From 804e477d50b7abaf486ba4e94ce4716b07285dc8 Mon Sep 17 00:00:00 2001
From: Drath <drath@drath.cc>
Date: Sun, 14 Jun 2026 11:55:14 +0200
Subject: [PATCH] optimize sending custom chars, one write operation now

---
 include/lcd.h |  3 ++-
 src/lcd.c     | 12 +++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/lcd.h b/include/lcd.h
index b3dde6c..806a456 100644
--- a/include/lcd.h
+++ b/include/lcd.h
@@ -10,7 +10,8 @@
 struct lcd_t {
 	int fd;
 	uint32_t baud;
-	char writebuf[LCD_LINES * LCD_COLS + 8];
+	char ccharbuf[8][11];                    // 8 custom chars, each 11 bytes (3 byte command + 8 byte glyph)
+	char writebuf[LCD_LINES * LCD_COLS + 8]; // number of chars on the lcd + 2*4 byte set cursor commands
 	char port[96];
 };
 
diff --git a/src/lcd.c b/src/lcd.c
index 0accaec..d132242 100644
--- a/src/lcd.c
+++ b/src/lcd.c
@@ -59,11 +59,10 @@ void lcd_set_cursor(struct lcd_t *lcd, const uint8_t row, const uint8_t col) {
 	lcd_write(lcd, cmdbuf, sizeof(cmdbuf));
 }
 
-/* reconsider so im not writing every time. prepend custom chars to the write buffer? */
 void lcd_set_custom_char(struct lcd_t *lcd, const uint8_t index, const lcd_glyph_t *glyph) {
 	uint8_t cmdbuf[] = {254, 78, index, 0, 0, 0, 0, 0, 0, 0, 0};
 	memcpy(&cmdbuf[3], glyph, sizeof(lcd_glyph_t));
-	lcd_write(lcd, cmdbuf, sizeof(cmdbuf));
+	memcpy(lcd->ccharbuf[index], cmdbuf, sizeof(cmdbuf));
 }
 
 /* writes string to write buffer at calculated pos, we trust it to be null terminated */
@@ -104,7 +103,8 @@ inline void lcd_flush_buf(struct lcd_t *lcd) {
 	memcpy(&lcd->writebuf[0], set_disp, 4);
 	memcpy(&lcd->writebuf[2 * LCD_COLS + 4], set_disp, 4);
 	lcd->writebuf[2 * LCD_COLS + 7] = 3; // overwrite set cursor c1 l1 to c1 l3
-	lcd_write(lcd, (const uint8_t *)lcd->writebuf, sizeof(lcd->writebuf));
+	// hacky, relies on charbuf being before writebuf in the lcd struct. we start at the charbuf pointer and write both at the same time
+	lcd_write(lcd, (const uint8_t *)lcd->ccharbuf, sizeof(lcd->ccharbuf) + sizeof(lcd->writebuf));
 }
 
 // i have a whole flushbuf func to avoid too many writes, but im writing on every bar, need to rethink this.
@@ -131,6 +131,12 @@ int lcd_init(struct lcd_t *lcd) {
 	tcflush(lcd->fd, TCIFLUSH);
 	tcsetattr(lcd->fd, TCSANOW, &term);
 
+	// zero out custom chars
+	for (uint8_t i = 0; i < 8; i++) {
+		const uint8_t charbuf[] = {254, 78, i, 0, 0, 0, 0, 0, 0, 0, 0};
+		memcpy(lcd->ccharbuf[i], charbuf, sizeof(charbuf));
+	}
+
 	lcd_clear_buf(lcd);
 	const uint8_t cmdbuf[] = {254, 75, 254, 84};
 	lcd_write(lcd, cmdbuf, sizeof(cmdbuf));