPosition struct {
internalDontTouch scrollPositionInternal
}
func newScrollPosition(name string) scrollPosition {
if len(name) == 0 {
panic("Non-empty name required")
}
return scrollPosition{
internalDontTouch: scrollPositionInternal{
name: name,
},
}
}
type scrollPositionInternal struct {
// Line number in the input stream
lineNumberOneBased int
// Scroll this many screen lines before rendering. Can be negative.
deltaScreenLines int
name string
canonicalizing bool
canonical scrollPositionCanonical
}
// If any of these change, we have to recompute the scrollPositionInternal values
type scrollPositionCanonical struct {
width int // From pager
height int // From pager
showLineNumbers bool // From pager
showStatusBar bool // From pager
wrapLongLines bool // From pager
lineNumberOneBased int // From scrollPositionInternal
deltaScreenLines int // From scrollPositionInternal
}
func canonicalFromPager(pager *Pager) scrollPositionCanonical {
width, height := pager.screen.Size()
return scrollPositionCanonical{
width: width,
height: height,
showLineNumbers: pager.ShowLineNumbers,
showStatusBar: pager.ShowStatusBar,
wrapLongLines: pager.WrapLongLines,
lineNumberOneBased: pager.scrollPosition.internalDontTouch.lineNumberOneBased,
deltaScreenLines: pager.scrollPosition.internalDontTouch.deltaScreenLines,
}
}
// Create a new position, scrolled towards the end of the file
func (s scrollPosition) PreviousLine(scrollDistance int) scrollPosition {
return scrollPosition{
internalDontTouch: scrollPositionInternal{
name: s.internalDontTouch.name,
lineNumberOneBased: s.internalDontTouch.lineNumberOneBased,
deltaScreenLines: s.internalDontTouch.deltaScreenLines - scrollDistance,
},
}
}
// Create a new position, scrolled towards the end of the file
func (s scrollPosition) NextLine(scrollDistance int) scrollPosition {
return scrollPosition{
internalDontTouch: scrollPositionInternal{
name: s.internalDontTouch.name,
lineNumberOneBased: s.internalDontTouch.lineNumberOneBased,
deltaScreenLines: s.internalDontTouch.deltaScreenLines + scrollDistance,
},
}
}
// Create a new position, scrolled to the given line number
func NewScrollPositionFromLineNumberOneBased(lineNumberOneBased int, source string) scrollPosition {
return scrollPosition{
internalDontTouch: scrollPositionInternal{
name: source,
lineNumberOneBased: lineNumberOneBased,
deltaScreenLines: 0,
},
}
}
// Move towards the top until deltaScreenLines is not negative any more
func (si *scrollPositionInternal) handleNegativeDeltaScreenLines(pager *Pager) {
for si.lineNumberOneBased > 1 && si.deltaScreenLines < 0 {
// Render the previous line
previousLine := pager.reader.GetLine(si.lineNumberOneBased - 1)
previousSubLines := pager.renderLine(previousLine, 0)
// Adjust lineNumberOneBased and deltaScreenLines to move up into the
// previous screen line
si.lineNumberOneBased--
si.deltaScreenLines += len(previousSubLines)
}
if si.lineNumberOneBased <= 1 && si.deltaScreenLines <= 0 {
// Don't go above the top line
si.lineNumberOneBased = 1
si.deltaScreenLines = 0
}
}
// Move towards the bottom until deltaScreenLines is within range of the
// rendering of the current line.
//
// This method will not do any screen-height based clipping, so it could be that
// the position is too far down to display after this returns.
func (si *scrollPositionInternal) handlePositiveDeltaScreenLines(pager *Pager) {
for {
line := pager.reader.GetLine(si.lineNumberOneBased)
if line == nil {
// Out of bounds downwards, get the last line...
si.lineNumberOneBased = pager.reader.GetLineCount()
line = pager.reader.GetLine(si.lineNumberOneBased)
if line == nil {
panic(fmt.Errorf("Last line is nil"))
}
subLines := len(pager.renderLine(line, 0))
// ... and go to the bottom of that.
si.deltaScreenLines = subLines - 1
return
}
subLines := len(pager.renderLine(line, 0))
if si.deltaScreenLines < subLines {
// Sublines are within bounds!
return
}
si.lineNumberOneBased++
si.deltaScreenLines -= subLines
}
}
// This method assumes si contains a canonical position
func (si *scrollPositionInternal) emptyBottomLinesCount(pager *Pager) int {
_, height := pager.screen.Size()
unclaimedViewportLines := height - 1
if !pager.ShowStatusBar {
unclaimedViewportLines = height
}
// Start counting where the current input line begins
unclaimedViewportLines += si.deltaScreenLines
lineNumberOneBased := si.lineNumberOneBased
for {
line := pager.reader.GetLine(lineNumberOneBased)
if line == nil {
// No more lines!
break
}
subLines := len(pager.renderLine(line, 0))
unclaimedViewportLines -= subLines
if unclaimedViewportLines <= 0 {
return 0
}
// Move to the next line
lineNumberOneBased += 1
}
return unclaimedViewportLines
}
func (si *scrollPositionInternal) isCanonical(pager *Pager) bool {
if si.canonical.lineNumberOneBased == 0 {
// Awaiting initial lines from the reader
return false
}
if si.canonical == canonicalFromPager(pager) {
return true
}
return false
}
// Only to be called from the scrollPosition getters!!
//
// Canonicalize the scroll position vs the given pager. A canonical position can
// just be displayed on screen, it has been clipped both towards the top and
// bottom of the screen, taking into account the screen height.
func (si *scrollPositionInternal) canonicalize(pager *Pager) {
if si.isCanonical(pager) {
return
}
if si.canonicalizing {
panic(fmt.Errorf("Scroll position canonicalize() called recursively for %s", si.name))
}
si.canonicalizing = true
defer func() {
si.canonical = canonicalFromPager(pager)
si.canonicalizing = false
}()
if pager.reader.GetLineCount() == 0 {
si.lineNumberOneBased = 0
si.deltaScreenLines = 0
return
}
si.handleNegativeDeltaScreenLines(pager)
si.handlePositiveDeltaScreenLines(pager)
emptyBottomLinesCount := si.emptyBottomLinesCount(pager)
if emptyBottomLinesCount > 0 {
// First, adjust deltaScreenLines to get us to the top
si.deltaScreenLines -= emptyBottomLinesCount
// Then, actually go up that many lines
si.handleNegativeDeltaScreenLines(pager)
}
}
func scrollPositionFromLineNumber(name string, lineNumberOneBased int) *scrollPosition {
return &scrollPosition{
internalDontTouch: scrollPositionInternal{
name: name,
lineNumberOneBased: lineNumberOneBased,
},
}
}
// Line number in the input stream, or 0 if nothing has been read
func (p *Pager) lineNumberOneBased() int {
p.scrollPosition.internalDontTouch.canonicalize(p)
return p.scrollPosition.internalDontTouch.lineNumberOneBased
}
// Line number in the input stream, or 0 if nothing has been read
func (sp *scrollPosition) lineNumberOneBased(pager *Pager) int {
sp.internalDontTouch.canonicalize(pager)
return sp.internalDontTouch.lineNumberOneBased
}
// Scroll this many screen lines before rendering
//
// Always >= 0.
func (p *Pager) deltaScreenLines() int {
p.scrollPosition.internalDontTouch.canonicalize(p)
return p.scrollPosition.internalDontTouch.deltaScreenLines
}
// Scroll this many screen lines before rendering
//
// Always >= 0.
func (sp *scrollPosition) deltaScreenLines(pager *Pager) int {
sp.internalDontTouch.canonicalize(pager)
return sp.internalDontTouch.deltaScreenLines
}
func (p *Pager) scrollToEnd() {
inputLineCount := p.reader.GetLineCount()
if inputLineCount == 0 {
return
}
lastInputLineNumberOneBased := inputLineCount
lastInputLine := p.reader.GetLine(lastInputLineNumberOneBased)
p.scrollPosition.internalDontTouch.lineNumberOneBased = lastInputLineNumberOneBased
// Scroll down enough. We know for sure the last line won't wrap into more
// lines than the number of characters it contains.
p.scrollPosition.internalDontTouch.deltaScreenLines = len(lastInputLine.raw)
p.Following = true
}
// Can be either because Pager.scrollToEnd() was just called or because the user
// has pressed the down arrow enough times.
func (p *Pager) isScrolledToEnd() bool {
inputLineCount := p.reader.GetLineCount()
if inputLineCount == 0 {
// No lines available, which means we can't scroll any further down
return true
}
lastInputLineNumberOneBased := inputLineCount
visibleLines, _ := p.renderLines()
lastVisibleLine := visibleLines[len(visibleLines)-1]
if lastVisibleLine.inputLineOneBased != lastInputLineNumberOneBased {
// Last input line is not on the screen
return false
}
// Last line is on screen, now we need to figure out whether we can see all
// of it
lastInputLine := p.reader.GetLine(lastInputLineNumberOneBased)
lastInputLineRendered := p.renderLine(lastInputLine, lastInputLineNumberOneBased)
lastRenderedSubLine := lastInputLineRendered[len(lastInputLineRendered)-1]
// If the last visible subline is the same as the last possible subline then
// we're at the bottom
return lastVisibleLine.wrapIndex == lastRenderedSubLine.wrapIndex
}
// Returns nil if there are no lines
func (p *Pager) getLastVisiblePosition() *scrollPosition {
renderedLines, _ := p.renderLines()
if len(renderedLines) == 0 {
return nil
}
lastRenderedLine := renderedLines[len(renderedLines)-1]
return &scrollPosition{
internalDontTouch: scrollPositionInternal{
name: "Last Visible Position",
lineNumberOneBased: lastRenderedLine.inputLineOneBased,
deltaScreenLines: lastRenderedLine.wrapIndex,
},
}
}
func (p *Pager) numberPrefixLength() int {
// This method used to live in screenLines.go, but I moved it here because
// it touches scroll position internals.
if !p.ShowLineNumbers {
return 0
}
_, height := p.screen.Size()
contentHeight := height - 1 // Full screen height minus the status bar
maxPossibleLineNumber := p.reader.GetLineCount()
// This is an approximation assuming we don't do any wrapping. Finding the
// real answer while wrapping requires rendering, which requires the real
// answer and so on, so we do an approximation here to save us from
// recursion.
//
// Let's improve on demand.
maxVisibleLineNumber := (p.scrollPosition.internalDontTouch.lineNumberOneBased +
p.scrollPosition.internalDontTouch.deltaScreenLines + contentHeight - 1)
if maxVisibleLineNumber > maxPossibleLineNumber {
maxVisibleLineNumber = maxPossibleLineNumber
}
// Count the length of the last line number
numberPrefixLength := len(formatNumber(uint(maxVisibleLineNumber))) + 1
if numberPrefixLength < 4 {
// 4 = space for 3 digits followed by one whitespace
//
// https://github.com/walles/moar/issues/38
numberPrefixLength = 4
}
return numberPrefixLength
}