Use C++20 std::numbers, std::lerp() (#7696)

* use c++20 concepts and numbers for lmms_constants.h

* replace lmms::numbers::sqrt2 with std::numbers::sqrt2

* replace lmms::numbers::e with std::numbers::e
Also replace the only use of lmms::numbers::inv_e with a local constexpr instead

* remove lmms::numbers::pi_half and lmms::numbers::pi_sqr
They were only used in one or two places each

* replace lmms::numbers::pi with std::numbers::pi

* add #include <numbers> to every file touched so far
This is probably not needed for some of these files. I'll remove those later

* Remove lmms::numbers

Rest in peace lmms::numbers::tau, my beloved

* Add missing #include <numbers>

* replace stray use of F_EPSILON with approximatelyEqual()

* make many constants inline constexpr
A lot of the remaining constants in lmms_constants.h are specific to
SaProcessor. If they are only used there, shouldn't they be in SaProcessor.h?

* ok then, it's allowed to be signed

* remove #include "lmms_constants.h" for files that don't need it
- And also move F_EPSILON into lmms_math.h
- And also add an overload for fast_rand() to specify a higher and lower bound
- And a bunch of other nonsense

* ok then, it's allowed to be inferred

* ok then, it can accept an integral

* fix typo

* appease msvc

* appease msvc again

* Replace linearInterpolate with std::lerp()

As well as time travel to undo several foolish decisions and squash tiny
commits together

* Fix msvc constexpr warnings

* Fix msvc float to double truncation warning

* Apply two suggestions from code review

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

* Apply suggestions from code review

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

* fix silly mistake

* Remove SlicerT's dependence on lmms_math.h

* Allow more type inference on fastRand() and fastPow10f()

* Apply suggestions from code review

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

* Clean up fastRand() a little bit more

---------

Co-authored-by: Dalton Messmer <messmer.dalton@gmail.com>

plugins/Compressor/CompressorControlDialog.cpp

@@ -26,6 +26,7 @@
 #include "CompressorControlDialog.h"
 #include "CompressorControls.h"
 
+#include <cmath>
 #include <QLabel>
 #include <QPainter>
 #include <QWheelEvent>
@@ -34,7 +35,6 @@
 #include "embed.h"
 #include "../Eq/EqFader.h"
 #include "GuiApplication.h"
-#include "interpolation.h"
 #include "Knob.h"
 #include "MainWindow.h"
 #include "PixmapButton.h"
@@ -437,7 +437,11 @@ void CompressorControlDialog::drawVisPixmap()
 	m_p.setPen(QPen(m_inVolAreaColor, 1));
 	for (int i = 0; i < m_compPixelMovement; ++i)
 	{
-		const int temp = linearInterpolate(m_lastPoint, m_yPoint, float(i) / float(m_compPixelMovement));
+		const int temp = std::lerp(
+			m_lastPoint,
+			m_yPoint,
+			static_cast<float>(i) / static_cast<float>(m_compPixelMovement)
+		);
 		m_p.drawLine(m_windowSizeX-m_compPixelMovement+i, temp, m_windowSizeX-m_compPixelMovement+i, m_windowSizeY);
 	}
 
@@ -449,7 +453,11 @@ void CompressorControlDialog::drawVisPixmap()
 	m_p.setPen(QPen(m_outVolAreaColor, 1));
 	for (int i = 0; i < m_compPixelMovement; ++i)
 	{
-		const int temp = linearInterpolate(m_lastPoint+m_lastGainPoint, m_yPoint+m_yGainPoint, float(i) / float(m_compPixelMovement));
+		const int temp = std::lerp(
+			m_lastPoint + m_lastGainPoint,
+			m_yPoint + m_yGainPoint,
+			static_cast<float>(i) / static_cast<float>(m_compPixelMovement)
+		);
 		m_p.drawLine(m_windowSizeX-m_compPixelMovement+i, temp, m_windowSizeX-m_compPixelMovement+i, m_windowSizeY);
 	}
 
@@ -512,7 +520,7 @@ void CompressorControlDialog::redrawKnee()
 		// Draw knee curve using many straight lines.
 		for (int i = 0; i < COMP_KNEE_LINES; ++i)
 		{
-			newPoint[0] = linearInterpolate(kneePoint1, kneePoint2X, (i + 1) / (float)COMP_KNEE_LINES);
+			newPoint[0] = std::lerp(kneePoint1, kneePoint2X, (i + 1) / static_cast<float>(COMP_KNEE_LINES));
 
 			const float temp = newPoint[0] - thresholdVal + kneeVal;
 			newPoint[1] = (newPoint[0] + (actualRatio - 1) * temp * temp / (4 * kneeVal));