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perf(ui): O(n) FullscreenMsgView wrap via getCodepointWidth virtual

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The wrap loop used to memcpy a growing substring and call getTextWidth
on it for every appended codepoint — O(n²) UTF-8 decoding with Lemon
font, ~5-20 ms on a full e-ink redraw of a long message.

Add DisplayDriver::getCodepointWidth(cp) (default: build a UTF-8 buffer
and forward to getTextWidth) plus DisplayDriver::decodeCodepoint() as
the shared UTF-8 walker. Override getCodepointWidth in GxEPDDisplay
(direct lemonXAdvance for Lemon size 1) and SH1106Display (lemonXAdvance
for Lemon, fixed 6*sz for built-in font). FullscreenMsgView now walks
codepoints once and sums widths incrementally.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Jakub
2026-05-24 20:22:16 +02:00
parent 87bdc5cb9f
commit 74764aed2b
4 changed files with 68 additions and 19 deletions
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36
examples/companion_radio/ui-new/FullscreenMsgView.h
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@@ -16,33 +16,33 @@ struct FullscreenMsgView {
void begin() { scroll = 0; active = true; }
// Pixel-accurate word-wrap: breaks at last space that fits within max_px,
// hard-breaks long words. Works for both fixed- and variable-width fonts.
// hard-breaks long words. Walks the string codepoint-by-codepoint, summing
// per-codepoint widths via DisplayDriver::getCodepointWidth — O(n) instead
// of O(n²) substring re-measurement. Works for both fixed- and
// variable-width fonts.
static int wrapLines(DisplayDriver& display, const char* text, int max_px,
char out[][FS_CHARS_MAX], int max_lines) {
int count = 0;
const char* seg = text;
const uint8_t* seg = (const uint8_t*)text;
while (*seg && count < max_lines) {
const char* p = seg;
const char* last_sp = nullptr;
const char* last_fit = seg;
const uint8_t* p = seg;
const uint8_t* last_sp = nullptr; // pointer to space byte (cut here, drop the space)
const uint8_t* last_fit = seg; // farthest point that still fits
int width = 0;
while (*p && (p - seg) < FS_CHARS_MAX - 1) {
uint8_t b0 = (uint8_t)*p;
int cb = (b0 < 0x80) ? 1 : (b0 < 0xE0) ? 2 : (b0 < 0xF0) ? 3 : 4;
if ((p - seg) + cb >= FS_CHARS_MAX) break;
char buf[FS_CHARS_MAX];
int n = (int)(p - seg) + cb;
memcpy(buf, seg, n); buf[n] = '\0';
if (display.getTextWidth(buf) > max_px && p > seg) break;
if (*p == ' ') last_sp = p;
p += cb;
const uint8_t* cp_start = p;
uint32_t cp = DisplayDriver::decodeCodepoint(p);
if ((p - seg) >= FS_CHARS_MAX) { p = cp_start; break; }
uint16_t cw = display.getCodepointWidth(cp);
if (width + cw > max_px && cp_start > seg) { p = cp_start; break; }
if (cp == ' ') last_sp = cp_start;
width += cw;
last_fit = p;
}
const char* end;
const char* next_seg;
const uint8_t* end;
const uint8_t* next_seg;
if (!*p) {
end = p; next_seg = p;
} else if (last_sp && last_sp > seg) {