Overtly link line and sprite buffers.

Components/9918/Implementation/9918.cpp

@@ -56,7 +56,6 @@ Base<personality>::Base() :
 	fetch_line_buffer_ = line_buffers_.begin();
 	draw_line_buffer_ = line_buffers_.begin();
 	fetch_sprite_buffer_ = sprite_buffers_.begin();
-	draw_sprite_buffer_ = sprite_buffers_.begin();
 }
 
 template <Personality personality>
@@ -131,9 +130,8 @@ 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_);
+		fetched_sprites_ = &*fetch_sprite_buffer_;
 		fetch_sprite_buffer_->reset_sprite_collection();
 		fetch_sprite_buffer_->sprite_terminator = mode_timing_.sprite_terminator(fetch_line_buffer_->screen_mode);
 
@@ -349,6 +347,13 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 				}
 
 				this->advance(this->fetch_line_buffer_);
+				if(this->fetched_sprites_->active_sprite_slot) {
+					this->fetch_line_buffer_->sprites = this->fetched_sprites_;
+					this->fetched_sprites_ = nullptr;
+				} else {
+					this->fetch_line_buffer_->sprites = nullptr;
+					this->regress(this->fetch_sprite_buffer_);
+				}
 
 				// Establish the current screen output mode, which will be captured as a
 				// line mode momentarily.
@@ -367,7 +372,6 @@ 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_;
-				this->fetch_line_buffer_->fetched_sprites = false;
 				this->mode_timing_.maximum_visible_sprites = 4;
 				switch(this->screen_mode_) {
 					case ScreenMode::Text:
@@ -606,12 +610,6 @@ void TMS9918<personality>::run_for(const HalfCycles cycles) {
 				// -------------
 				this->output_pointer_.column = end_column;
 				if(end_column == Timing<personality>::CyclesPerLine) {
-					// Clear all sprites from this sprite buffer.
-					this->draw_sprite_buffer_->active_sprite_slot = 0;
-					// Advance to the next sprite buffer only if this one was populated by this line.
-					if(this->draw_line_buffer_->fetched_sprites) {
-						this->advance(this->draw_sprite_buffer_);
-					}
 					// Advance line buffer.
 					this->advance(this->draw_line_buffer_);
 				}

Components/9918/Implementation/9918Base.hpp

@@ -217,13 +217,19 @@ template <Personality personality> struct Base: public Storage<personality> {
 	using SpriteBufferArray = std::array<SpriteBuffer, 313>;
 	SpriteBufferArray sprite_buffers_;
 	SpriteBufferArray::iterator fetch_sprite_buffer_;
-	SpriteBufferArray::iterator draw_sprite_buffer_;
+	SpriteBuffer *fetched_sprites_ = nullptr;
 	void advance(SpriteBufferArray::iterator &iterator) {
 		++iterator;
 		if(iterator == sprite_buffers_.end()) {
 			iterator = sprite_buffers_.begin();
 		}
 	}
+	void regress(SpriteBufferArray::iterator &iterator) {
+		if(iterator == sprite_buffers_.begin()) {
+			iterator = sprite_buffers_.end();
+		}
+		--iterator;
+	}
 
 	AddressT tile_offset_ = 0;
 	uint8_t name_[4]{};

Components/9918/Implementation/Draw.hpp

@@ -14,7 +14,11 @@
 template <Personality personality>
 template <SpriteMode mode, bool double_width>
 void Base<personality>::draw_sprites(uint8_t y, int start, int end, const std::array<uint32_t, 16> &palette, int *colour_buffer) {
-	auto &buffer = *draw_sprite_buffer_;
+	if(!draw_line_buffer_->sprites) {
+		return;
+	}
+
+	auto &buffer = *draw_line_buffer_->sprites;
 	if(!buffer.active_sprite_slot) {
 		return;
 	}

Components/9918/Implementation/LineBuffer.hpp

@@ -14,6 +14,54 @@
 namespace TI::TMS {
 
 // Temporary buffers collect a representation of each line prior to pixel serialisation.
+
+struct SpriteBuffer {
+	// An active sprite is one that has been selected for composition onto
+	// _this_ line.
+	struct ActiveSprite {
+		int index = 0;		// The original in-table index of this sprite.
+		int row = 0;		// The row of the sprite that should be drawn.
+		int x = 0;			// The sprite's x position on screen.
+
+		uint8_t image[4];		// Up to four bytes of image information.
+								//
+								// In practice:
+								//
+								//	Master System mode: the four bytes of this 8x8 sprite;
+								//	TMS and Yamaha: [0] = the left half of this sprite; [1] = the right side (if 16x16 sprites enabled); [2] = colour, early-clock bit, etc.
+		int shift_position = 0;	// An offset representing how much of the image information has already been drawn.
+
+		// Yamaha helpers.
+		bool opaque() const {
+			return !(image[2] & 0x40);
+		}
+
+		/// @returns @c 0x20 if this sprite should generate collisions; @c 0x00 otherwise.
+		int collision_bit() const {
+			return ((image[2] & 0x20) | ((image[2] & 0x40) >> 1)) ^ 0x20;
+		}
+
+		// Yamaha and TMS helpers.
+		int early_clock() const {
+			return (image[2] & 0x80) >> 2;
+		}
+	} active_sprites[8];
+
+	int active_sprite_slot = 0;		// A pointer to the slot into which a new active sprite will be deposited, if required.
+	bool sprites_stopped = false;	// A special TMS feature is that a sentinel value can be used to prevent any further sprites
+									// being evaluated for display. This flag determines whether the sentinel has yet been reached.
+	uint8_t sprite_terminator = 0;
+
+#ifndef NDEBUG
+	static constexpr bool test_is_filling = true;
+#else
+	static constexpr bool test_is_filling = false;
+#endif
+	bool is_filling = false;
+
+	void reset_sprite_collection();
+};
+
 struct LineBuffer {
 	LineBuffer() {}
 
@@ -22,7 +70,7 @@ struct LineBuffer {
 	FetchMode fetch_mode = FetchMode::Text;
 	ScreenMode screen_mode = ScreenMode::Text;
 	VerticalState vertical_state = VerticalState::Blank;
-	bool fetched_sprites = false;
+	SpriteBuffer *sprites = nullptr;
 
 	// Holds the horizontal scroll position to apply to this line;
 	// of those VDPs currently implemented, affects the Master System only.
@@ -75,53 +123,6 @@ struct LineBuffer {
 	int pixel_count = 256;
 };
 
-struct SpriteBuffer {
-	// An active sprite is one that has been selected for composition onto
-	// _this_ line.
-	struct ActiveSprite {
-		int index = 0;		// The original in-table index of this sprite.
-		int row = 0;		// The row of the sprite that should be drawn.
-		int x = 0;			// The sprite's x position on screen.
-
-		uint8_t image[4];		// Up to four bytes of image information.
-								//
-								// In practice:
-								//
-								//	Master System mode: the four bytes of this 8x8 sprite;
-								//	TMS and Yamaha: [0] = the left half of this sprite; [1] = the right side (if 16x16 sprites enabled); [2] = colour, early-clock bit, etc.
-		int shift_position = 0;	// An offset representing how much of the image information has already been drawn.
-
-		// Yamaha helpers.
-		bool opaque() const {
-			return !(image[2] & 0x40);
-		}
-
-		/// @returns @c 0x20 if this sprite should generate collisions; @c 0x00 otherwise.
-		int collision_bit() const {
-			return ((image[2] & 0x20) | ((image[2] & 0x40) >> 1)) ^ 0x20;
-		}
-
-		// Yamaha and TMS helpers.
-		int early_clock() const {
-			return (image[2] & 0x80) >> 2;
-		}
-	} active_sprites[8];
-
-	int active_sprite_slot = 0;		// A pointer to the slot into which a new active sprite will be deposited, if required.
-	bool sprites_stopped = false;	// A special TMS feature is that a sentinel value can be used to prevent any further sprites
-									// being evaluated for display. This flag determines whether the sentinel has yet been reached.
-	uint8_t sprite_terminator = 0;
-
-#ifndef NDEBUG
-	static constexpr bool test_is_filling = true;
-#else
-	static constexpr bool test_is_filling = false;
-#endif
-	bool is_filling = false;
-
-	void reset_sprite_collection();
-};
-
 struct LineBufferPointer {
 	int row = 0, column = 0;
 };