Convert .tgs with go libraries (and cgo) (telegram) (#1569)

This commit adds support for go/cgo tgs conversion when building with the -tags `cgo`
The default binaries are still "pure" go and uses the old way of converting.

* Move lottie_convert.py conversion code to its own file

* Add optional libtgsconverter

* Update vendor

* Apply suggestions from code review

* Update bridge/helper/libtgsconverter.go

Co-authored-by: Wim <wim@42.be>

1 files changed, 124 insertions, 0 deletions

diff --git a/vendor/github.com/Benau/go_rlottie/vector_vinterpolator.cpp b/vendor/github.com/Benau/go_rlottie/vector_vinterpolator.cpp
new file mode 100644
index 00000000..89e462a1
--- /dev/null
+++ b/vendor/github.com/Benau/go_rlottie/vector_vinterpolator.cpp
@@ -0,0 +1,124 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "vector_vinterpolator.h"
+#include <cmath>
+
+V_BEGIN_NAMESPACE
+
+#define NEWTON_ITERATIONS 4
+#define NEWTON_MIN_SLOPE 0.02
+#define SUBDIVISION_PRECISION 0.0000001
+#define SUBDIVISION_MAX_ITERATIONS 10
+
+const float VInterpolator::kSampleStepSize =
+    1.0f / float(VInterpolator::kSplineTableSize - 1);
+
+void VInterpolator::init(float aX1, float aY1, float aX2, float aY2)
+{
+    mX1 = aX1;
+    mY1 = aY1;
+    mX2 = aX2;
+    mY2 = aY2;
+
+    if (mX1 != mY1 || mX2 != mY2) CalcSampleValues();
+}
+
+/*static*/ float VInterpolator::CalcBezier(float aT, float aA1, float aA2)
+{
+    // use Horner's scheme to evaluate the Bezier polynomial
+    return ((A(aA1, aA2) * aT + B(aA1, aA2)) * aT + C(aA1)) * aT;
+}
+
+void VInterpolator::CalcSampleValues()
+{
+    for (int i = 0; i < kSplineTableSize; ++i) {
+        mSampleValues[i] = CalcBezier(float(i) * kSampleStepSize, mX1, mX2);
+    }
+}
+
+float VInterpolator::GetSlope(float aT, float aA1, float aA2)
+{
+    return 3.0f * A(aA1, aA2) * aT * aT + 2.0f * B(aA1, aA2) * aT + C(aA1);
+}
+
+float VInterpolator::value(float aX) const
+{
+    if (mX1 == mY1 && mX2 == mY2) return aX;
+
+    return CalcBezier(GetTForX(aX), mY1, mY2);
+}
+
+float VInterpolator::GetTForX(float aX) const
+{
+    // Find interval where t lies
+    float              intervalStart = 0.0;
+    const float*       currentSample = &mSampleValues[1];
+    const float* const lastSample = &mSampleValues[kSplineTableSize - 1];
+    for (; currentSample != lastSample && *currentSample <= aX;
+         ++currentSample) {
+        intervalStart += kSampleStepSize;
+    }
+    --currentSample;  // t now lies between *currentSample and *currentSample+1
+
+    // Interpolate to provide an initial guess for t
+    float dist =
+        (aX - *currentSample) / (*(currentSample + 1) - *currentSample);
+    float guessForT = intervalStart + dist * kSampleStepSize;
+
+    // Check the slope to see what strategy to use. If the slope is too small
+    // Newton-Raphson iteration won't converge on a root so we use bisection
+    // instead.
+    float initialSlope = GetSlope(guessForT, mX1, mX2);
+    if (initialSlope >= NEWTON_MIN_SLOPE) {
+        return NewtonRaphsonIterate(aX, guessForT);
+    } else if (initialSlope == 0.0) {
+        return guessForT;
+    } else {
+        return BinarySubdivide(aX, intervalStart,
+                               intervalStart + kSampleStepSize);
+    }
+}
+
+float VInterpolator::NewtonRaphsonIterate(float aX, float aGuessT) const
+{
+    // Refine guess with Newton-Raphson iteration
+    for (int i = 0; i < NEWTON_ITERATIONS; ++i) {
+        // We're trying to find where f(t) = aX,
+        // so we're actually looking for a root for: CalcBezier(t) - aX
+        float currentX = CalcBezier(aGuessT, mX1, mX2) - aX;
+        float currentSlope = GetSlope(aGuessT, mX1, mX2);
+
+        if (currentSlope == 0.0) return aGuessT;
+
+        aGuessT -= currentX / currentSlope;
+    }
+
+    return aGuessT;
+}
+
+float VInterpolator::BinarySubdivide(float aX, float aA, float aB) const
+{
+    float currentX;
+    float currentT;
+    int   i = 0;
+
+    do {
+        currentT = aA + (aB - aA) / 2.0f;
+        currentX = CalcBezier(currentT, mX1, mX2) - aX;
+
+        if (currentX > 0.0) {
+            aB = currentT;
+        } else {
+            aA = currentT;
+        }
+    } while (fabs(currentX) > SUBDIVISION_PRECISION &&
+             ++i < SUBDIVISION_MAX_ITERATIONS);
+
+    return currentT;
+}
+
+V_END_NAMESPACE