From 0d8af010b6b56598a7657977e1cde1a9271b535c Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 28 Sep 2018 22:37:10 -0400
Subject: [PATCH] Takes a stab at tile reversal and vertical scrolling.

---
 Components/9918/9918.cpp                    | 19 ++++++++++++++++---
 Components/9918/Implementation/9918Base.hpp | 11 ++++++++---
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/Components/9918/9918.cpp b/Components/9918/9918.cpp
index b69eb3922..b3123e6a3 100644
--- a/Components/9918/9918.cpp
+++ b/Components/9918/9918.cpp
@@ -437,18 +437,19 @@ void TMS9918::run_for(const HalfCycles cycles) {
 							if(pixel_target_) {
 								const int pixels_left = pixels_end - output_column_;
 								const int pixel_location = output_column_ - first_pixel_column_;
+								const int reverses[2] = {0, 7};
 								for(int c = 0; c < pixels_left; ++c) {
 									const int column = (pixel_location + c) >> 3;
-									const int shift = 4 + ((pixel_location + c) & 7);
+									const int shift = 4 + (((pixel_location + c) & 7) ^ reverses[(master_system_.names[column].flags&2) >> 1]);
 									int value =
 									((
 										((master_system_.tile_graphics[column][0] << shift) & 0x800) |
 										((master_system_.tile_graphics[column][1] << (shift - 1)) & 0x400) |
 										((master_system_.tile_graphics[column][2] << (shift - 2)) & 0x200) |
-										(master_system_.tile_graphics[column][3] << (shift - 3))
+										((master_system_.tile_graphics[column][3] << (shift - 3)) & 0x100)
 									) >> 8) << 4;
 
-									pixel_target_[c] = (value << 24) | (value << 16) | (value << 8) | value;
+									pixel_target_[c] = static_cast<uint32_t>((value << 24) | (value << 16) | (value << 8) | value);
 								}
 								pixel_target_ += pixels_left;
 							}
@@ -766,6 +767,18 @@ void TMS9918::set_register(int address, uint8_t value) {
 				text_colour_ = low_write_ >> 4;
 				background_colour_ = low_write_ & 0xf;
 			break;
+
+			case 8:
+				if(is_sega_vdp(personality_)) {
+					master_system_.horizontal_scroll = low_write_;
+				}
+			break;
+
+			case 9:
+				if(is_sega_vdp(personality_)) {
+					master_system_.vertical_scroll = low_write_;
+				}
+			break;
 		}
 	} else {
 		// This is a write to the RAM pointer.
diff --git a/Components/9918/Implementation/9918Base.hpp b/Components/9918/Implementation/9918Base.hpp
index b9acf0a47..7fe0c541d 100644
--- a/Components/9918/Implementation/9918Base.hpp
+++ b/Components/9918/Implementation/9918Base.hpp
@@ -126,6 +126,9 @@ class Base {
 			} names[32];
 			uint8_t tile_graphics[32][4];
 			size_t next_column = 0;
+
+			uint8_t horizontal_scroll = 0;
+			uint8_t vertical_scroll = 0;
 		} master_system_;
 
 		enum class ScreenMode {
@@ -218,7 +221,7 @@ class Base {
 #define fetch_tile_name(column)	{\
 		size_t address = pattern_address_base + ((column) << 1);	\
 		master_system_.names[column].flags = ram_[address+1];	\
-		master_system_.names[column].offset = static_cast<size_t>((((master_system_.names[column].flags&1) << 8) | ram_[address]) << 5) + sub_row;	\
+		master_system_.names[column].offset = static_cast<size_t>((((master_system_.names[column].flags&1) << 8) | ram_[address]) << 5) + sub_row[(master_system_.names[column].flags&4) >> 2];	\
 	}
 
 #define fetch_tile(column)	{\
@@ -265,8 +268,10 @@ class Base {
 		- column n+3, tile graphic first word
 		- column n+3, tile graphic second word
 */
-			const size_t pattern_address_base = (pattern_name_address_ | size_t(0x3ff)) & static_cast<size_t>(((row_ & ~7) << 3) | 0x3800);
-			const size_t sub_row = static_cast<size_t>((row_ & 7) << 2);
+
+			const int scrolled_row = (row_ + master_system_.vertical_scroll) % 224;
+			const size_t pattern_address_base = (pattern_name_address_ | size_t(0x3ff)) & static_cast<size_t>(((scrolled_row & ~7) << 3) | 0x3800);
+			const size_t sub_row[2] = {static_cast<size_t>((scrolled_row & 7) << 2), 28 ^ static_cast<size_t>((scrolled_row & 7) << 2)};
 
 			switch(start) {
 				default: