Rework aspect ratio calculations.

They are now based on signal timings rather than pixels, as it
didn't make a lot of sense to do things with pixels.

Now handles all 240i/240p/480i/480p modes without any special
casing.

Despite the diffrent equaions, this should result in the exact same aspect
ratio as the previous code.

Source/Core/Core/HW/VideoInterface.cpp

@@ -472,34 +472,90 @@ static u32 GetTicksPerOddField()
 	return GetTicksPerHalfLine() * GetHalfLinesPerOddField();
 }
 
+// Get the aspect ratio of VI's active area.
 float GetAspectRatio()
 {
-	u32 multiplier = static_cast<u32>(m_PictureConfiguration.STD / m_PictureConfiguration.WPL);
-	int height = (multiplier * m_VerticalTimingRegister.ACV);
-	int width = ((2 * m_HTiming0.HLW) - (m_HTiming0.HLW - m_HTiming1.HBS640)
-		- m_HTiming1.HBE640);
-	float pixelAR;
-	if (m_DisplayControlRegister.FMT == 1)
+	// The picture of a PAL/NTSC TV signal is defined to have a 4:3 aspect ratio,
+	// but it's only 4:3 if the picture fill the entire active area.
+	// All games configure VideoInterface to add padding in both the horizontal and vertical
+	// directions and most games also do a slight horizontal scale.
+	// This means that XFB never fills the entire active area and is therefor almost never 4:3
+
+	// To work out the correct aspect ratio of the XFB, we need to know how VideoInterface's
+	// currently configured active area compares to the active area of a stock PAL or NTSC
+	// signal (which would be 4:3)
+
+	// This function only deals with standard aspect ratios. For widescreen aspect ratios,
+	// multiply the result by 1.33333..
+
+	// 1. Get our active area in BT.601 samples (more or less pixels)
+	int active_lines = m_VerticalTimingRegister.ACV;
+	int active_width_samples = (m_HTiming0.HLW + m_HTiming1.HBS640 - m_HTiming1.HBE640);
+
+	// 2. TVs are analog and don't have pixels. So we convert to seconds.
+	float tick_length = (1.0f / SystemTimers::GetTicksPerSecond());
+	float vertical_period = tick_length * GetTicksPerField();
+	float horizontal_period= tick_length * GetTicksPerHalfLine() * 2;
+	float vertical_active_area = active_lines * horizontal_period;
+	float horizontal_active_area = tick_length * GetTicksPerSample() * active_width_samples;
+
+	// We are approximating the horizontal/vertical flyback transformers that control the
+	// position of the election beam on the screen. Our flyback transformers create a
+	// perfect Sawtooth wave, with a smooth rise and a fall that takes zero time.
+	// For more accurate emulation of video signals out of the 525 or 625 line standards,
+	// it might be necessary to emulate a less precise flyback transformer with more flaws.
+	// But those modes aren't officially supported by TVs anyway and could behave differently
+	// on different TVs.
+
+	// 3. Calculate the ratio of active time to total time for VI's active area
+	float vertical_active_ratio = vertical_active_area / vertical_period;
+	float horizontal_active_ratio = horizontal_active_area / horizontal_period;
+
+	// 4. And then scale the ratios to typical PAL/NTSC signals.
+	//    NOTE: With the exception of selecting between PAL-M and NTSC color encoding on Brazilian
+	//          GameCubes, the FMT field doesn't actually do anything on real hardware. But
+	//          Nintendo's SDK always sets it appropriately to match the number of lines.
+	if (m_DisplayControlRegister.FMT == 1) // 625 line TV (PAL)
 	{
-		//PAL active frame is 702*576
-		//In square pixels, 1024*576 is 16:9, and 768*576 is 4:3
-		//Therefore a 16:9 TV would have a "pixel" aspect ratio of 1024/702
-		//Similarly a 4:3 TV would have a ratio of 768/702
-		pixelAR = 768.0f / 702.0f;
+		// PAL defines the horizontal active area as 52us of the 64us line.
+		// BT.470-6 defines the blanking period as 12.0us +0.0 -0.3 [table on page 5]
+		horizontal_active_ratio *= 64.0f / 52.0f;
+		// PAL defines the vertical active area as 576 of 625 lines.
+		vertical_active_ratio *= 625.0f / 576.0f;
+		// TODO: Should PAL60 games go through the 625 or 525 line codepath?
+		//       The resulting aspect ratio is close, but not identical.
 	}
-	else
-	{
-		//NTSC active frame is 710.85*486
-		//In square pixels, 864*486 is 16:9, and 648*486 is 4:3
-		//Therefore a 16:9 TV would have a "pixel" aspect ratio of 864/710.85
-		//Similarly a 4:3 TV would have a ratio of 648/710.85
-		pixelAR = 648.0f / 710.85f;
-	}
-	if (width == 0 || height == 0)
+	else // 525 line TV (NTSC or PAL-M)
 	{
-		return 4.0f / 3.0f;
+		// The NTSC standard doesn't define it's active area very well.
+		// The line is 63.55555..us long, which is derived from 1.001 / (30 * 525)
+		// but the blanking area is defined with a large amount of slack in the SMPTE 170M-2004
+		// standard, 10.7us +0.3 -0.2 [derived from table on page 9]
+		// The BT.470-6 standard provides a different number of 10.9us +/- 0.2 [table on page 5]
+		// This results in an active area between 52.5555us and 53.05555us
+		// Lots of different numbers float around the Internet including:
+		//   * 52.655555.. us -- http://web.archive.org/web/20140218044518/http://lipas.uwasa.fi/~f76998/video/conversion/
+		//   * 52.66 us -- http://www.ni.com/white-paper/4750/en/
+		//   * 52.6 us -- http://web.mit.edu/6.111/www/f2008/handouts/L12.pdf
+		//
+		// None of these website provide primary sources for their numbers, back in the days of
+		// analog, TV signal timings were not that precise to start with and it never got standardized
+		// during the move to digital.
+		// We are just going to use 52.655555.. as most other numbers on the Internet appear to be a
+		// simplification of it. 53.655555.. is a blanking period of 10.9us, matching the BT.470-6 standard
+		// and within tolerance of the SMPTE 170M-2004 standard.
+		horizontal_active_ratio *= 63.555555f / 52.655555f;
+		// Even 486 active lines isn't completely agreed upon.
+		// Depending on how you count the two half lines you could get 485 or 484
+		vertical_active_ratio *= 525.0f / 486.0f;
 	}
-	return ((float)width / (float)height) * pixelAR;
+
+	// 5. Calculate the final ratio and scale to 4:3
+	float ratio = horizontal_active_ratio / vertical_active_ratio;
+	if (std::isnormal(ratio))	// Check we have a sane ratio and haven't propagated any infs/nans/zeros
+		return ratio * (4.0f / 3.0f); // Scale to 4:3
+	else
+		return (4.0f / 3.0f); // VI isn't initialized correctly, just return 4:3 instead
 }
 
 // This function updates:
@@ -561,9 +617,14 @@ void UpdateParameters()
 	TargetRefreshRate = lround(2.0 * SystemTimers::GetTicksPerSecond() / (GetTicksPerEvenField() + GetTicksPerOddField()));
 }
 
+u32 GetTicksPerSample()
+{
+	return 2 * SystemTimers::GetTicksPerSecond() / s_clock_freqs[m_Clock];
+}
+
 u32 GetTicksPerHalfLine()
 {
-	return 2 * SystemTimers::GetTicksPerSecond() / s_clock_freqs[m_Clock] * m_HTiming0.HLW;
+	return GetTicksPerSample() * m_HTiming0.HLW;
 }
 
 

Source/Core/Core/HW/VideoInterface.h

@@ -330,9 +330,11 @@ union UVIHorizontalStepping
 	// Change values pertaining to video mode
 	void UpdateParameters();
 
+	u32 GetTicksPerSample();
 	u32 GetTicksPerHalfLine();
 	u32 GetTicksPerField();
 
-	//For VI Scaling and Aspect Ratio Correction
+	// Get the aspect ratio of VI's active area.
+	// This function only deals with standard aspect ratios. For widescreen aspect ratios, multiply the result by 1.33333..
 	float GetAspectRatio();
 }