From b7f069e1bdfb0984b5108c95b15702199ce59e72 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 8 Sep 2024 21:12:45 -0400
Subject: [PATCH] Add a colour burst.

---
 Machines/Acorn/Electron/Video.cpp | 11 ++++++++---
 Machines/Acorn/Electron/Video.hpp |  5 ++++-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/Machines/Acorn/Electron/Video.cpp b/Machines/Acorn/Electron/Video.cpp
index 6c64f598d..ec8f428c7 100644
--- a/Machines/Acorn/Electron/Video.cpp
+++ b/Machines/Acorn/Electron/Video.cpp
@@ -124,7 +124,11 @@ uint8_t VideoOutput::run_for(const Cycles cycles) {
 		if(vsync_int_ || hsync_int_) {
 			stage = OutputStage::Sync;
 		} else if(in_blank()) {
-			stage = OutputStage::Blank;
+			if(h_count_ >= hburst_start && h_count_ < hburst_end) {
+				stage = OutputStage::ColourBurst;
+			} else {
+				stage = OutputStage::Blank;
+			}
 		} else {
 			stage = OutputStage::Pixels;
 			screen_pitch = (mode_40_ ? 320 : 640) / static_cast<int>(mode_bpp_);
@@ -132,8 +136,9 @@ uint8_t VideoOutput::run_for(const Cycles cycles) {
 
 		if(stage != output_ || screen_pitch != screen_pitch_) {
 			switch(output_) {
-				case OutputStage::Sync:		crt_.output_sync(output_length_);					break;
-				case OutputStage::Blank:	crt_.output_blank(output_length_);					break;
+				case OutputStage::Sync:			crt_.output_sync(output_length_);					break;
+				case OutputStage::Blank:		crt_.output_blank(output_length_);					break;
+				case OutputStage::ColourBurst:	crt_.output_default_colour_burst(output_length_);	break;
 				case OutputStage::Pixels:
 					if(current_output_target_) {
 						crt_.output_data(
diff --git a/Machines/Acorn/Electron/Video.hpp b/Machines/Acorn/Electron/Video.hpp
index eeeff4d2e..98993f4ff 100644
--- a/Machines/Acorn/Electron/Video.hpp
+++ b/Machines/Acorn/Electron/Video.hpp
@@ -81,7 +81,7 @@ class VideoOutput {
 
 		// CRT output
 		enum class OutputStage {
-			Sync, Blank, Pixels
+			Sync, Blank, Pixels, ColourBurst,
 		};
 		OutputStage output_ = OutputStage::Blank;
 		int output_length_ = 0;
@@ -148,7 +148,10 @@ class VideoOutput {
 												// _after_ position increment rather than before/instead.
 												// So it needs to be one higher. Which is baked into
 												// the constant to emphasise the all-divisible-by-8 property.
+
 		static constexpr int h_half = h_total / 2;
+		static constexpr int hburst_start = 856;
+		static constexpr int hburst_end = 896;
 
 		// Vertical timing parameters; all in terms of lines. As per the horizontal parameters above,
 		// lines begin with their first visible pixel (or the equivalent position).