From dd5b4b484a4b43940b6b9a8f2327f4390905a5b5 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 7 Jan 2023 14:34:33 -0500
Subject: [PATCH] Avoid double responsibility for state.

---
 Components/9918/Implementation/9918.cpp     |  2 +-
 Components/9918/Implementation/9918Base.hpp | 24 +++++++--------------
 2 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/Components/9918/Implementation/9918.cpp b/Components/9918/Implementation/9918.cpp
index 79221be58..5ebe4761b 100644
--- a/Components/9918/Implementation/9918.cpp
+++ b/Components/9918/Implementation/9918.cpp
@@ -266,7 +266,7 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 				LineBuffer &next_line_buffer = this->line_buffers_[this->write_pointer_.row];
 
 				// Establish the output mode for the next line.
-				this->set_current_screen_mode();
+				this->screen_mode_ = this->current_screen_mode();
 
 				// Based on the output mode, pick a line mode.
 				next_line_buffer.first_pixel_output_column = Timing<personality>::FirstPixelCycle;
diff --git a/Components/9918/Implementation/9918Base.hpp b/Components/9918/Implementation/9918Base.hpp
index 495247913..6eba4be8d 100644
--- a/Components/9918/Implementation/9918Base.hpp
+++ b/Components/9918/Implementation/9918Base.hpp
@@ -298,43 +298,35 @@ template <Personality personality> struct Base {
 		size_t sprite_generator_table_address;
 	} master_system_;
 
-	void set_current_screen_mode() {
+	ScreenMode current_screen_mode() const {
 		if(blank_display_) {
-			screen_mode_ = ScreenMode::Blank;
-			return;
+			return ScreenMode::Blank;
 		}
 
 		if constexpr (is_sega_vdp(personality)) {
 			if(master_system_.mode4_enable) {
-				screen_mode_ = ScreenMode::SMSMode4;
-				mode_timing_.maximum_visible_sprites = 8;
-				return;
+				return ScreenMode::SMSMode4;
 			}
 		}
 
-		mode_timing_.maximum_visible_sprites = 4;
 		if(!mode1_enable_ && !mode2_enable_ && !mode3_enable_) {
-			screen_mode_ = ScreenMode::ColouredText;
-			return;
+			return ScreenMode::ColouredText;
 		}
 
 		if(mode1_enable_ && !mode2_enable_ && !mode3_enable_) {
-			screen_mode_ = ScreenMode::Text;
-			return;
+			return ScreenMode::Text;
 		}
 
 		if(!mode1_enable_ && mode2_enable_ && !mode3_enable_) {
-			screen_mode_ = ScreenMode::Graphics;
-			return;
+			return ScreenMode::Graphics;
 		}
 
 		if(!mode1_enable_ && !mode2_enable_ && mode3_enable_) {
-			screen_mode_ = ScreenMode::MultiColour;
-			return;
+			return ScreenMode::MultiColour;
 		}
 
 		// TODO: undocumented TMS modes.
-		screen_mode_ = ScreenMode::Blank;
+		return ScreenMode::Blank;
 	}
 
 	void do_external_slot(int access_column) {