From 42ebe064748b4f7094b1dece741e4f7fa95e7417 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 8 Oct 2019 23:06:50 -0400
Subject: [PATCH] Makes an attempt at tracking video sequence points.

---
 Machines/AtariST/AtariST.cpp | 12 +++++++++++-
 Machines/AtariST/Video.cpp   |  1 +
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/Machines/AtariST/AtariST.cpp b/Machines/AtariST/AtariST.cpp
index 68303d23c..cfb29d714 100644
--- a/Machines/AtariST/AtariST.cpp
+++ b/Machines/AtariST/AtariST.cpp
@@ -272,9 +272,18 @@ class ConcreteMachine:
 
 	private:
 		forceinline void advance_time(HalfCycles length) {
-			video_ += length;
 			cycles_since_audio_update_ += length;
 			mfp_ += length;
+
+			while(length >= cycles_until_video_event_) {
+				length -= cycles_until_video_event_;
+				video_ += cycles_until_video_event_;
+				cycles_until_video_event_ = video_->get_next_sequence_point();
+
+				// TODO: push v/hsync/display_enable elsewhere.
+			}
+			cycles_until_video_event_ -= length;
+			video_ += length;
 		}
 
 		void update_audio() {
@@ -284,6 +293,7 @@ class ConcreteMachine:
 		CPU::MC68000::Processor<ConcreteMachine, true> mc68000_;
 		JustInTimeActor<Video, HalfCycles> video_;
 		JustInTimeActor<Motorola::MFP68901::MFP68901, HalfCycles> mfp_;
+		HalfCycles cycles_until_video_event_;
 
 		Concurrency::DeferringAsyncTaskQueue audio_queue_;
 		GI::AY38910::AY38910 ay_;
diff --git a/Machines/AtariST/Video.cpp b/Machines/AtariST/Video.cpp
index 9c5e2a2d4..976e8e5c6 100644
--- a/Machines/AtariST/Video.cpp
+++ b/Machines/AtariST/Video.cpp
@@ -167,6 +167,7 @@ HalfCycles Video::get_next_sequence_point() {
 		} else if(y >= mode_params.final_video_line ) {
 			vertical_lines = mode_params.first_video_line + mode_params.lines_per_frame - y;
 		}
+		if(horizontal_cycles < 0) ++vertical_lines;
 		cycles_until_display_enable = HalfCycles(horizontal_cycles + vertical_lines * mode_params.line_length);
 	}