From f3c2c0ffa9abaaa737ef41a0a4720518ce75f775 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 30 Mar 2023 19:11:00 -0400
Subject: [PATCH] Synchronise fetch and draw sprite buffer usage.

---
 Components/9918/Implementation/9918.cpp       | 9 +++++++--
 Components/9918/Implementation/LineBuffer.hpp | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index dca9ac02c..54002dd45 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -131,8 +131,11 @@ void Base<personality>::posit_sprite(int sprite_number, int sprite_position, uin
 	// Evaluation of visibility of sprite 0 is always the first step in
 	// populating a sprite buffer; so use it to uncork a new one.
 	if(!sprite_number) {
+		fetch_line_buffer_->fetched_sprites = true;
+
 		advance(fetch_sprite_buffer_);
 		fetch_sprite_buffer_->reset_sprite_collection();
+		fetch_sprite_buffer_->sprite_terminator = mode_timing_.sprite_terminator(fetch_line_buffer_->screen_mode);
 	}
 
 	if(!(status_ & StatusSpriteOverflow)) {
@@ -359,7 +362,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 				this->fetch_line_buffer_->next_border_column = Timing<personality>::CyclesPerLine;
 				this->fetch_line_buffer_->pixel_count = 256;
 				this->fetch_line_buffer_->screen_mode = this->screen_mode_;
-//				mode_timing_.sprite_terminator(buffer.screen_mode);
+				this->fetch_line_buffer_->fetched_sprites = false;
 				this->mode_timing_.maximum_visible_sprites = 4;
 				switch(this->screen_mode_) {
 					case ScreenMode::Text:
@@ -598,8 +601,10 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 				// -------------
 				this->output_pointer_.column = end_column;
 				if(end_column == Timing<personality>::CyclesPerLine) {
+					if(this->draw_line_buffer_->fetched_sprites) {
+						this->advance(this->draw_sprite_buffer_);
+					}
 					this->advance(this->draw_line_buffer_);
-					this->advance(this->draw_sprite_buffer_);
 				}
 			}
 
diff --git a/Components/9918/Implementation/LineBuffer.hpp b/Components/9918/Implementation/LineBuffer.hpp
index 0af99d6d5..6d9c9b71b 100644
--- a/Components/9918/Implementation/LineBuffer.hpp
+++ b/Components/9918/Implementation/LineBuffer.hpp
@@ -22,6 +22,7 @@ struct LineBuffer {
 	FetchMode fetch_mode = FetchMode::Text;
 	ScreenMode screen_mode = ScreenMode::Text;
 	VerticalState vertical_state = VerticalState::Blank;
+	bool fetched_sprites = false;
 
 	// Holds the horizontal scroll position to apply to this line;
 	// of those VDPs currently implemented, affects the Master System only.