Permitted a wider error window on vertical sync, tidied things up a little and started trying to move towards full implementation of the OpenGL contract.

Machines/Atari2600/Atari2600.cpp

@@ -33,7 +33,7 @@ void Machine::setup_output(float aspect_ratio)
 
 	// this is the NTSC phase offset function; see below for PAL
 	_crt->set_composite_sampling_function(
-		"float composite_sample(usampler2D texID, vec2 coordinate, vec2 iCoordinate, float phase, float amplitude)\n"
+		"float composite_sample(usampler2D texID, vec2 coordinate, vec2 iCoordinate, float phase, float amplitude)"
 		"{"
 			"uint c = texture(texID, coordinate).r;"
 			"uint y = (c >> 1) & 7u;"
@@ -49,14 +49,14 @@ void Machine::switch_region()
 {
 	// the PAL function
 	_crt->set_composite_sampling_function(
-		"float composite_sample(usampler2D texID, vec2 coordinate, vec2 iCoordinate, float phase, float amplitude)\n"
+		"float composite_sample(usampler2D texID, vec2 coordinate, vec2 iCoordinate, float phase, float amplitude)"
 		"{"
 			"uint c = texture(texID, coordinate).r;"
 			"uint y = (c >> 1) & 7u;"
 			"uint iPhase = (c >> 4);"
 
 			"float phaseOffset = (0.5 + 2.0 * (float(iPhase&1u) - 0.5) * (float((iPhase >> 1) + (iPhase&1u)) / 14.0));"
-			"return (float(y) / 7.0) * (1.0 - amplitude) + step(2, iPhase) * step(iPhase, 13) * amplitude * cos(phase + 6.283185308 * phaseOffset);"
+			"return (float(y) / 7.0) * (1.0 - amplitude) + step(4, (iPhase + 2u) & 15u) * amplitude * cos(phase + 6.283185308 * phaseOffset);"
 		"}");
 	_crt->set_new_timing(228, 312, Outputs::CRT::ColourSpace::YUV, 228, 1);
 }

Outputs/CRT/CRT.cpp

@@ -38,8 +38,8 @@ void CRT::set_new_timing(unsigned int cycles_per_line, unsigned int height_of_di
 	_sync_capacitor_charge_threshold = (int)(syncCapacityLineChargeThreshold * _cycles_per_line);
 
 	// create the two flywheels
-	_horizontal_flywheel	= std::unique_ptr<Flywheel>(new Flywheel(_cycles_per_line, (millisecondsHorizontalRetraceTime * _cycles_per_line) >> 6));
+	_horizontal_flywheel	= std::unique_ptr<Flywheel>(new Flywheel(_cycles_per_line, (millisecondsHorizontalRetraceTime * _cycles_per_line) >> 6, _cycles_per_line >> 6));
-	_vertical_flywheel		= std::unique_ptr<Flywheel>(new Flywheel(_cycles_per_line * height_of_display, scanlinesVerticalRetraceTime * _cycles_per_line));
+	_vertical_flywheel		= std::unique_ptr<Flywheel>(new Flywheel(_cycles_per_line * height_of_display, scanlinesVerticalRetraceTime * _cycles_per_line, (_cycles_per_line * height_of_display) >> 3));
 
 	// figure out the divisor necessary to get the horizontal flywheel into a 16-bit range
 	unsigned int real_clock_scan_period = (_cycles_per_line * height_of_display) / (_time_multiplier * _common_output_divisor);

Outputs/CRT/Internals/CRTOpenGL.cpp

@@ -325,28 +325,47 @@ void OpenGLOutputBuilder::draw_frame(unsigned int output_width, unsigned int out
 	glViewport(0, 0, (GLsizei)output_width, (GLsizei)output_height);
 	glClear(GL_COLOR_BUFFER_BIT);
 
+	glActiveTexture(pixel_accumulation_texture_unit);
+	framebuffer->bind_texture();
 	framebuffer->draw((float)output_width / (float)output_height);
 
 	_fence = glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
 	_output_mutex->unlock();
 }
 
+void OpenGLOutputBuilder::reset_all_OpenGL_state()
+{
+	composite_input_shader_program = nullptr;
+	composite_separation_filter_program = nullptr;
+	composite_y_filter_shader_program = nullptr;
+	composite_chrominance_filter_shader_program = nullptr;
+	rgb_input_shader_program = nullptr;
+	rgb_filter_shader_program = nullptr;
+	output_shader_program = nullptr;
+	framebuffer = nullptr;
+}
+
 void OpenGLOutputBuilder::set_openGL_context_will_change(bool should_delete_resources)
 {
+	_output_mutex->lock();
+	reset_all_OpenGL_state();
+	_output_mutex->unlock();
 }
 
 void OpenGLOutputBuilder::set_composite_sampling_function(const char *shader)
 {
 	_output_mutex->lock();
 	_composite_shader = strdup(shader);
-	output_shader_program = nullptr;
+	reset_all_OpenGL_state();
-	framebuffer = nullptr;
 	_output_mutex->unlock();
 }
 
 void OpenGLOutputBuilder::set_rgb_sampling_function(const char *shader)
 {
+	_output_mutex->lock();
 	_rgb_shader = strdup(shader);
+	reset_all_OpenGL_state();
+	_output_mutex->unlock();
 }
 
 #pragma mark - Program compilation

Outputs/CRT/Internals/CRTOpenGL.hpp

@@ -85,6 +85,9 @@ class OpenGLOutputBuilder {
 		void set_timing_uniforms();
 		void set_colour_space_uniforms();
 
+		void establish_OpenGL_state();
+		void reset_all_OpenGL_state();
+
 	public:
 		OpenGLOutputBuilder(unsigned int buffer_depth);
 		~OpenGLOutputBuilder();

Outputs/CRT/Internals/Flywheel.hpp

@@ -27,13 +27,13 @@ struct Flywheel
 		Constructs an instance of @c Flywheel.
 
 		@param standard_period The expected amount of time between one synchronisation and the next.
-
 		@param retrace_time The amount of time it takes to complete a retrace.
+		@param sync_error_window The permitted deviation of sync timings from the norm.
 	*/
-	Flywheel(unsigned int standard_period, unsigned int retrace_time) :
+	Flywheel(unsigned int standard_period, unsigned int retrace_time, unsigned int sync_error_window) :
 		_standard_period(standard_period),
 		_retrace_time(retrace_time),
-		_sync_error_window(standard_period >> 7),
+		_sync_error_window(sync_error_window),
 		_counter(0),
 		_expected_next_sync(standard_period),
 		_counter_before_retrace(standard_period - retrace_time),