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>

vendor/github.com/sizeofint/webpanimation/dsp_ssim.c

@@ -0,0 +1,159 @@
+// Copyright 2017 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// distortion calculation
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include <assert.h>
+#include <stdlib.h>  // for abs()
+
+#include "dsp_dsp.h"
+
+#if !defined(WEBP_REDUCE_SIZE)
+
+//------------------------------------------------------------------------------
+// SSIM / PSNR
+
+// hat-shaped filter. Sum of coefficients is equal to 16.
+static const uint32_t kWeight[2 * VP8_SSIM_KERNEL + 1] = {
+  1, 2, 3, 4, 3, 2, 1
+};
+static const uint32_t kWeightSum = 16 * 16;   // sum{kWeight}^2
+
+static WEBP_INLINE double SSIMCalculation(
+    const VP8DistoStats* const stats, uint32_t N  /*num samples*/) {
+  const uint32_t w2 =  N * N;
+  const uint32_t C1 = 20 * w2;
+  const uint32_t C2 = 60 * w2;
+  const uint32_t C3 = 8 * 8 * w2;   // 'dark' limit ~= 6
+  const uint64_t xmxm = (uint64_t)stats->xm * stats->xm;
+  const uint64_t ymym = (uint64_t)stats->ym * stats->ym;
+  if (xmxm + ymym >= C3) {
+    const int64_t xmym = (int64_t)stats->xm * stats->ym;
+    const int64_t sxy = (int64_t)stats->xym * N - xmym;    // can be negative
+    const uint64_t sxx = (uint64_t)stats->xxm * N - xmxm;
+    const uint64_t syy = (uint64_t)stats->yym * N - ymym;
+    // we descale by 8 to prevent overflow during the fnum/fden multiply.
+    const uint64_t num_S = (2 * (uint64_t)(sxy < 0 ? 0 : sxy) + C2) >> 8;
+    const uint64_t den_S = (sxx + syy + C2) >> 8;
+    const uint64_t fnum = (2 * xmym + C1) * num_S;
+    const uint64_t fden = (xmxm + ymym + C1) * den_S;
+    const double r = (double)fnum / fden;
+    assert(r >= 0. && r <= 1.0);
+    return r;
+  }
+  return 1.;   // area is too dark to contribute meaningfully
+}
+
+double VP8SSIMFromStats(const VP8DistoStats* const stats) {
+  return SSIMCalculation(stats, kWeightSum);
+}
+
+double VP8SSIMFromStatsClipped(const VP8DistoStats* const stats) {
+  return SSIMCalculation(stats, stats->w);
+}
+
+static double SSIMGetClipped_C(const uint8_t* src1, int stride1,
+                               const uint8_t* src2, int stride2,
+                               int xo, int yo, int W, int H) {
+  VP8DistoStats stats = { 0, 0, 0, 0, 0, 0 };
+  const int ymin = (yo - VP8_SSIM_KERNEL < 0) ? 0 : yo - VP8_SSIM_KERNEL;
+  const int ymax = (yo + VP8_SSIM_KERNEL > H - 1) ? H - 1
+                                                  : yo + VP8_SSIM_KERNEL;
+  const int xmin = (xo - VP8_SSIM_KERNEL < 0) ? 0 : xo - VP8_SSIM_KERNEL;
+  const int xmax = (xo + VP8_SSIM_KERNEL > W - 1) ? W - 1
+                                                  : xo + VP8_SSIM_KERNEL;
+  int x, y;
+  src1 += ymin * stride1;
+  src2 += ymin * stride2;
+  for (y = ymin; y <= ymax; ++y, src1 += stride1, src2 += stride2) {
+    for (x = xmin; x <= xmax; ++x) {
+      const uint32_t w = kWeight[VP8_SSIM_KERNEL + x - xo]
+                       * kWeight[VP8_SSIM_KERNEL + y - yo];
+      const uint32_t s1 = src1[x];
+      const uint32_t s2 = src2[x];
+      stats.w   += w;
+      stats.xm  += w * s1;
+      stats.ym  += w * s2;
+      stats.xxm += w * s1 * s1;
+      stats.xym += w * s1 * s2;
+      stats.yym += w * s2 * s2;
+    }
+  }
+  return VP8SSIMFromStatsClipped(&stats);
+}
+
+static double SSIMGet_C(const uint8_t* src1, int stride1,
+                        const uint8_t* src2, int stride2) {
+  VP8DistoStats stats = { 0, 0, 0, 0, 0, 0 };
+  int x, y;
+  for (y = 0; y <= 2 * VP8_SSIM_KERNEL; ++y, src1 += stride1, src2 += stride2) {
+    for (x = 0; x <= 2 * VP8_SSIM_KERNEL; ++x) {
+      const uint32_t w = kWeight[x] * kWeight[y];
+      const uint32_t s1 = src1[x];
+      const uint32_t s2 = src2[x];
+      stats.xm  += w * s1;
+      stats.ym  += w * s2;
+      stats.xxm += w * s1 * s1;
+      stats.xym += w * s1 * s2;
+      stats.yym += w * s2 * s2;
+    }
+  }
+  return VP8SSIMFromStats(&stats);
+}
+
+#endif  // !defined(WEBP_REDUCE_SIZE)
+
+//------------------------------------------------------------------------------
+
+#if !defined(WEBP_DISABLE_STATS)
+static uint32_t AccumulateSSE_C(const uint8_t* src1,
+                                const uint8_t* src2, int len) {
+  int i;
+  uint32_t sse2 = 0;
+  assert(len <= 65535);  // to ensure that accumulation fits within uint32_t
+  for (i = 0; i < len; ++i) {
+    const int32_t diff = src1[i] - src2[i];
+    sse2 += diff * diff;
+  }
+  return sse2;
+}
+#endif
+
+//------------------------------------------------------------------------------
+
+#if !defined(WEBP_REDUCE_SIZE)
+VP8SSIMGetFunc VP8SSIMGet;
+VP8SSIMGetClippedFunc VP8SSIMGetClipped;
+#endif
+#if !defined(WEBP_DISABLE_STATS)
+VP8AccumulateSSEFunc VP8AccumulateSSE;
+#endif
+
+extern void VP8SSIMDspInitSSE2(void);
+
+WEBP_DSP_INIT_FUNC(VP8SSIMDspInit) {
+#if !defined(WEBP_REDUCE_SIZE)
+  VP8SSIMGetClipped = SSIMGetClipped_C;
+  VP8SSIMGet = SSIMGet_C;
+#endif
+
+#if !defined(WEBP_DISABLE_STATS)
+  VP8AccumulateSSE = AccumulateSSE_C;
+#endif
+
+  if (VP8GetCPUInfo != NULL) {
+#if defined(WEBP_USE_SSE2)
+    if (VP8GetCPUInfo(kSSE2)) {
+      VP8SSIMDspInitSSE2();
+    }
+#endif
+  }
+}