A selection deep in a long line costs a render what one at its start does: 5 MB in, /screen goes from 14.7 s to 5 ms

Every render measured a selection's and the cursor's columns from the
start of their line (lineDisplayOffset walked the whole prefix twice),
so a selection near the end of a 5 MB line stalled each frame, 3 s at
1 MB in and 14.7 s at 5 MB. The cost grew with the offset, with Wrap on
or off. Three changes make it independent of where the selection is:
- display width adds (a tab is tab_width wherever it stands), so the
  offset between two columns is the width of the text between them,
  never the prefix;
- the selection's rows are clamped to what is shown: a row wholly
  before the selection is skipped, a start before the row's first
  column starts there, and an end past its last column ends there;
- a head or cursor whose column lies past its visible row (the last
  visible row of a line owns every column after its start) is not
  measured, since it is not drawn.
Measured on a Debug build, 5 MB line: offset 10, 1 MB and 5 MB now take
11, 6 and 5 ms per /screen. A new perf gate case, deep-sel, renders with
the selection 2 MB into a line: 83 us on Debug. The baselines were
re-recorded for the new harness.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/test/perf-baseline-tty-ReleaseFast.json b/test/perf-baseline-tty-ReleaseFast.json
index 66421ba3..87a31754 100644
--- a/test/perf-baseline-tty-ReleaseFast.json
+++ b/test/perf-baseline-tty-ReleaseFast.json
@@ -1 +1 @@
-{"harness":"f420fe5db60d6e97","build":{"compiler":"0.16.0","target":"x86_64-linux.5.10...6.19-gnu.2.38","cpu":"x86_64","driver_optimize":"ReleaseFast","core_optimize":"ReleaseFast","c_optimize":"ReleaseFast","terminal_optimize":"ReleaseFast","platform":"tty","grammars":"full","mupdf":true,"jpx":true,"tracy":false,"quic":false,"theme_animation":true,"terminal_simd":true,"prebuilt_shaders":false},"cols":120,"rows":40,"reps":10,"only":"medium","fixtures":[{"name":"small","lines":1000,"cols":60,"bytes":62694},{"name":"medium","lines":50000,"cols":60,"bytes":3201944},{"name":"large","lines":300000,"cols":60,"bytes":19464444},{"name":"longline","lines":400,"cols":8000,"bytes":3200400},{"name":"esp32p4","lines":12,"cols":240,"bytes":2892}],"cells":[{"op":"open","fixture":"medium","min_us":1751,"med_us":2134,"p90_us":2183,"max_us":2415},{"op":"render","fixture":"medium","min_us":76,"med_us":77,"p90_us":91,"max_us":92},{"op":"key-down","fixture":"medium","min_us":77,"med_us":78,"p90_us":82,"max_us":83},{"op":"key-right","fixture":"medium","min_us":79,"med_us":85,"p90_us":100,"max_us":102},{"op":"page-down","fixture":"medium","min_us":78,"med_us":82,"p90_us":86,"max_us":95},{"op":"wheel","fixture":"medium","min_us":76,"med_us":79,"p90_us":83,"max_us":87},{"op":"edit-char","fixture":"medium","min_us":1063,"med_us":1290,"p90_us":1527,"max_us":1564},{"op":"body-2m","fixture":"medium","min_us":4950,"med_us":9414,"p90_us":10945,"max_us":13152},{"op":"body-appends","fixture":"medium","min_us":117839,"med_us":189253,"p90_us":232943,"max_us":247720}]}
+{"harness":"e63a8b27a0bcb261","build":{"compiler":"0.16.0","target":"x86_64-linux.5.10...6.19-gnu.2.38","cpu":"x86_64","driver_optimize":"ReleaseFast","core_optimize":"ReleaseFast","c_optimize":"ReleaseFast","terminal_optimize":"ReleaseFast","platform":"tty","grammars":"full","mupdf":true,"jpx":true,"tracy":false,"quic":false,"theme_animation":true,"terminal_simd":true,"prebuilt_shaders":false},"cols":120,"rows":40,"reps":10,"only":"medium","fixtures":[{"name":"small","lines":1000,"cols":60,"bytes":62694},{"name":"medium","lines":50000,"cols":60,"bytes":3201944},{"name":"large","lines":300000,"cols":60,"bytes":19464444},{"name":"longline","lines":400,"cols":8000,"bytes":3200400},{"name":"esp32p4","lines":12,"cols":240,"bytes":2892}],"cells":[{"op":"open","fixture":"medium","min_us":2042,"med_us":2280,"p90_us":2451,"max_us":2478},{"op":"render","fixture":"medium","min_us":82,"med_us":84,"p90_us":87,"max_us":104},{"op":"key-down","fixture":"medium","min_us":83,"med_us":86,"p90_us":90,"max_us":93},{"op":"key-right","fixture":"medium","min_us":84,"med_us":87,"p90_us":91,"max_us":104},{"op":"page-down","fixture":"medium","min_us":84,"med_us":87,"p90_us":93,"max_us":96},{"op":"wheel","fixture":"medium","min_us":81,"med_us":85,"p90_us":89,"max_us":89},{"op":"edit-char","fixture":"medium","min_us":1309,"med_us":1613,"p90_us":1840,"max_us":2128},{"op":"body-2m","fixture":"medium","min_us":5386,"med_us":11064,"p90_us":11706,"max_us":12374},{"op":"body-appends","fixture":"medium","min_us":144772,"med_us":232307,"p90_us":273586,"max_us":281169},{"op":"deep-sel","fixture":"medium","min_us":79,"med_us":83,"p90_us":87,"max_us":130}]}