From 9c5c2c803c54f2f2ebef4f9cb946117bc414a5fa Mon Sep 17 00:00:00 2001
From: neonloop
Date: Sat, 16 Dec 2023 16:43:16 +0000
Subject: Blends pixels that would be missed during downscale

Avoids entirely missing lines and pixels, improves downscale smoothness
---
 scale.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/scale.c b/scale.c
index 842e4ae..5857589 100644
--- a/scale.c
+++ b/scale.c
@@ -186,7 +186,19 @@ static void scale_blend(unsigned w, unsigned h, size_t pitch, const void *src, v
 			if (!lines)
 				pnext -= (pitch / sizeof(uint16_t));
 
-			if (dy > rat_dst_h - bh[0]) {
+			if (dy <= bh[0] && dy + rat_h > (rat_dst_h + rat_dst_h - bh[0])) {
+				/* Will miss next line, blend in instead */
+				const uint32_t *src32 = (const uint32_t *)src;
+				const uint32_t *pnext32 = (const uint32_t *)pnext;
+				uint32_t *pblend32 = (uint32_t *)pblend;
+				int count = w / 2;
+
+				while(count--) {
+					*pblend32++ = AVERAGE32(*src32, *pnext32);
+					src32++;
+					pnext32++;
+				}
+			} else if (dy > rat_dst_h - bh[0]) {
 				pblend = pnext;
 			} else if (dy <= bh[0]) {
 				/* Drops const, won't get touched later though */
@@ -227,15 +239,17 @@ static void scale_blend(unsigned w, unsigned h, size_t pitch, const void *src, v
 				while (dx < rat_dst_w) {
 					if (a == b) {
 						out = a;
+					} else if (dx <= bw[0] && dx + rat_w > (rat_dst_w + rat_dst_w - bw[0])) {
+						out = AVERAGE16_NOCHK(a, b); // will miss next pixel, blend in instead
 					} else if (dx > rat_dst_w - bw[0]) { // top quintile, bbbb
 						out = b;
 					} else if (dx <= bw[0]) { // last quintile, aaaa
 						out = a;
 					} else {
 						if (dx > rat_dst_w - bw[1]) { // 2nd quintile, abbb
-							a = AVERAGE16_NOCHK(a,b);
+							a = AVERAGE16_NOCHK(a, b);
 						} else if (dx <= bw[1]) { // 4th quintile, aaab
-							b = AVERAGE16_NOCHK(a,b);
+							b = AVERAGE16_NOCHK(a, b);
 						}
 
 						out = AVERAGE16_NOCHK(a, b); // also 3rd quintile, aabb
-- 
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