mirror of https://github.com/mum4k/termdash.git
Adding an object that tracks the scrolling state.
This commit is contained in:
Jakub Sobon
parent
7d14d2219f
commit
4c54b8a46e
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package text
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// scroll.go contains code that tracks the current scrolling position.
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import "math"
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// scrollTracker tracks the current scrolling position for the Text widget.
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// This is not thread safe.
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type scrollTracker struct {
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// scroll stores user requests to scroll up (negative) or down (positive).
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// E.g. -1 means up by one line and 2 means down by two lines.
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scroll int
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// scrollPage stores user requests to scroll up (negative) or down
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// (positive) by a page of content. E.g. -1 means up by one page and 2
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// means down by two pages.
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scrollPage int
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// first tracks the first line that will be printed.
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first int
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// state is the state of the scrolling FSM.
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state rollState
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}
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// newScrollTracker returns a new scroll tracker.
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func newScrollTracker(opts *options) *scrollTracker {
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if opts.rollContent {
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return &scrollTracker{state: rollToEnd}
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}
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return &scrollTracker{state: rollingDisabled}
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}
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// upOneLine processes a user request to scroll up by one line.
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func (st *scrollTracker) upOneLine() {
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st.scroll--
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}
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// downOneLine processes a user request to scroll down by one line.
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func (st *scrollTracker) downOneLine() {
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st.scroll++
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}
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// upOnePage processes a user request to scroll up by one page.
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func (st *scrollTracker) upOnePage() {
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st.scrollPage--
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}
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// downOnePage processes a user request to scroll down by one page.
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func (st *scrollTracker) downOnePage() {
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st.scrollPage++
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}
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// doScroll processes any outstanding scroll requests and calculates the
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// resulting first line.
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func (st *scrollTracker) doScroll(lines, height int) int {
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first := st.first + st.scroll + st.scrollPage*height
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st.scroll = 0
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st.scrollPage = 0
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return normalizeScroll(first, lines, height)
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}
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// firstLine returns the number of the first line that should be drawn on a
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// canvas of the specified height if there is the provided number of lines of
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// text.
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func (st *scrollTracker) firstLine(lines, height int) int {
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// Execute the scrolling FSM.
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st.state = st.state(st, lines, height)
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return st.first
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}
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// rollState is a state in the scrolling FSM.
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type rollState func(st *scrollTracker, lines, height int) rollState
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// rollingDisabled is a state where content rolling was disabled by the
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// configuration of the Text widget.
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func rollingDisabled(st *scrollTracker, lines, height int) rollState {
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st.first = st.doScroll(lines, height)
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return rollingDisabled
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}
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// rollToEnd is a state in which the last line of the content is always
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// visible. When new content arrives, it is rolled upwards.
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func rollToEnd(st *scrollTracker, lines, height int) rollState {
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// If the user didn't scroll, just roll the content so that the last line
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// is visible.
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if st.scroll == 0 && st.scrollPage == 0 {
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st.first = normalizeScroll(math.MaxUint32, lines, height)
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return rollToEnd
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}
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st.first = st.doScroll(lines, height)
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if lastLineVisible(st.first, lines, height) {
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return rollToEnd
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}
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return rollingPaused
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}
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// rollingPaused is a state in which the user scrolled up and made the last
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// line scroll out of the view, so the content rolling is paused.
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func rollingPaused(st *scrollTracker, lines, height int) rollState {
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st.first = st.doScroll(lines, height)
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if lastLineVisible(st.first, lines, height) {
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return rollToEnd
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}
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return rollingPaused
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}
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// lastLineVisible returns true if the last line is visible given drawing that
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// starts from the first line, the number of lines and the height of the
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// canvas.
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func lastLineVisible(first, lines, height int) bool {
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return lines-first <= height
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}
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// normalizeScroll returns normalized position of the first line that should be
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// drawn when drawing the specified number of lines on a canvas with the
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// provided height.
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func normalizeScroll(first, lines, height int) int {
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if first < 0 || lines <= 0 || height <= 0 {
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return 0
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}
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if lines <= height {
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return 0 // Scrolling not necessary if the content fits.
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}
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max := lines - height
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if first > max {
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return max
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}
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return first
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}
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@ -0,0 +1,318 @@
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package text
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import (
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"testing"
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)
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func TestScrollTrackerNoContentRolling(t *testing.T) {
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tests := []struct {
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desc string
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lines int
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height int
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events func(*scrollTracker)
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want int
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}{
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{
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desc: "starts from the first line",
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lines: 2,
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height: 1,
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want: 0,
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},
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{
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desc: "user can scroll down by a line",
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lines: 2,
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height: 1,
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events: func(st *scrollTracker) {
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st.downOneLine()
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},
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want: 1,
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},
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{
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desc: "scroll down capped at the last line",
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lines: 2,
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height: 1,
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events: func(st *scrollTracker) {
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st.downOneLine()
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st.downOneLine()
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},
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want: 1,
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},
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{
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desc: "larger terminal, scroll down capped at the last line",
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lines: 4,
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height: 2,
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events: func(st *scrollTracker) {
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st.downOneLine()
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st.downOneLine()
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st.downOneLine()
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st.downOneLine()
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st.downOneLine()
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},
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want: 2,
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},
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{
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desc: "scroll up capped at the first line",
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lines: 2,
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height: 1,
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events: func(st *scrollTracker) {
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st.upOneLine()
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st.upOneLine()
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},
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want: 0,
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},
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{
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desc: "processes multiple scroll events",
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lines: 4,
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height: 2,
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events: func(st *scrollTracker) {
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st.downOneLine()
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st.downOneLine()
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st.upOneLine()
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},
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want: 1,
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},
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{
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desc: "scrolling down ignored when all content fits",
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lines: 2,
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height: 4,
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events: func(st *scrollTracker) {
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st.downOneLine()
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st.downOneLine()
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},
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want: 0,
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},
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{
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desc: "scrolls down by a page",
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lines: 6,
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height: 2,
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events: func(st *scrollTracker) {
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st.downOnePage()
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st.downOnePage()
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},
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want: 4,
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},
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{
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desc: "scrolling down by a page capped at the last line",
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lines: 6,
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height: 2,
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events: func(st *scrollTracker) {
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st.downOnePage()
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st.downOnePage()
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st.downOnePage()
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st.downOnePage()
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},
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want: 4,
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},
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{
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desc: "scrolling up by a page capped at the first line",
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lines: 6,
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height: 2,
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events: func(st *scrollTracker) {
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st.downOnePage()
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st.upOnePage()
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st.upOnePage()
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st.upOnePage()
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st.upOnePage()
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},
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want: 0,
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},
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{
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desc: "scrolling by lines and pages can be combined",
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lines: 8,
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height: 2,
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events: func(st *scrollTracker) {
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st.downOnePage() // first == 2
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st.upOneLine() // first = 1
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st.downOneLine() // first = 2
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st.downOneLine() // first = 3
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st.downOneLine() // first = 4
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st.downOneLine() // first = 5
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st.upOnePage() // first == 3
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},
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want: 3,
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},
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}
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for _, tc := range tests {
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t.Run(tc.desc, func(t *testing.T) {
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st := newScrollTracker(&options{})
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if tc.events != nil {
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tc.events(st)
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}
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got := st.firstLine(tc.lines, tc.height)
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if got != tc.want {
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t.Errorf("firstLine => got %d, want %d", got, tc.want)
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}
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})
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}
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}
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func TestScrollTrackerContentRolling(t *testing.T) {
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st := newScrollTracker(&options{rollContent: true})
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// All of these test cases act on the same instance of the scroll tracker.
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tests := []struct {
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desc string
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lines int
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height int
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events func()
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want int
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}{
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{
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desc: "all content fits, draws from the first line",
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lines: 2,
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height: 2,
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want: 0,
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},
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{
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desc: "content doesn't fit, draws up to the last line",
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lines: 4,
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height: 2,
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want: 2,
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},
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{
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desc: "draws up to the last line when height decreases",
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lines: 4,
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height: 1,
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want: 3,
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},
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{
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desc: "draws up to the last line when height increases",
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lines: 4,
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height: 2,
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want: 2,
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},
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{
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desc: "user scrolling breaks away from the last line",
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lines: 4,
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height: 2,
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events: func() {
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st.upOneLine()
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},
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want: 1,
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},
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{
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desc: "keeps scrolled to position when new content arrives",
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lines: 5,
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height: 2,
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want: 1,
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},
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{
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desc: "scrolling down to the last line displays the latest line",
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lines: 5,
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height: 2,
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events: func() {
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st.downOneLine()
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st.downOneLine()
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st.downOneLine()
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},
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want: 3,
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},
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{
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desc: "rolling of new content resumes",
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lines: 6,
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height: 2,
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want: 4,
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},
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{
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desc: "scroll up breaks away from the last line again",
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lines: 6,
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height: 2,
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events: func() {
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st.upOneLine()
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},
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want: 3,
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},
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{
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desc: "keeps scrolled to position when new content arrives again",
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lines: 7,
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height: 2,
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want: 3,
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},
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{
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desc: "resize so that the last line becomes visible",
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lines: 7,
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height: 7,
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want: 0,
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},
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{
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desc: "rolls content after the resize",
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lines: 8,
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height: 7,
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want: 1,
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},
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}
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for _, tc := range tests {
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t.Run(tc.desc, func(t *testing.T) {
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if tc.events != nil {
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tc.events()
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}
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got := st.firstLine(tc.lines, tc.height)
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if got != tc.want {
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t.Errorf("firstLine => got %d, want %d", got, tc.want)
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}
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})
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}
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}
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func TestNormalizeScroll(t *testing.T) {
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tests := []struct {
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desc string
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first int
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lines int
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height int
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want int
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}{
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{
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desc: "first line is negative",
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first: -1,
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lines: 3,
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height: 1,
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want: 0,
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},
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{
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desc: "no lines to be printed",
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first: 0,
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lines: 0,
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height: 1,
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want: 0,
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},
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{
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desc: "zero height",
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first: 0,
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lines: 1,
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height: 0,
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want: 0,
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},
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{
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desc: "first line is greater than the number of lines",
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first: 4,
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lines: 3,
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height: 2,
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want: 1,
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},
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{
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desc: "first line reset to start if the full content fits",
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first: 1,
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lines: 3,
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height: 3,
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want: 0,
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},
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{
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desc: "valid first line",
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first: 2,
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lines: 4,
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height: 2,
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want: 2,
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},
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}
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for _, tc := range tests {
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t.Run(tc.desc, func(t *testing.T) {
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got := normalizeScroll(tc.first, tc.lines, tc.height)
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if got != tc.want {
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t.Errorf("normalizeScroll => got %d, want %d", got, tc.want)
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}
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})
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}
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}
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