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Merge pull request 'perf(input-field): O(n) cursor hit test via Font::NearestCursorByte (#56)' (#90) from claude/issue-56 into master

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catbot 2026-06-16 18:55:34 +02:00
commit 79db987f83
6 changed files with 280 additions and 16 deletions
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24
implementations/Crafter.Graphics-Font.cpp
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@ -72,6 +72,30 @@ std::uint32_t Font::GetLineWidth(const std::string_view text, float size) {
return lineWidth;
}
std::size_t Font::NearestCursorByte(std::string_view text, float size, float target) {
if (target <= 0.0f) return 0;
float scale = stbtt_ScaleForPixelHeight(&font, size);
std::size_t best = 0; // byte offset 0 → caret before the first glyph
float bestDist = target; // |target - 0|, and target > 0 here
float cumWidth = 0.0f;
std::size_t i = 0;
while (i < text.size()) {
std::uint32_t cp = DecodeUtf8(text, i); // i advances to the next boundary
if (cp == 0) break;
int advance, lsb;
stbtt_GetCodepointHMetrics(&font, static_cast<int>(cp), &advance, &lsb);
cumWidth += (int)(advance * scale); // match GetLineWidth's per-glyph rounding
float d = std::abs(target - cumWidth);
if (d < bestDist) {
bestDist = d;
best = i; // byte offset just past this codepoint
} else {
break; // monotonic advance ⇒ already past the closest boundary
}
}
return best;
}
float Font::LineHeight(float size) {
float scale = stbtt_ScaleForPixelHeight(&font, size);
return (ascent - descent + lineGap) * scale;

21
implementations/Crafter.Graphics-InputField.cpp
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@ -117,23 +117,12 @@ std::size_t Crafter::InputField_HitTestCursor(const InputField& f,
Font& font, float fontSize,
const InputFieldColors& colors)
{
// Single O(n) cumulative-advance pass over the value, keyed at codepoint
// byte boundaries — matching cursorPos, which is a byte offset. The old
// loop re-walked the prefix for every boundary (O(n^2) glyph metric
// lookups) and could even land mid-codepoint on multibyte input.
float target = clickX - (rect.x + colors.paddingX);
if (target <= 0.0f) return 0;
std::size_t best = 0;
float bestDist = std::abs(target);
for (std::size_t i = 1; i <= f.value.size(); ++i) {
std::string_view sub(f.value.data(), i);
float w = static_cast<float>(font.GetLineWidth(sub, fontSize));
float d = std::abs(target - w);
if (d < bestDist) {
bestDist = d;
best = i;
} else {
break;
}
}
return best;
return font.NearestCursorByte(f.value, fontSize, target);
}
void Crafter::DrawInputField(UIBuffer& buf, const InputField& f, Rect rect,