1 files changed, 676 insertions, 0 deletions

diff --git a/plugins/eg-scope.lv2/examploscope_ui.c b/plugins/eg-scope.lv2/examploscope_ui.c
new file mode 100644
index 0000000..ce0000c
--- /dev/null
+++ b/plugins/eg-scope.lv2/examploscope_ui.c
@@ -0,0 +1,676 @@
+/*
+  Copyright 2013 Robin Gareus <robin@gareus.org>
+
+  Permission to use, copy, modify, and/or distribute this software for any
+  purpose with or without fee is hereby granted, provided that the above
+  copyright notice and this permission notice appear in all copies.
+
+  THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+
+#include "./uris.h"
+
+#include "lv2/atom/atom.h"
+#include "lv2/atom/forge.h"
+#include "lv2/atom/util.h"
+#include "lv2/core/lv2.h"
+#include "lv2/ui/ui.h"
+#include "lv2/urid/urid.h"
+
+#include <cairo.h>
+#include <gdk/gdk.h>
+#include <glib-object.h>
+#include <glib.h>
+#include <gobject/gclosure.h>
+#include <gtk/gtk.h>
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// Drawing area size
+#define DAWIDTH  (640)
+#define DAHEIGHT (200)
+
+/**
+   Max continuous points on path.  Many short-path segments are
+   expensive|inefficient long paths are not supported by all surfaces (usually
+   its a miter - not point - limit, depending on used cairo backend)
+*/
+#define MAX_CAIRO_PATH (128)
+
+/**
+   Representation of the raw audio-data for display (min | max) values for a
+   given 'index' position.
+*/
+typedef struct {
+	float data_min[DAWIDTH];
+	float data_max[DAWIDTH];
+
+	uint32_t idx;
+	uint32_t sub;
+} ScoChan;
+
+typedef struct {
+	LV2_Atom_Forge forge;
+	LV2_URID_Map*  map;
+	ScoLV2URIs     uris;
+
+	LV2UI_Write_Function write;
+	LV2UI_Controller     controller;
+
+	GtkWidget*     hbox;
+	GtkWidget*     vbox;
+	GtkWidget*     sep[2];
+	GtkWidget*     darea;
+	GtkWidget*     btn_pause;
+	GtkWidget*     lbl_speed;
+	GtkWidget*     lbl_amp;
+	GtkWidget*     spb_speed;
+	GtkWidget*     spb_amp;
+	GtkAdjustment* spb_speed_adj;
+	GtkAdjustment* spb_amp_adj;
+
+	ScoChan  chn[2];
+	uint32_t stride;
+	uint32_t n_channels;
+	bool     paused;
+	float    rate;
+	bool     updating;
+} EgScopeUI;
+
+
+/** Send current UI settings to backend. */
+static void
+send_ui_state(LV2UI_Handle handle)
+{
+	EgScopeUI*  ui   = (EgScopeUI*)handle;
+	const float gain = gtk_spin_button_get_value(GTK_SPIN_BUTTON(ui->spb_amp));
+
+	// Use local buffer on the stack to build atom
+	uint8_t obj_buf[1024];
+	lv2_atom_forge_set_buffer(&ui->forge, obj_buf, sizeof(obj_buf));
+
+	// Start a ui:State object
+	LV2_Atom_Forge_Frame frame;
+	LV2_Atom*            msg = (LV2_Atom*)lv2_atom_forge_object(
+		&ui->forge, &frame, 0, ui->uris.ui_State);
+
+	// msg[samples-per-pixel] = integer
+	lv2_atom_forge_key(&ui->forge, ui->uris.ui_spp);
+	lv2_atom_forge_int(&ui->forge, ui->stride);
+
+	// msg[amplitude] = float
+	lv2_atom_forge_key(&ui->forge, ui->uris.ui_amp);
+	lv2_atom_forge_float(&ui->forge, gain);
+
+	// Finish ui:State object
+	lv2_atom_forge_pop(&ui->forge, &frame);
+
+	// Send message to plugin port '0'
+	ui->write(ui->controller,
+	          0,
+	          lv2_atom_total_size(msg),
+	          ui->uris.atom_eventTransfer,
+	          msg);
+}
+
+/** Notify backend that UI is closed. */
+static void
+send_ui_disable(LV2UI_Handle handle)
+{
+	EgScopeUI* ui = (EgScopeUI*)handle;
+	send_ui_state(handle);
+
+	uint8_t obj_buf[64];
+	lv2_atom_forge_set_buffer(&ui->forge, obj_buf, sizeof(obj_buf));
+
+	LV2_Atom_Forge_Frame frame;
+	LV2_Atom*            msg = (LV2_Atom*)lv2_atom_forge_object(
+		&ui->forge, &frame, 0, ui->uris.ui_Off);
+	lv2_atom_forge_pop(&ui->forge, &frame);
+	ui->write(ui->controller,
+	          0,
+	          lv2_atom_total_size(msg),
+	          ui->uris.atom_eventTransfer,
+	          msg);
+}
+
+/**
+   Notify backend that UI is active.
+
+   The plugin should send state and enable data transmission.
+*/
+static void
+send_ui_enable(LV2UI_Handle handle)
+{
+	EgScopeUI* ui = (EgScopeUI*)handle;
+
+	uint8_t obj_buf[64];
+	lv2_atom_forge_set_buffer(&ui->forge, obj_buf, sizeof(obj_buf));
+
+	LV2_Atom_Forge_Frame frame;
+	LV2_Atom*            msg = (LV2_Atom*)lv2_atom_forge_object(
+		&ui->forge, &frame, 0, ui->uris.ui_On);
+	lv2_atom_forge_pop(&ui->forge, &frame);
+	ui->write(ui->controller,
+	          0,
+	          lv2_atom_total_size(msg),
+	          ui->uris.atom_eventTransfer,
+	          msg);
+}
+
+/** Gtk widget callback. */
+static gboolean
+on_cfg_changed(GtkWidget* widget, gpointer data)
+{
+	EgScopeUI* ui = (EgScopeUI*)data;
+	if (!ui->updating) {
+		// Only send UI state if the change is from user interaction
+		send_ui_state(data);
+	}
+	return TRUE;
+}
+
+/**
+   Gdk drawing area draw callback.
+
+   Called in Gtk's main thread and uses Cairo to draw the data.
+*/
+static gboolean
+on_expose_event(GtkWidget* widget, GdkEventExpose* ev, gpointer data)
+{
+	EgScopeUI*  ui   = (EgScopeUI*)data;
+	const float gain = gtk_spin_button_get_value(GTK_SPIN_BUTTON(ui->spb_amp));
+
+	// Get cairo type for the gtk window
+	cairo_t* cr;
+	cr = gdk_cairo_create(ui->darea->window);
+
+	// Limit cairo-drawing to exposed area
+	cairo_rectangle(cr, ev->area.x, ev->area.y, ev->area.width, ev->area.height);
+	cairo_clip(cr);
+
+	// Clear background
+	cairo_set_source_rgba(cr, 0.0, 0.0, 0.0, 1.0);
+	cairo_rectangle(cr, 0, 0, DAWIDTH, DAHEIGHT * ui->n_channels);
+	cairo_fill(cr);
+
+	cairo_set_line_width(cr, 1.0);
+
+	const uint32_t start = ev->area.x;
+	const uint32_t end   = ev->area.x + ev->area.width;
+
+	assert(start < DAWIDTH);
+	assert(end <= DAWIDTH);
+	assert(start < end);
+
+	for (uint32_t c = 0; c < ui->n_channels; ++c) {
+		ScoChan* chn = &ui->chn[c];
+
+		/* Drawing area Y-position of given sample-value.
+		 * Note: cairo-pixel at 0 spans -0.5 .. +0.5, hence (DAHEIGHT / 2.0 -0.5)
+		 * also the cairo Y-axis points upwards (hence 'minus value')
+		 *
+		 * == (   DAHEIGHT * (CHN)        // channel offset
+		 *      + (DAHEIGHT / 2) - 0.5    // vertical center -- '0'
+		 *      - (DAHEIGHT / 2) * (VAL) * (GAIN)
+		 *    )
+		 */
+		const float chn_y_offset = DAHEIGHT * c + DAHEIGHT * 0.5f - 0.5f;
+		const float chn_y_scale  = DAHEIGHT * 0.5f * gain;
+
+#define CYPOS(VAL) (chn_y_offset - (VAL) * chn_y_scale)
+
+		cairo_save(cr);
+
+		/* Restrict drawing to current channel area, don't bleed drawing into
+		   neighboring channels. */
+		cairo_rectangle(cr, 0, DAHEIGHT * c, DAWIDTH, DAHEIGHT);
+		cairo_clip(cr);
+
+		// Set color of wave-form
+		cairo_set_source_rgba(cr, 0.0, 1.0, 0.0, 1.0);
+
+		/* This is a somewhat 'smart' mechanism to plot audio data using
+		   alternating up/down line-directions.  It works well for both cases:
+		   1 pixel <= 1 sample and 1 pixel represents more than 1 sample, but
+		   is not ideal for either. */
+		if (start == chn->idx) {
+			cairo_move_to(cr, start - 0.5, CYPOS(0));
+		} else {
+			cairo_move_to(cr, start - 0.5, CYPOS(chn->data_max[start]));
+		}
+
+		uint32_t pathlength = 0;
+		for (uint32_t i = start; i < end; ++i) {
+			if (i == chn->idx) {
+				continue;
+			} else if (i % 2) {
+				cairo_line_to(cr, i - .5, CYPOS(chn->data_min[i]));
+				cairo_line_to(cr, i - .5, CYPOS(chn->data_max[i]));
+				++pathlength;
+			} else {
+				cairo_line_to(cr, i - .5, CYPOS(chn->data_max[i]));
+				cairo_line_to(cr, i - .5, CYPOS(chn->data_min[i]));
+				++pathlength;
+			}
+
+			/** Limit the max cairo path length.  This is an optimization trade
+			    off: too short path: high load CPU/GPU load.  too-long path:
+			    bad anti-aliasing, or possibly lost points */
+			if (pathlength > MAX_CAIRO_PATH) {
+				pathlength = 0;
+				cairo_stroke(cr);
+				if (i % 2) {
+					cairo_move_to(cr, i - .5, CYPOS(chn->data_max[i]));
+				} else {
+					cairo_move_to(cr, i - .5, CYPOS(chn->data_min[i]));
+				}
+			}
+		}
+
+		if (pathlength > 0) {
+			cairo_stroke(cr);
+		}
+
+		// Draw current position vertical line if display is slow
+		if (ui->stride >= ui->rate / 4800.0f || ui->paused) {
+			cairo_set_source_rgba(cr, .9, .2, .2, .6);
+			cairo_move_to(cr, chn->idx - .5, DAHEIGHT * c);
+			cairo_line_to(cr, chn->idx - .5, DAHEIGHT * (c + 1));
+			cairo_stroke(cr);
+		}
+
+		// Undo the 'clipping' restriction
+		cairo_restore(cr);
+
+		// Channel separator
+		if (c > 0) {
+			cairo_set_source_rgba(cr, .5, .5, .5, 1.0);
+			cairo_move_to(cr, 0, DAHEIGHT * c - .5);
+			cairo_line_to(cr, DAWIDTH, DAHEIGHT * c - .5);
+			cairo_stroke(cr);
+		}
+
+		// Zero scale line
+		cairo_set_source_rgba(cr, .3, .3, .7, .5);
+		cairo_move_to(cr, 0, DAHEIGHT * (c + .5) - .5);
+		cairo_line_to(cr, DAWIDTH, DAHEIGHT * (c + .5) - .5);
+		cairo_stroke(cr);
+	}
+
+	cairo_destroy(cr);
+	return TRUE;
+}
+
+/**
+   Parse raw audio data and prepare for later drawing.
+
+   Note this is a toy example, which is really a waveform display, not an
+   oscilloscope.  A serious scope would not display samples as is.
+
+   Signals above ~ 1/10 of the sampling-rate will not yield a useful visual
+   display and result in a rather unintuitive representation of the actual
+   waveform.
+
+   Ideally the audio-data would be buffered and upsampled here and after that
+   written in a display buffer for later use.
+
+   For more information, see
+   https://wiki.xiph.org/Videos/Digital_Show_and_Tell
+   http://lac.linuxaudio.org/2013/papers/36.pdf
+   and https://github.com/x42/sisco.lv2
+*/
+static int
+process_channel(EgScopeUI*   ui,
+                ScoChan*     chn,
+                const size_t n_elem,
+                float const* data,
+                uint32_t*    idx_start,
+                uint32_t*    idx_end)
+{
+	int overflow = 0;
+	*idx_start = chn->idx;
+	for (size_t i = 0; i < n_elem; ++i) {
+		if (data[i] < chn->data_min[chn->idx]) {
+			chn->data_min[chn->idx] = data[i];
+		}
+		if (data[i] > chn->data_max[chn->idx]) {
+			chn->data_max[chn->idx] = data[i];
+		}
+		if (++chn->sub >= ui->stride) {
+			chn->sub = 0;
+			chn->idx = (chn->idx + 1) % DAWIDTH;
+			if (chn->idx == 0) {
+				++overflow;
+			}
+			chn->data_min[chn->idx] = 1.0;
+			chn->data_max[chn->idx] = -1.0;
+		}
+	}
+	*idx_end = chn->idx;
+	return overflow;
+}
+
+/**
+   Called via port_event() which is called by the host, typically at a rate of
+   around 25 FPS.
+*/
+static void
+update_scope(EgScopeUI*    ui,
+             const int32_t channel,
+             const size_t  n_elem,
+             float const*  data)
+{
+	// Never trust input data which could lead to application failure.
+	if (channel < 0 || (uint32_t)channel > ui->n_channels) {
+		return;
+	}
+
+	// Update state in sync with 1st channel
+	if (channel == 0) {
+		ui->stride = gtk_spin_button_get_value(GTK_SPIN_BUTTON(ui->spb_speed));
+		const bool paused = gtk_toggle_button_get_active(
+			GTK_TOGGLE_BUTTON(ui->btn_pause));
+
+		if (paused != ui->paused) {
+			ui->paused = paused;
+			gtk_widget_queue_draw(ui->darea);
+		}
+	}
+	if (ui->paused) {
+		return;
+	}
+
+	uint32_t idx_start;  // Display pixel start
+	uint32_t idx_end;    // Display pixel end
+	int      overflow;   // Received more audio-data than display-pixel
+
+	// Process this channel's audio-data for display
+	ScoChan* chn = &ui->chn[channel];
+	overflow = process_channel(ui, chn, n_elem, data, &idx_start, &idx_end);
+
+	// Signal gtk's main thread to redraw the widget after the last channel
+	if ((uint32_t)channel + 1 == ui->n_channels) {
+		if (overflow > 1) {
+			// Redraw complete widget
+			gtk_widget_queue_draw(ui->darea);
+		} else if (idx_end > idx_start) {
+			// Redraw area between start -> end pixel
+			gtk_widget_queue_draw_area(ui->darea, idx_start - 2, 0, 3
+			                           + idx_end - idx_start,
+			                           DAHEIGHT * ui->n_channels);
+		} else if (idx_end < idx_start) {
+			// Wrap-around: redraw area between 0->start AND end->right-end
+			gtk_widget_queue_draw_area(
+				ui->darea,
+				idx_start - 2, 0,
+				3 + DAWIDTH - idx_start, DAHEIGHT * ui->n_channels);
+			gtk_widget_queue_draw_area(
+				ui->darea,
+				0, 0,
+				idx_end + 1, DAHEIGHT * ui->n_channels);
+		}
+	}
+}
+
+static LV2UI_Handle
+instantiate(const LV2UI_Descriptor*   descriptor,
+            const char*               plugin_uri,
+            const char*               bundle_path,
+            LV2UI_Write_Function      write_function,
+            LV2UI_Controller          controller,
+            LV2UI_Widget*             widget,
+            const LV2_Feature* const* features)
+{
+	EgScopeUI* ui = (EgScopeUI*)calloc(1, sizeof(EgScopeUI));
+
+	if (!ui) {
+		fprintf(stderr, "EgScope.lv2 UI: out of memory\n");
+		return NULL;
+	}
+
+	ui->map = NULL;
+	*widget = NULL;
+
+	if (!strcmp(plugin_uri, SCO_URI "#Mono")) {
+		ui->n_channels = 1;
+	} else if (!strcmp(plugin_uri, SCO_URI "#Stereo")) {
+		ui->n_channels = 2;
+	} else {
+		free(ui);
+		return NULL;
+	}
+
+	for (int i = 0; features[i]; ++i) {
+		if (!strcmp(features[i]->URI, LV2_URID_URI "#map")) {
+			ui->map = (LV2_URID_Map*)features[i]->data;
+		}
+	}
+
+	if (!ui->map) {
+		fprintf(stderr, "EgScope.lv2 UI: Host does not support urid:map\n");
+		free(ui);
+		return NULL;
+	}
+
+	// Initialize private data structure
+	ui->write      = write_function;
+	ui->controller = controller;
+
+	ui->vbox   = NULL;
+	ui->hbox   = NULL;
+	ui->darea  = NULL;
+	ui->stride = 25;
+	ui->paused = false;
+	ui->rate   = 48000;
+
+	ui->chn[0].idx = 0;
+	ui->chn[0].sub = 0;
+	ui->chn[1].idx = 0;
+	ui->chn[1].sub = 0;
+	memset(ui->chn[0].data_min, 0, sizeof(float) * DAWIDTH);
+	memset(ui->chn[0].data_max, 0, sizeof(float) * DAWIDTH);
+	memset(ui->chn[1].data_min, 0, sizeof(float) * DAWIDTH);
+	memset(ui->chn[1].data_max, 0, sizeof(float) * DAWIDTH);
+
+	map_sco_uris(ui->map, &ui->uris);
+	lv2_atom_forge_init(&ui->forge, ui->map);
+
+	// Setup UI
+	ui->hbox = gtk_hbox_new(FALSE, 0);
+	ui->vbox = gtk_vbox_new(FALSE, 0);
+
+	ui->darea = gtk_drawing_area_new();
+	gtk_widget_set_size_request(ui->darea, DAWIDTH, DAHEIGHT * ui->n_channels);
+
+	ui->lbl_speed = gtk_label_new("Samples/Pixel");
+	ui->lbl_amp   = gtk_label_new("Amplitude");
+
+	ui->sep[0]    = gtk_hseparator_new();
+	ui->sep[1]    = gtk_label_new("");
+	ui->btn_pause = gtk_toggle_button_new_with_label("Pause");
+
+	ui->spb_speed_adj = (GtkAdjustment*)gtk_adjustment_new(
+			25.0, 1.0, 1000.0, 1.0, 5.0, 0.0);
+	ui->spb_speed = gtk_spin_button_new(ui->spb_speed_adj, 1.0, 0);
+
+	ui->spb_amp_adj = (GtkAdjustment*)gtk_adjustment_new(
+		1.0, 0.1, 6.0, 0.1, 1.0, 0.0);
+	ui->spb_amp = gtk_spin_button_new(ui->spb_amp_adj, 0.1, 1);
+
+	gtk_box_pack_start(GTK_BOX(ui->hbox), ui->darea,     FALSE, FALSE, 0);
+	gtk_box_pack_start(GTK_BOX(ui->hbox), ui->vbox,      FALSE, FALSE, 4);
+
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->lbl_speed, FALSE, FALSE, 2);
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->spb_speed, FALSE, FALSE, 2);
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->sep[0],    FALSE, FALSE, 8);
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->lbl_amp,   FALSE, FALSE, 2);
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->spb_amp,   FALSE, FALSE, 2);
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->sep[1],     TRUE, FALSE, 8);
+	gtk_box_pack_start(GTK_BOX(ui->vbox), ui->btn_pause, FALSE, FALSE, 2);
+
+	g_signal_connect(G_OBJECT(ui->darea), "expose_event",
+	                 G_CALLBACK(on_expose_event), ui);
+	g_signal_connect(G_OBJECT(ui->spb_amp), "value-changed",
+	                 G_CALLBACK(on_cfg_changed), ui);
+	g_signal_connect(G_OBJECT(ui->spb_speed), "value-changed",
+	                 G_CALLBACK(on_cfg_changed), ui);
+
+	*widget = ui->hbox;
+
+	/* Send UIOn message to plugin, which will request state and enable message
+	   transmission. */
+	send_ui_enable(ui);
+
+	return ui;
+}
+
+static void
+cleanup(LV2UI_Handle handle)
+{
+	EgScopeUI* ui = (EgScopeUI*)handle;
+	/* Send UIOff message to plugin, which will save state and disable message
+	 * transmission. */
+	send_ui_disable(ui);
+	gtk_widget_destroy(ui->darea);
+	free(ui);
+}
+
+static int
+recv_raw_audio(EgScopeUI* ui, const LV2_Atom_Object* obj)
+{
+	const LV2_Atom* chan_val = NULL;
+	const LV2_Atom* data_val = NULL;
+	const int n_props  = lv2_atom_object_get(
+		obj,
+		ui->uris.channelID, &chan_val,
+		ui->uris.audioData, &data_val,
+		NULL);
+
+	if (n_props != 2 ||
+	    chan_val->type != ui->uris.atom_Int ||
+	    data_val->type != ui->uris.atom_Vector) {
+		// Object does not have the required properties with correct types
+		fprintf(stderr, "eg-scope.lv2 UI error: Corrupt audio message\n");
+		return 1;
+	}
+
+	// Get the values we need from the body of the property value atoms
+	const int32_t          chn = ((const LV2_Atom_Int*)chan_val)->body;
+	const LV2_Atom_Vector* vec = (const LV2_Atom_Vector*)data_val;
+	if (vec->body.child_type != ui->uris.atom_Float) {
+		return 1;  // Vector has incorrect element type
+	}
+
+	// Number of elements = (total size - header size) / element size
+	const size_t n_elem = ((data_val->size - sizeof(LV2_Atom_Vector_Body))
+	                       / sizeof(float));
+
+	// Float elements immediately follow the vector body header
+	const float* data = (const float*)(&vec->body + 1);
+
+	// Update display
+	update_scope(ui, chn, n_elem, data);
+	return 0;
+}
+
+static int
+recv_ui_state(EgScopeUI* ui, const LV2_Atom_Object* obj)
+{
+	const LV2_Atom* spp_val  = NULL;
+	const LV2_Atom* amp_val  = NULL;
+	const LV2_Atom* rate_val = NULL;
+	const int n_props  = lv2_atom_object_get(
+		obj,
+		ui->uris.ui_spp, &spp_val,
+		ui->uris.ui_amp, &amp_val,
+		ui->uris.param_sampleRate, &rate_val,
+		NULL);
+
+	if (n_props != 3 ||
+		spp_val->type != ui->uris.atom_Int ||
+		amp_val->type != ui->uris.atom_Float ||
+	    rate_val->type != ui->uris.atom_Float) {
+		// Object does not have the required properties with correct types
+		fprintf(stderr, "eg-scope.lv2 UI error: Corrupt state message\n");
+		return 1;
+	}
+
+	// Get the values we need from the body of the property value atoms
+	const int32_t spp  = ((const LV2_Atom_Int*)spp_val)->body;
+	const float   amp  = ((const LV2_Atom_Float*)amp_val)->body;
+	const float   rate = ((const LV2_Atom_Float*)rate_val)->body;
+
+	// Disable transmission and update UI
+	ui->updating = true;
+	gtk_spin_button_set_value(GTK_SPIN_BUTTON(ui->spb_speed), spp);
+	gtk_spin_button_set_value(GTK_SPIN_BUTTON(ui->spb_amp),   amp);
+	ui->updating = false;
+	ui->rate = rate;
+
+	return 0;
+}
+
+/**
+   Receive data from the DSP-backend.
+
+   This is called by the host, typically at a rate of around 25 FPS.
+
+   Ideally this happens regularly and with relatively low latency, but there
+   are no hard guarantees about message delivery.
+*/
+static void
+port_event(LV2UI_Handle handle,
+           uint32_t     port_index,
+           uint32_t     buffer_size,
+           uint32_t     format,
+           const void*  buffer)
+{
+	EgScopeUI*      ui   = (EgScopeUI*)handle;
+	const LV2_Atom* atom = (const LV2_Atom*)buffer;
+
+	/* Check type of data received
+	 *  - format == 0: Control port event (float)
+	 *  - format > 0:  Message (atom)
+	 */
+	if (format == ui->uris.atom_eventTransfer &&
+	    lv2_atom_forge_is_object_type(&ui->forge, atom->type)) {
+		const LV2_Atom_Object* obj = (const LV2_Atom_Object*)atom;
+		if (obj->body.otype == ui->uris.RawAudio) {
+			recv_raw_audio(ui, obj);
+		} else if (obj->body.otype == ui->uris.ui_State) {
+			recv_ui_state(ui, obj);
+		}
+	}
+}
+
+static const LV2UI_Descriptor descriptor = {
+	SCO_URI "#ui",
+	instantiate,
+	cleanup,
+	port_event,
+	NULL
+};
+
+LV2_SYMBOL_EXPORT
+const LV2UI_Descriptor*
+lv2ui_descriptor(uint32_t index)
+{
+	switch (index) {
+	case 0:
+		return &descriptor;
+	default:
+		return NULL;
+	}
+}