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Renderers: linear per-row measuring in ImGui; one tab width; Qt drawing fixes

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ImGui measured every span, highlight and the cursor from column 0 of the
line (and rescanned the line for each column conversion), which is
quadratic in line length on minified files. Columns now come from one
table per line and pixel offsets from the nearest position already
measured. Output is pixel-identical to before (compared under Xvfb, with
syntax colouring, tabs, UTF-8 and search highlights).

kte::kTabWidth replaces the literal 8s, and Qt's 4: Qt expanded tabs to
4 columns while the command layer scrolled by 8, misplacing the cursor
and horizontal scroll on lines with tabs. MeasureChar and
DisplayColumns (TermWidth.h) are the command layer's column model, now
shared, and Qt draws by it instead of one column per byte, which
shifted everything after a multi-byte character.

Qt also:
- drew operators in the dark-mode background colour, so they vanished;
- computed the editor's column count three ways (different glyph,
  padding and status-row accounting) from painting, and positioned text
  with a rounded cell width, so the cursor drifted off the glyphs on long
  lines. One TextLayout now serves painting, resizing, font changes and
  wheel scrolling, with a fractional cell width; runs are drawn only
  where visible;
- drew each non-ASCII character at its cell, since a fallback-font glyph
  wider than a cell pushed the rest of the run out of place.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015rcVQiiWyTzoNrsvLSaAfB
This commit is contained in:
Claude
2026-09-24 12:19:59 -07:00
committed by Kyle Isom
parent 29d0ee8244
commit 323e2377fe
6 changed files with 227 additions and 223 deletions
Download Patch File Download Diff File Expand all files Collapse all files
ImGuiRenderer.cc
+42 -46
View File
@@ -10,6 +10,7 @@
#include "ImGuiRenderer.h"
#include "SearchHighlight.h"
#include "TermWidth.h"
#include "Highlight.h"
#include "GUITheme.h"
#include "Buffer.h"
@@ -220,7 +221,7 @@ ImGuiRenderer::Draw(Editor &ed)
// Expand tabs for the clicked line
std::string line_clicked = buf->GetLineString(by);
const std::size_t tabw = 8;
const std::size_t tabw = kte::kTabWidth;
std::string click_expanded;
click_expanded.reserve(line_clicked.size() + 16);
std::size_t click_rx = 0;
@@ -315,48 +316,52 @@ ImGuiRenderer::Draw(Editor &ed)
ImVec2 line_pos = ImGui::GetCursorScreenPos();
std::string line = buf->GetLineString(i);
// Expand tabs to spaces with width=8
const std::size_t tabw = 8;
// Expand tabs to spaces with width=8, recording each source
// byte's rendered column (rx_of[line.size()] is the line's width).
const std::size_t tabw = kte::kTabWidth;
std::string expanded;
expanded.reserve(line.size() + 16);
std::size_t rx_abs_draw = 0;
std::vector<std::size_t> rx_of(line.size() + 1);
for (std::size_t src = 0; src < line.size(); ++src) {
char c = line[src];
if (c == '\t') {
std::size_t adv = (tabw - (rx_abs_draw % tabw));
expanded.append(adv, ' ');
rx_abs_draw += adv;
} else {
expanded.push_back(c);
rx_abs_draw += 1;
}
rx_of[src] = expanded.size();
if (line[src] == '\t')
expanded.append(tabw - (expanded.size() % tabw), ' ');
else
expanded.push_back(line[src]);
}
rx_of[line.size()] = expanded.size();
auto src_to_rx = [&](std::size_t src) -> std::size_t {
return rx_of[std::min(src, line.size())];
};
// Helper: convert a rendered column position to an absolute
// pixel x offset from the start of the line. ImGui's scroll
// handles viewport clipping so we measure from column 0.
// Rendered column -> pixel offset from the start of the line.
// Measuring from column 0 for every span was quadratic in line
// length; measure on from the nearest earlier position already
// measured (only character boundaries are kept, so a multi-byte
// character is never measured in pieces).
std::vector<std::pair<std::size_t, float> > px_marks{{0, 0.0f}}; // unrounded
auto rx_to_px = [&](std::size_t rx_col) -> float {
std::size_t end = std::min(expanded.size(), rx_col);
if (end == 0)
return 0.0f;
return ImGui::CalcTextSize(expanded.c_str(),
expanded.c_str() + end).x;
const std::size_t end = std::min(expanded.size(), rx_col);
auto it = std::upper_bound(px_marks.begin(), px_marks.end(), end,
[](std::size_t v, const std::pair<std::size_t, float> &m) {
return v < m.first;
});
--it; // px_marks[0] is column 0
float px = it->second;
if (it->first != end) {
px += ImGui::GetFont()->CalcTextSizeA(ImGui::GetFontSize(), FLT_MAX, 0.0f,
expanded.c_str() + it->first,
expanded.c_str() + end).x;
if (end == expanded.size() || (static_cast<unsigned char>(expanded[end]) & 0xC0) != 0x80)
px_marks.insert(it + 1, {end, px});
}
// Rounded up as ImGui::CalcTextSize does (sums of rounded
// pieces would drift).
return end == 0 ? 0.0f : static_cast<float>(static_cast<int>(px + 0.99999f));
};
// Search highlight ranges for this line in source indices
search_hl.Ranges(line, hl_src_ranges);
auto src_to_rx = [&](std::size_t upto_src_exclusive) -> std::size_t {
std::size_t rx = 0;
std::size_t s = 0;
while (s < upto_src_exclusive && s < line.size()) {
if (line[s] == '\t')
rx += (tabw - (rx % tabw));
else
rx += 1;
++s;
}
return rx;
};
// Draw background highlights (under text)
if (search_mode && !hl_src_ranges.empty()) {
// Current match emphasis
@@ -461,18 +466,9 @@ ImGuiRenderer::Draw(Editor &ed)
return a.s < b.s;
});
// Helper to convert a src column to expanded rx position
auto src_to_rx_full = [&](std::size_t sidx) -> std::size_t {
std::size_t rx = 0;
for (std::size_t k = 0; k < sidx && k < line.size(); ++k) {
rx += (line[k] == '\t') ? (tabw - (rx % tabw)) : 1;
}
return rx;
};
for (const auto &sp: spans) {
std::size_t rx_s = src_to_rx_full(sp.s);
std::size_t rx_e = src_to_rx_full(sp.e);
std::size_t rx_s = src_to_rx(sp.s);
std::size_t rx_e = src_to_rx(sp.e);
std::size_t draw_start = rx_s;
if (draw_start >= expanded.size())
continue;
@@ -515,7 +511,7 @@ ImGuiRenderer::Draw(Editor &ed)
// measured per frame; if the user scrolls or edits, the cache is
// refreshed accordingly.
if (!expanded.empty()) {
float line_w = ImGui::CalcTextSize(expanded.c_str()).x;
const float line_w = rx_to_px(expanded.size());
if (line_w > max_width_px_)
max_width_px_ = line_w;
}
@@ -575,7 +571,7 @@ ImGuiRenderer::Draw(Editor &ed)
float cursor_px_abs = 0.0f;
if (cy < nlines) {
std::string cur_line = buf->GetLineString(cy);
const std::size_t tabw = 8;
const std::size_t tabw = kte::kTabWidth;
// Expand tabs for cursor line to measure pixel position
std::string cur_expanded;
cur_expanded.reserve(cur_line.size() + 16);