Lesson 31 · Highlighting the match

Highlighting the match

A found match should stand out on screen. Today you remember the last match and mark it in the rendered frame, tying search into the viewport.

The goal

Remember the current match span and bracket it in the rendered frame; clear it when the text is edited.

Start here - the target

TO DO

Scenario: Marking the current match in the frame

Givenan editor over the single line "foo bar" rendered at width 20

WhenFindNext("bar") succeeds and the frame is rendered

Thenthe rendered line is "foo [bar]" (the match wrapped in square brackets)

Andafter any edit (such as InsertChar) the highlight is cleared, so the line renders as plain text again

Background

A match you cannot see is only half a search. When a find succeeds, the editor remembers where the match is - its row, column, and length - and the renderer draws attention to it by wrapping it in brackets, the same plain-text highlighting trick the fuzzy-finder used to stay terminal-independent. In a real terminal those brackets become reverse-video, but as a string they are exact and testable: "foo bar" with bar found renders as "foo [bar]".

The important half is invalidation. A remembered match is only valid until the text changes - insert a character and the offsets shift, so a stale highlight would bracket the wrong span. So every editing operation clears the match, and the highlight simply disappears until the next find. This is the first feature to couple search and rendering, and handling the “the text moved out from under it” case now is what makes the next lesson - replacing the very match you just found - safe.

Make it work

// a successful find records the match: matchRow, matchCol, matchLen.
// in Render, on the match row, splice "[" before matchCol and "]"
// after matchCol+matchLen.
// every editing op clears the match (matchLen = 0) so a stale
// highlight never lingers over changed text.

CheckpointDONE

The editor highlights the current search match. Commit and stop here.