From 70c772aedfabb36c5f3052cc4454ba591be2d308 Mon Sep 17 00:00:00 2001
From: WormHeamer
Date: Tue, 4 Nov 2025 22:03:44 -0500
Subject: clarify scrolling behavior in comment

---
 main.c | 48 ++++++++++++++++++++++++++++--------------------
 1 file changed, 28 insertions(+), 20 deletions(-)

(limited to 'main.c')

diff --git a/main.c b/main.c
index bf79c26..c25a174 100644
--- a/main.c
+++ b/main.c
@@ -435,10 +435,12 @@ void vui_blit(void) {
 	static unsigned cur_x = 0;
 	static unsigned cur_y = 0;
 
+	/*
 		vui_outs(CSI "H" CSI "0m");
 		attr_last = ATTR_DEFAULT;
 		cur_x = 0;
 		cur_y = 0;
+	*/
 
 	scrolled_x = vui_win.scroll_x;
 	scrolled_y = vui_win.scroll_y;
@@ -473,41 +475,42 @@ void vui_blit(void) {
 	vui_changes = 0;
 	vui_max_change = 0;
 
-	/* TODO:
-	 *
-	 * Scroll without repainting whole screen:
-	 *
-	 * - \x1b[#L to insert blank lines
-	 * - \x1b[#@ to insert blank chars
-	 * - \x1b[#M to delete lines
-	 * - \x1b[#P to delete chars
-	 *
-	 */
-
 	if (vui_win.scroll_x || vui_win.scroll_y) {
 		if (abs(vui_win.scroll_x) >= COLS || abs(vui_win.scroll_y) > LINES) {
 			vui_outs(CSI "2J");
 			goto scrolled;
 		}
 
+		/* spaces inserted by scrolling will have the last-used attribute */
+		/* which we don't really want */
+		attr_chg(&attr_last, ATTR_DEFAULT);
+
 		if (vui_win.scroll_x < 0) {
+			/* delete chars at start of line */
 			for (unsigned y = 0; y < LINES; y++) {
 				curs_move(&cur_x, &cur_y, 0, y);
 				vui_outf(CSI "%dP", -vui_win.scroll_x);
 			}
 		} else if (vui_win.scroll_x > 0) {
+			/* insert spaces at start of line */
 			for (unsigned y = 0; y < LINES; y++) {
 				curs_move(&cur_x, &cur_y, 0, y);
 				vui_outf(CSI "%d@", vui_win.scroll_x);
 			}
 		}
 
+		/* xterm has \x1b[S and \x1b[T to scroll directly */
+		/* but these don't work in linux vtty */
 		if (vui_win.scroll_y < 0) {
-			if (vui_win.scroll_y == -1) vui_outs(CSI "S");
-			else vui_outf(CSI "%dS", -vui_win.scroll_y);
+			/* delete lines at top */
+			curs_move(&cur_x, &cur_y, 0, 0);
+			if (vui_win.scroll_y == -1) vui_outs(CSI "M");
+			else vui_outf(CSI "%dM", -vui_win.scroll_y);
 		} else if (vui_win.scroll_y > 0) {
-			if (vui_win.scroll_y == 1) vui_outs(CSI "T");
-			else vui_outf(CSI "%dT", vui_win.scroll_y);
+			/* insert blank lines at top */
+			curs_move(&cur_x, &cur_y, 0, 0);
+			if (vui_win.scroll_y == 1) vui_outs(CSI "L");
+			else vui_outf(CSI "%dL", vui_win.scroll_y);
 		}
 
 scrolled:
@@ -641,7 +644,7 @@ int dx = 0, dy = 0;
 int camx = 0, camy = 0;
 int C = '*';
 unsigned frame = 0;
-int half_y = 1;
+int half_y = 0;
 
 void draw(void *ctx) {
 	(void)ctx;
@@ -724,8 +727,10 @@ int main(int argc, const char **argv) {
 			for (unsigned i = 0; i < isqrt(COLS * LINES) / 10; i++) {
 				int tx = random() % COLS;
 				int ty = random() % LINES;
-				VuiAttr a = ((random()&15) << 4) | (random()&15);
-				vui_chra(tx, ty, ' ' + (random() % 0x5f), a);
+				// VuiAttr a = ((random()&15) << 4) | (random()&15);
+				char ch = ' ' + (random() % 0x5f);
+				VuiAttr a = random() & ((1 << 13) - 1);
+				vui_chra(tx, ty, ch, a);
 			}
 		}
 
@@ -735,9 +740,12 @@ int main(int argc, const char **argv) {
 			for (unsigned x = 0; x < COLS; x++) {
 				int tx = x + camx, ty = y + camy;
 				char ch = " ',."[(tx^ty)&3];
-				int abp = (((tx>>4)^(ty>>4)) % 3 == 0);
+				/* int abp = (((tx>>4)^(ty>>4)) % 3 == 0);
 				VuiAttr aa = abp ? BG_CYAN : BG_WHITE;
-				VuiAttr ab = abp ? BG_BLUE : BG_RED;
+				VuiAttr ab = abp ? BG_BLUE : BG_RED; */
+				unsigned abp = (tx >> 4) ^ (ty >> 4);
+				VuiAttr aa = (abp & 15) << 4;
+				VuiAttr ab = ((abp+1) & 15) << 4;
 				VuiAttr a = (((tx>>2)^(ty>>2)) % 3 == 0) ? aa : ab;
 				vui_chra(x, y, ch, a);
 			}
-- 
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