# HG changeset patch
# User Michael Pavone <pavone@retrodev.com>
# Date 1724821804 25200
# Node ID e51b1fc0e37f357c91eaf84dd01e676ed97b6462
# Parent  0a22c1901492acf34082b52e891bb4c5be947cee
Fix rendering of sprites that are partially off the top of the screen in Mode 4

diff -r 0a22c1901492 -r e51b1fc0e37f vdp.c
--- a/vdp.c	Tue Aug 27 21:27:21 2024 -0700
+++ b/vdp.c	Tue Aug 27 22:10:04 2024 -0700
@@ -794,13 +794,16 @@
 static void scan_sprite_table_mode4(vdp_context * context)
 {
 	if (context->sprite_index < MAX_SPRITES_FRAME_H32) {
-		uint32_t line = context->vcounter;
+		int16_t line = context->vcounter;
 		line &= 0xFF;
+		if (line > context->inactive_start) {
+			line -= 0x100;
+		}
 
 		uint32_t sat_address = mode4_address_map[(context->regs[REG_SAT] << 7 & 0x3F00) + context->sprite_index];
-		uint32_t y = context->vdpmem[sat_address+1];
+		int16_t y = context->vdpmem[sat_address+1];
 		uint32_t size = (context->regs[REG_MODE_2] & BIT_SPRITE_SZ) ? 16 : 8;
-		uint32_t ysize = size;
+		int16_t ysize = size;
 		uint8_t zoom = context->type != VDP_GENESIS && (context->regs[REG_MODE_2] & BIT_SPRITE_ZM);
 		if (zoom) {
 			ysize *= 2;
@@ -810,6 +813,9 @@
 			context->sprite_index = MAX_SPRITES_FRAME_H32;
 			return;
 		} else {
+			if (y > context->inactive_start) {
+				y -= 0x100;
+			}
 			if (y <= line && line < (y + ysize)) {
 				if (!context->slot_counter) {
 					context->sprite_index = MAX_SPRITES_FRAME_H32;
@@ -829,6 +835,9 @@
 				context->sprite_index = MAX_SPRITES_FRAME_H32;
 				return;
 			} else {
+				if (y > context->inactive_start) {
+					y -= 0x100;
+				}
 				if (y <= line && line < (y + ysize)) {
 					if (!context->slot_counter) {
 						context->sprite_index = MAX_SPRITES_FRAME_H32;
@@ -919,7 +928,11 @@
 		if (context->regs[REG_MODE_2] & BIT_SPRITE_SZ) {
 			tile_address &= ~32;
 		}
-		uint16_t y_diff = context->vcounter - context->sprite_info_list[context->cur_slot].y;
+		int16_t line = context->vcounter & 0xFF;
+		if (context->vcounter > context->inactive_start) {
+			line -= 0x100;
+		}
+		uint16_t y_diff = line - context->sprite_info_list[context->cur_slot].y;
 		if (zoom) {
 			y_diff >>= 1;
 		}