1 files changed, 144 insertions, 0 deletions
diff --git a/src/interpolator.c b/src/interpolator.c
new file mode 100644
index 0000000..e47fbe3
--- /dev/null
+++ b/src/interpolator.c
@@ -0,0 +1,144 @@
+/*
+  An LV2 plugin to generate a smooth audio signal from a control source.
+  Copyright 2011 David Robillard
+  Copyright 2002 Mike Rawes
+
+  This is free software: you can redistribute it and/or modify it
+  under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This software is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this software.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <stdlib.h>
+#include "lv2/lv2plug.in/ns/lv2core/lv2.h"
+
+#define INTERPOLATOR_INPUT  0
+#define INTERPOLATOR_OUTPUT 1
+
+/**
+   Mutated spline interpolator using only two previous samples and one next.
+   @param interval Normalised time interval between inteprolated sample and p0
+   @param p1 Sample two previous to interpolated one
+   @param p0 Previous sample to interpolated one
+   @param n0 Sample following interpolated one
+   @return Interpolated sample.
+*/
+static inline float
+interpolate(float interval,
+            float p1,
+            float p0,
+            float n0)
+{
+	return p0 + 0.5f * interval * (n0 - p1 +
+	                   interval * (4.0f * n0 + 2.0f * p1 - 5.0f * p0 - n0 +
+	                   interval * (3.0f * (p0 - n0) - p1 + n0)));
+}
+
+typedef struct {
+	const float* input;
+	float*       output;
+	float        p1;
+	float        p0;
+} Interpolator;
+
+static void
+cleanup(LV2_Handle instance)
+{
+	free(instance);
+}
+
+static void
+connect_port(LV2_Handle instance,
+             uint32_t   port,
+             void*      data)
+{
+	Interpolator* plugin = (Interpolator*)instance;
+
+	switch (port) {
+	case INTERPOLATOR_INPUT:
+		plugin->input = (const float*)data;
+		break;
+	case INTERPOLATOR_OUTPUT:
+		plugin->output = (float*)data;
+		break;
+	}
+}
+
+static LV2_Handle
+instantiate(const LV2_Descriptor*     descriptor,
+            double                    sample_rate,
+            const char*               bundle_path,
+            const LV2_Feature* const* features)
+{
+	Interpolator* plugin = (Interpolator*)malloc(sizeof(Interpolator));
+	if (!plugin) {
+		return NULL;
+	}
+
+	return (LV2_Handle)plugin;
+}
+
+static void
+activate(LV2_Handle instance)
+{
+	Interpolator* plugin = (Interpolator*)instance;
+
+	plugin->p1 = 0.0f;
+	plugin->p0 = 0.0f;
+}
+
+static void
+run(LV2_Handle instance,
+    uint32_t   sample_count)
+{
+	Interpolator* plugin = (Interpolator*)instance;
+
+	/* Control Input (float value) */
+	const float input = *(plugin->input);
+
+	/* Interpolated Output (pointer to float value) */
+	float* output = plugin->output;
+
+	/* We use two previous values and the input as the 'next' one */
+	float p1 = plugin->p1;
+	float p0 = plugin->p0;
+
+	const float inv_scount = 1.0f / (float)sample_count;
+
+	for (uint32_t s = 0; s < sample_count; ++s) {
+		const float interval = (float)s * inv_scount;
+
+		output[s] = interpolate(interval, p1, p0, input);
+	}
+
+	plugin->p1 = p0;
+	plugin->p0 = input;
+}
+
+static const LV2_Descriptor descriptor = {
+	"http://drobilla.net/plugins/blop/interpolator",
+	instantiate,
+	connect_port,
+	activate,
+	run,
+	NULL,
+	cleanup,
+	NULL,
+};
+
+LV2_SYMBOL_EXPORT const LV2_Descriptor*
+lv2_descriptor(uint32_t index)
+{
+	switch (index) {
+	case 0:  return &descriptor;
+	default: return NULL;
+	}
+}