Merge pull request #65 from TomHarte/OricVideoImprovements

Rearranges Oric painting logic to reduce code path complexity

Machines/Oric/Video.cpp

@@ -22,7 +22,6 @@ namespace {
 VideoOutput::VideoOutput(uint8_t *memory) :
 	_ram(memory),
 	_frame_counter(0), _counter(0),
-	_state(Sync), _cycles_in_state(0),
 	_is_graphics_mode(false),
 	_character_set_base_address(0xb400),
 	_phase(0),
@@ -54,11 +53,23 @@ void VideoOutput::run_for_cycles(int number_of_cycles)
 	// Vertical: 0–39: pixels; otherwise blank; 48–53 sync, 54–56 colour burst
 	// Horizontal: 0–223: pixels; otherwise blank; 256–259 sync
 
-	while(number_of_cycles--)
+#define clamp(action)	\
-	{
+	if(cycles_run_for <= number_of_cycles) { action; } else cycles_run_for = number_of_cycles;
-		_counter = (_counter + 1)%_counter_period;
-		int h_counter =_counter & 63;
 
+	while(number_of_cycles)
+	{
+		int h_counter =_counter & 63;
+		int cycles_run_for = 0;
+
+		if(_counter >= _v_sync_start_position && _counter < _v_sync_end_position)
+		{
+			// this is a sync line
+			cycles_run_for = _v_sync_end_position - _counter;
+			clamp(_crt->output_sync((unsigned int)(_v_sync_end_position - _v_sync_start_position) * 6));
+		}
+		else if(_counter < 224*64 && h_counter < 40)
+		{
+			// this is a pixel line
 			if(!h_counter)
 			{
 				_ink = 0xff;
@@ -66,10 +77,11 @@ void VideoOutput::run_for_cycles(int number_of_cycles)
 				_use_alternative_character_set = _use_double_height_characters = _blink_text = false;
 				set_character_set_base_address();
 				_phase += 64;
+				_pixel_target = _crt->allocate_write_area(120);
 
 				if(!_counter)
 				{
-				_phase += 128;
+					_phase += 128; // TODO: incorporate all the lines that were missed
 					_frame_counter++;
 
 					_v_sync_start_position = _next_frame_is_sixty_hertz ? PAL60VSyncStartPosition : PAL50VSyncStartPosition;
@@ -78,46 +90,30 @@ void VideoOutput::run_for_cycles(int number_of_cycles)
 				}
 			}
 
+			cycles_run_for = std::min(40 - h_counter, number_of_cycles);
+			int columns = cycles_run_for;
+			int pixel_base_address = 0xa000 + (_counter >> 6) * 40;
+			int character_base_address = 0xbb80 + (_counter >> 9) * 40;
+			uint8_t blink_mask = (_blink_text && (_frame_counter&32)) ? 0x00 : 0xff;
 
-		State new_state = Blank;
+			while(columns--)
-		if(
-			(h_counter >= 48 && h_counter <= 53) ||
-			(_counter >= _v_sync_start_position && _counter <= _v_sync_end_position)) new_state = Sync;
-		else if(h_counter >= 54 && h_counter <= 56) new_state = ColourBurst;
-		else if(_counter < 224*64 && h_counter < 40) new_state = Pixels;
-
-		if(_state != new_state)
 			{
-			switch(_state)
-			{
-				case ColourBurst:	_crt->output_colour_burst(_cycles_in_state * 6, _phase, 128);	break;
-				case Sync:			_crt->output_sync(_cycles_in_state * 6);						break;
-				case Blank:			_crt->output_blank(_cycles_in_state * 6);						break;
-				case Pixels:		_crt->output_data(_cycles_in_state * 6, 2);						break;
-			}
-			_state = new_state;
-			_cycles_in_state = 0;
-			if(_state == Pixels) _pixel_target = _crt->allocate_write_area(120);
-		}
-		_cycles_in_state++;
-
-		if(new_state == Pixels) {
 				uint8_t pixels, control_byte;
 
 				if(_is_graphics_mode && _counter < 200*64)
 				{
-				control_byte = pixels = _ram[0xa000 + (_counter >> 6) * 40 + h_counter];
+					control_byte = pixels = _ram[pixel_base_address + h_counter];
 				}
 				else
 				{
-				int address = 0xbb80 + (_counter >> 9) * 40 + h_counter;
+					int address = character_base_address + h_counter;
 					control_byte = _ram[address];
 					int line = _use_double_height_characters ? ((_counter >> 7) & 7) : ((_counter >> 6) & 7);
 					pixels = _ram[_character_set_base_address + (control_byte&127) * 8 + line];
 				}
 
 				uint8_t inverse_mask = (control_byte & 0x80) ? 0x77 : 0x00;
-			if(_blink_text && (_frame_counter&32)) pixels = 0;
+				pixels &= blink_mask;
 
 				if(control_byte & 0x60)
 				{
@@ -174,6 +170,49 @@ void VideoOutput::run_for_cycles(int number_of_cycles)
 					if(_pixel_target) _pixel_target[0] = _pixel_target[1] = _pixel_target[2] = (uint8_t)(_paper ^ inverse_mask);
 				}
 				if(_pixel_target) _pixel_target += 3;
+				h_counter++;
 			}
+
+			if(h_counter == 40)
+			{
+				_crt->output_data(40 * 6, 2);
+			}
+		}
+		else
+		{
+			// this is a blank line (or the equivalent part of a pixel line)
+			if(h_counter < 48)
+			{
+				cycles_run_for = 48 - h_counter;
+				clamp(
+					int period = (_counter < 224*64) ? 8 : 48;
+					_crt->output_blank((unsigned int)period * 6);
+				);
+			}
+			else if(h_counter < 54)
+			{
+				cycles_run_for = 54 - h_counter;
+				clamp(_crt->output_sync(6 * 6));
+			}
+			else if(h_counter < 56)
+			{
+				cycles_run_for = 56 - h_counter;
+				clamp(_crt->output_colour_burst(2 * 6, _phase, 128));
+			}
+			else
+			{
+				cycles_run_for = 64 - h_counter;
+				clamp(_crt->output_blank(8 * 6));
+			}
+		}
+
+		_counter = (_counter + cycles_run_for)%_counter_period;
+		number_of_cycles -= cycles_run_for;
 	}
 }
+
+void VideoOutput::set_character_set_base_address()
+{
+	if(_is_graphics_mode) _character_set_base_address = _use_alternative_character_set ? 0x9c00 : 0x9800;
+	else _character_set_base_address = _use_alternative_character_set ? 0xb800 : 0xb400;
+}

Machines/Oric/Video.hpp

@@ -27,22 +27,14 @@ class VideoOutput {
 		int _counter, _frame_counter;
 		int _v_sync_start_position, _v_sync_end_position, _counter_period;
 
-		// Output state
+		// Output target
-		enum State {
-			Blank, Sync, Pixels, ColourBurst
-		} _state;
-		unsigned int _cycles_in_state;
 		uint8_t *_pixel_target;
 
 		// Registers
 		uint8_t _ink, _paper;
 
 		int _character_set_base_address;
-		inline void set_character_set_base_address()
+		inline void set_character_set_base_address();
-		{
-			if(_is_graphics_mode) _character_set_base_address = _use_alternative_character_set ? 0x9c00 : 0x9800;
-			else _character_set_base_address = _use_alternative_character_set ? 0xb800 : 0xb400;
-		}
 
 		bool _is_graphics_mode;
 		bool _next_frame_is_sixty_hertz;