diff --git a/Machines/Atari2600/TIA.cpp b/Machines/Atari2600/TIA.cpp
index 984500b6b..855975d8f 100644
--- a/Machines/Atari2600/TIA.cpp
+++ b/Machines/Atari2600/TIA.cpp
@@ -132,6 +132,11 @@ TIA::TIA() :
 	collision_buffer_.resize(160);
 }
 
+TIA::TIA(std::function<void(uint8_t *output_buffer)> line_end_function) : TIA()
+{
+	line_end_function_ = line_end_function;
+}
+
 void TIA::set_output_mode(Atari2600::TIA::OutputMode output_mode)
 {
 	// this is the NTSC phase offset function; see below for PAL
@@ -402,6 +407,7 @@ void TIA::output_for_cycles(int number_of_cycles)
 
 	if(!output_cursor)
 	{
+		if(line_end_function_) line_end_function_(collision_buffer_.data());
 		memset(collision_buffer_.data(), 0, 160);	// sizeof(collision_buffer_)
 		horizontal_blank_extend_ = false;
 	}
@@ -660,14 +666,10 @@ void TIA::draw_player(Player &player, CollisionType collision_identity, const in
 				if(position < 16 && player.copy_flags&1)
 				{
 					next_copy = 16;
-				}
-				else
-				if(position < 32 && player.copy_flags&2)
+				} else if(position < 32 && player.copy_flags&2)
 				{
 					next_copy = 32;
-				}
-				else
-				if(position < 64 && player.copy_flags&4)
+				} else if(position < 64 && player.copy_flags&4)
 				{
 					next_copy = 64;
 				}
diff --git a/Machines/Atari2600/TIA.hpp b/Machines/Atari2600/TIA.hpp
index 495c8431e..dde5e06dd 100644
--- a/Machines/Atari2600/TIA.hpp
+++ b/Machines/Atari2600/TIA.hpp
@@ -19,6 +19,11 @@ class TIA {
 		TIA();
 		~TIA();
 
+		// The supplied hook is for unit testing only; if instantiated with a line_end_function then it will
+		// be called with the latest collision buffer upon the conclusion of each line. What's a collision
+		// buffer? It's an implementation detail. If you're not writing a unit test, leave it alone.
+		TIA(std::function<void(uint8_t *output_buffer)> line_end_function);
+
 		enum class OutputMode {
 			NTSC, PAL
 		};
@@ -74,6 +79,7 @@ class TIA {
 
 	private:
 		std::shared_ptr<Outputs::CRT::CRT> crt_;
+		std::function<void(uint8_t *output_buffer)> line_end_function_;
 
 		// the master counter; counts from 0 to 228 with all visible pixels being in the final 160
 		int horizontal_counter_;
@@ -138,6 +144,8 @@ class TIA {
 			int pixel_position;
 			int output_delay;
 			bool graphic_delay;
+
+			Player() : size(0), copy_flags(0), graphic{0, 0}, reverse_mask(false), pixel_position(32), output_delay(0), graphic_delay(false) {}
 		} player_[2];
 
 		// missile state