Add sanity check on sprite fetches versus draws.

Components/9918/Implementation/9918.cpp

@@ -136,6 +136,10 @@ void Base<personality>::posit_sprite(int sprite_number, int sprite_position, uin
 		advance(fetch_sprite_buffer_);
 		fetch_sprite_buffer_->reset_sprite_collection();
 		fetch_sprite_buffer_->sprite_terminator = mode_timing_.sprite_terminator(fetch_line_buffer_->screen_mode);
+
+#ifndef NDEBUG
+		fetch_sprite_buffer_->is_filling = true;
+#endif
 	}
 
 	if(!(status_ & StatusSpriteOverflow)) {

Components/9918/Implementation/Draw.hpp

@@ -78,6 +78,8 @@ void Base<personality>::draw_sprites(uint8_t y, int start, int end, const std::a
 		return;
 	}
 
+	assert(!buffer.is_filling);
+
 	constexpr uint32_t sprite_colour_selection_masks[2] = {0x00000000, 0xffffffff};
 	constexpr int colour_masks[16] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
 	const int sprite_width = sprites_16x16_ ? 16 : 8;

Components/9918/Implementation/Fetch.hpp

@@ -281,6 +281,12 @@ class SpriteFetcher {
 			const AddressT graphic_location = base->sprite_generator_table_address_ & bits<11>(AddressT((name << 3) | sprite.row));
 			sprite.image[0] = base->ram_[graphic_location];
 			sprite.image[1] = base->ram_[graphic_location+16];
+
+#ifndef NDEBUG
+			if(slot == ((mode == SpriteMode::Mode2) ? 7 : 3)) {
+				base->fetch_sprite_buffer_->is_filling = false;
+			}
+#endif
 		}
 
 		Base<personality> *const base;

Components/9918/Implementation/LineBuffer.hpp

@@ -112,6 +112,10 @@ struct SpriteBuffer {
 									// being evaluated for display. This flag determines whether the sentinel has yet been reached.
 	uint8_t sprite_terminator = 0;
 
+#ifndef NDEBUG
+	bool is_filling = false;
+#endif
+
 	void reset_sprite_collection();
 };