eg-sampler: Add waveform display to UI

6 files changed, 466 insertions, 76 deletions

diff --git a/plugins/eg-sampler.lv2/README.txt b/plugins/eg-sampler.lv2/README.txt
index 4eed9e6..8d136fa 100644
--- a/plugins/eg-sampler.lv2/README.txt
+++ b/plugins/eg-sampler.lv2/README.txt
@@ -11,3 +11,4 @@ This plugin illustrates:
 - Use of the log extension to print log messages via the host
 - Saving plugin state via the state extension
 - Dynamic plugin control via the same properties saved to state
+- Network-transparent waveform display with incremental peak transmission
diff --git a/plugins/eg-sampler.lv2/peaks.h b/plugins/eg-sampler.lv2/peaks.h
new file mode 100644
index 0000000..69688b8
--- /dev/null
+++ b/plugins/eg-sampler.lv2/peaks.h
@@ -0,0 +1,270 @@
+/*
+  LV2 audio peaks utilities
+  Copyright 2016 David Robillard <d@drobilla.net>
+
+  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.
+*/
+
+/**
+   This file defines utilities for sending and receiving audio peaks for
+   waveform display.  The functionality is divided into two objects:
+   PeaksSender, for sending peaks updates from the plugin, and PeaksReceiver,
+   for receiving such updates and caching the peaks.
+
+   This allows peaks for a waveform of any size at any resolution to be
+   requested, with reasonably sized incremental updates sent over plugin ports.
+*/
+
+#ifndef PEAKS_H_INCLUDED
+#define PEAKS_H_INCLUDED
+
+#include <math.h>
+
+#include "lv2/lv2plug.in/ns/ext/atom/forge.h"
+
+#define PEAKS_URI          "http://lv2plug.in/ns/peaks#"
+#define PEAKS__PeakUpdate  PEAKS_URI "PeakUpdate"
+#define PEAKS__magnitudes  PEAKS_URI "magnitudes"
+#define PEAKS__offset      PEAKS_URI "offset"
+#define PEAKS__total       PEAKS_URI "total"
+
+#ifndef MIN
+#    define MIN(a, b) (((a) < (b)) ? (a) : (b))
+#endif
+#ifndef MAX
+#    define MAX(a, b) (((a) > (b)) ? (a) : (b))
+#endif
+
+typedef struct {
+	LV2_URID atom_Float;
+	LV2_URID atom_Int;
+	LV2_URID atom_Vector;
+	LV2_URID peaks_PeakUpdate;
+	LV2_URID peaks_magnitudes;
+	LV2_URID peaks_offset;
+	LV2_URID peaks_total;
+} PeaksURIs;
+
+typedef struct {
+	PeaksURIs    uris;            ///< URIDs used in protocol
+	const float* samples;         ///< Sample data
+	uint32_t     n_samples;       ///< Total number of samples
+	uint32_t     n_peaks;         ///< Total number of peaks
+	uint32_t     current_offset;  ///< Current peak offset
+	bool         sending;         ///< True iff currently sending
+} PeaksSender;
+
+typedef struct {
+	PeaksURIs uris;     ///< URIDs used in protocol
+	float*    peaks;    ///< Received peaks, or zeroes
+	uint32_t  n_peaks;  ///< Total number of peaks
+} PeaksReceiver;
+
+/**
+   Map URIs used in the peaks protocol.
+*/
+static inline void
+peaks_map_uris(PeaksURIs* uris, LV2_URID_Map* map)
+{
+	uris->atom_Float       = map->map(map->handle, LV2_ATOM__Float);
+	uris->atom_Int         = map->map(map->handle, LV2_ATOM__Int);
+	uris->atom_Vector      = map->map(map->handle, LV2_ATOM__Vector);
+	uris->peaks_PeakUpdate = map->map(map->handle, PEAKS__PeakUpdate);
+	uris->peaks_magnitudes = map->map(map->handle, PEAKS__magnitudes);
+	uris->peaks_offset     = map->map(map->handle, PEAKS__offset);
+	uris->peaks_total      = map->map(map->handle, PEAKS__total);
+}
+
+/**
+   Initialise peaks sender.  The new sender is inactive and will do nothing
+   when `peaks_sender_send()` is called, until a transmission is started with
+   `peaks_sender_start()`.
+*/
+static inline PeaksSender*
+peaks_sender_init(PeaksSender* sender, LV2_URID_Map* map)
+{
+	memset(sender, 0, sizeof(*sender));
+	peaks_map_uris(&sender->uris, map);
+	return sender;
+}
+
+/**
+   Prepare to start a new peaks transmission.  After this is called, the peaks
+   can be sent with successive calls to `peaks_sender_send()`.
+*/
+static inline void
+peaks_sender_start(PeaksSender* sender,
+                   const float* samples,
+                   uint32_t     n_samples,
+                   uint32_t     n_peaks)
+{
+	sender->samples        = samples;
+	sender->n_samples      = n_samples;
+	sender->n_peaks        = n_peaks;
+	sender->current_offset = 0;
+	sender->sending        = true;
+}
+
+/**
+   Forge a message which sends a range of peaks.  Writes a peaks:PeakUpdate
+   object to `forge`, like:
+
+   [source,n3]
+   ----
+   []
+   	   a peaks:PeakUpdate ;
+   	   peaks:offset 256 ;
+   	   peaks:total 1024 ;
+   	   peaks:magnitudes [ 0.2f, 0.3f, ... ] .
+   ----
+*/
+static inline bool
+peaks_sender_send(PeaksSender*    sender,
+                  LV2_Atom_Forge* forge,
+                  uint32_t        n_frames,
+                  uint32_t        offset)
+{
+	const PeaksURIs* uris = &sender->uris;
+	if (!sender->sending || sender->current_offset >= sender->n_peaks) {
+		return sender->sending = false;
+	}
+
+	// Start PeakUpdate object
+	lv2_atom_forge_frame_time(forge, offset);
+	LV2_Atom_Forge_Frame frame;
+	lv2_atom_forge_object(forge, &frame, 0, uris->peaks_PeakUpdate);
+
+	// eg:offset = OFFSET
+	lv2_atom_forge_key(forge, uris->peaks_offset);
+	lv2_atom_forge_int(forge, sender->current_offset);
+
+	// eg:total = TOTAL
+	lv2_atom_forge_key(forge, uris->peaks_total);
+	lv2_atom_forge_int(forge, sender->n_peaks);
+
+	// eg:magnitudes = Vector<Float>(PEAK, PEAK, ...)
+	lv2_atom_forge_key(forge, uris->peaks_magnitudes);
+	LV2_Atom_Forge_Frame vec_frame;
+	lv2_atom_forge_vector_head(
+		forge, &vec_frame, sizeof(float), uris->atom_Float);
+
+	// Calculate how many peaks to send this update
+	const int      chunk_size = MAX(1, sender->n_samples / sender->n_peaks);
+	const uint32_t space      = forge->size - forge->offset;
+	const uint32_t remaining  = sender->n_peaks - sender->current_offset;
+	const int      n_update   = MIN(remaining,
+	                                MIN(n_frames / 4, space / sizeof(float)));
+
+	// Calculate peak (maximum magnitude) for each chunk
+	for (int i = 0; i < n_update; ++i) {
+		const int start = (sender->current_offset + i) * chunk_size;
+		float     peak  = 0.0f;
+		for (int j = 0; j < chunk_size; ++j) {
+			peak = fmaxf(peak, fabsf(sender->samples[start + j]));
+		}
+		lv2_atom_forge_float(forge, peak);
+	}
+
+	// Finish message
+	lv2_atom_forge_pop(forge, &vec_frame);
+	lv2_atom_forge_pop(forge, &frame);
+
+	sender->current_offset += n_update;
+	return true;
+}
+
+/**
+   Initialise a peaks receiver.  The receiver stores an array of all peaks,
+   which is updated incrementally with peaks_receiver_receive().
+*/
+static inline PeaksReceiver*
+peaks_receiver_init(PeaksReceiver* receiver, LV2_URID_Map* map)
+{
+	memset(receiver, 0, sizeof(*receiver));
+	peaks_map_uris(&receiver->uris, map);
+	return receiver;
+}
+
+/**
+   Clear stored peaks and free all memory.  This should be called when the
+   peaks are to be updated with a different audio source.
+*/
+static inline void
+peaks_receiver_clear(PeaksReceiver* receiver)
+{
+	free(receiver->peaks);
+	receiver->peaks   = NULL;
+	receiver->n_peaks = 0;
+}
+
+/**
+   Handle PeakUpdate message.
+
+   The stored peaks array is updated with the slice of peaks in `update`,
+   resizing if necessary while preserving contents.
+
+   Returns 0 if peaks have been updated, negative on error.
+*/
+static inline int
+peaks_receiver_receive(PeaksReceiver* receiver, const LV2_Atom_Object* update)
+{
+	const PeaksURIs* uris = &receiver->uris;
+
+	// Get properties of interest from update
+	const LV2_Atom_Int*    offset = NULL;
+	const LV2_Atom_Int*    total  = NULL;
+	const LV2_Atom_Vector* peaks  = NULL;
+	lv2_atom_object_get_typed(update,
+	                          uris->peaks_offset,     &offset, uris->atom_Int,
+	                          uris->peaks_total,      &total,  uris->atom_Int,
+	                          uris->peaks_magnitudes, &peaks,  uris->atom_Vector,
+	                          0);
+
+	if (!offset || !total || !peaks ||
+	    peaks->body.child_type != uris->atom_Float) {
+		return -1;  // Invalid update
+	}
+
+	const uint32_t n = (uint32_t)total->body;
+	if (receiver->n_peaks != n) {
+		// Update is for a different total number of peaks, resize
+		receiver->peaks = (float*)realloc(receiver->peaks, n * sizeof(float));
+		if (receiver->n_peaks > 0 && receiver->n_peaks < n) {
+			/* The peaks array is being expanded.  Copy the old peaks,
+			   duplicating each as necessary to fill the new peaks buffer.
+			   This preserves the current peaks so that the peaks array can be
+			   reasonably drawn at any time, but the resolution will increase
+			   as new updates arrive. */
+			const int n_per = n / receiver->n_peaks;
+			for (int i = n - 1; i >= 0; --i) {
+				receiver->peaks[i] = receiver->peaks[i / n_per];
+			}
+		} else if (receiver->n_peaks > 0) {
+			/* The peak array is being shrunk.  Similar to the above. */
+			const int n_per = receiver->n_peaks / n;
+			for (int i = n - 1; i >= 0; --i) {
+				receiver->peaks[i] = receiver->peaks[i * n_per];
+			}
+		}
+		receiver->n_peaks = n;
+	}
+
+	// Copy vector contents to corresponding range in peaks array
+	memcpy(receiver->peaks + offset->body,
+	       peaks + 1,
+	       peaks->atom.size - sizeof(LV2_Atom_Vector_Body));
+
+	return 0;
+}
+
+#endif // PEAKS_H_INCLUDED
diff --git a/plugins/eg-sampler.lv2/sampler.c b/plugins/eg-sampler.lv2/sampler.c
index 36acb2f..627ba45 100644
--- a/plugins/eg-sampler.lv2/sampler.c
+++ b/plugins/eg-sampler.lv2/sampler.c
@@ -38,8 +38,9 @@
 #include "lv2/lv2plug.in/ns/lv2core/lv2.h"
 #include "lv2/lv2plug.in/ns/lv2core/lv2_util.h"
 
-#include "uris.h"
 #include "atom_sink.h"
+#include "peaks.h"
+#include "uris.h"
 
 enum {
 	SAMPLER_CONTROL = 0,
@@ -60,16 +61,15 @@ typedef struct {
 	LV2_Worker_Schedule* schedule;
 	LV2_Log_Logger       logger;
 
-	// Forge for creating atoms
-	LV2_Atom_Forge forge;
-
 	// Ports
 	const LV2_Atom_Sequence* control_port;
 	LV2_Atom_Sequence*       notify_port;
 	float*                   output_port;
 
-	// Forge frame for notify port (for writing worker replies)
-	LV2_Atom_Forge_Frame notify_frame;
+	// Communication utilities
+	LV2_Atom_Forge_Frame notify_frame;  ///< Cached for worker replies
+	LV2_Atom_Forge       forge;         ///< Forge for writing atoms in run thread
+	PeaksSender          psend;         ///< Audio peaks sender
 
 	// URIs
 	SamplerURIs uris;
@@ -113,19 +113,25 @@ load_sample(LV2_Log_Logger* logger, const char* path)
 	Sample* const  sample   = (Sample*)malloc(sizeof(Sample));
 	SF_INFO* const info     = &sample->info;
 	SNDFILE* const sndfile  = sf_open(path, SFM_READ, info);
+	float*         data     = NULL;
+	bool           error    = true;
+	if (!sndfile || !info->frames) {
+		lv2_log_error(logger, "Failed to open %s\n", path);
+	} else if (info->channels != 1) {
+		lv2_log_error(logger, "%s has %d channels\n", path, info->channels);
+	} else if (!(data = (float*)malloc(sizeof(float) * info->frames))) {
+		lv2_log_error(logger, "Failed to allocate memory for sample\n");
+	} else {
+		error = false;
+	}
 
-	if (!sndfile || !info->frames || (info->channels != 1)) {
-		lv2_log_error(logger, "Failed to open sample '%s'\n", path);
+	if (error) {
 		free(sample);
+		free(data);
+		sf_close(sndfile);
 		return NULL;
 	}
 
-	// Read data
-	float* const data = (float*)malloc(sizeof(float) * info->frames);
-	if (!data) {
-		lv2_log_error(logger, "Failed to allocate memory for sample\n");
-		return NULL;
-	}
 	sf_seek(sndfile, 0ul, SEEK_SET);
 	sf_read_float(sndfile, data, info->frames);
 	sf_close(sndfile);
@@ -155,7 +161,7 @@ free_sample(Sampler* self, Sample* sample)
 
    This is called for every piece of work scheduled in the audio thread using
    self->schedule->schedule_work().  A reply can be sent back to the audio
-   thread using the provided respond function.
+   thread using the provided `respond` function.
 */
 static LV2_Worker_Status
 work(LV2_Handle                  instance,
@@ -275,6 +281,7 @@ instantiate(const LV2_Descriptor*     descriptor,
 	// Map URIs and initialise forge
 	map_sampler_uris(self->map, &self->uris);
 	lv2_atom_forge_init(&self->forge, self->map);
+	peaks_sender_init(&self->psend, self->map);
 
 	return (LV2_Handle)self;
 }
@@ -308,6 +315,7 @@ run(LV2_Handle instance,
 {
 	Sampler*     self        = (Sampler*)instance;
 	SamplerURIs* uris        = &self->uris;
+	PeaksURIs*   peaks_uris  = &self->psend.uris;
 	sf_count_t   start_frame = 0;
 	sf_count_t   pos         = 0;
 	float*       output      = self->output_port;
@@ -378,11 +386,25 @@ run(LV2_Handle instance,
 					}
 				}
 			} else if (obj->body.otype == uris->patch_Get) {
-				// Received a get message, emit our state (probably to UI)
-				lv2_atom_forge_frame_time(&self->forge, self->frame_offset);
-				write_set_file(&self->forge, &self->uris,
-				               self->sample->path,
-				               self->sample->path_len);
+				const LV2_Atom_URID* accept  = NULL;
+				const LV2_Atom_Int*  n_peaks = NULL;
+				lv2_atom_object_get_typed(
+					obj,
+					uris->patch_accept,      &accept,  uris->atom_URID,
+					peaks_uris->peaks_total, &n_peaks, peaks_uris->atom_Int, 0);
+				if (accept && accept->body == peaks_uris->peaks_PeakUpdate) {
+					// Received a request for peaks, prepare for transmission
+					peaks_sender_start(&self->psend,
+					                   self->sample->data,
+					                   self->sample->info.frames,
+					                   n_peaks->body);
+				} else {
+					// Received a get message, emit our state (probably to UI)
+					lv2_atom_forge_frame_time(&self->forge, self->frame_offset);
+					write_set_file(&self->forge, &self->uris,
+					               self->sample->path,
+					               self->sample->path_len);
+				}
 			} else {
 				lv2_log_trace(&self->logger,
 				              "Unknown object type %d\n", obj->body.otype);
@@ -393,6 +415,8 @@ run(LV2_Handle instance,
 		}
 	}
 
+	peaks_sender_send(&self->psend, &self->forge, sample_count, self->frame_offset);
+
 	// Render the sample (possibly already in progress)
 	if (self->play) {
 		uint32_t       f  = self->frame;
diff --git a/plugins/eg-sampler.lv2/sampler.ttl b/plugins/eg-sampler.lv2/sampler.ttl
index f4a9c43..c6103a3 100644
--- a/plugins/eg-sampler.lv2/sampler.ttl
+++ b/plugins/eg-sampler.lv2/sampler.ttl
@@ -16,7 +16,7 @@
 
 <http://lv2plug.in/plugins/eg-sampler>
 	a lv2:Plugin ;
-	doap:name "Example Sampler" ;
+	doap:name "Exampler" ;
 	doap:license <http://opensource.org/licenses/isc> ;
 	lv2:project <http://lv2plug.in/ns/lv2> ;
 	lv2:requiredFeature state:loadDefaultState ,
diff --git a/plugins/eg-sampler.lv2/sampler_ui.c b/plugins/eg-sampler.lv2/sampler_ui.c
index 23204c5..2373a4d 100644
--- a/plugins/eg-sampler.lv2/sampler_ui.c
+++ b/plugins/eg-sampler.lv2/sampler_ui.c
@@ -28,64 +28,136 @@
 #include "lv2/lv2plug.in/ns/extensions/ui/ui.h"
 #include "lv2/lv2plug.in/ns/lv2core/lv2_util.h"
 
-#include "./uris.h"
+#include "peaks.h"
+#include "uris.h"
 
 #define SAMPLER_UI_URI "http://lv2plug.in/plugins/eg-sampler#ui"
 
+#define MIN_CANVAS_W 128
+#define MIN_CANVAS_H 80
+
 typedef struct {
 	LV2_Atom_Forge forge;
 	LV2_URID_Map*  map;
 	LV2_Log_Logger logger;
 	SamplerURIs    uris;
+	PeaksReceiver  precv;
 
 	LV2UI_Write_Function write;
 	LV2UI_Controller     controller;
 
 	GtkWidget* box;
 	GtkWidget* button;
-	GtkWidget* label;
+	GtkWidget* canvas;
 	GtkWidget* window;  /* For optional show interface. */
+
+	uint32_t width;
+	uint32_t requested_n_peaks;
+	char*    filename;
+
+	uint8_t forge_buf[1024];
 } SamplerUI;
 
 static void
-on_load_clicked(GtkWidget* widget,
-                void*      handle)
+on_file_set(GtkFileChooserButton* widget, void* handle)
 {
 	SamplerUI* ui = (SamplerUI*)handle;
 
-	/* Create a dialog to select a sample file. */
-	GtkWidget* dialog = gtk_file_chooser_dialog_new(
-		"Load Sample",
-		NULL,
-		GTK_FILE_CHOOSER_ACTION_OPEN,
-		GTK_STOCK_CANCEL, GTK_RESPONSE_CANCEL,
-		GTK_STOCK_OPEN, GTK_RESPONSE_ACCEPT,
-		NULL);
+	// Get the filename from the file chooser
+	char* filename = gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(widget));
 
-	/* Run the dialog, and return if it is cancelled. */
-	if (gtk_dialog_run(GTK_DIALOG(dialog)) != GTK_RESPONSE_ACCEPT) {
-		gtk_widget_destroy(dialog);
-		return;
-	}
+	// Write a set message to the plugin to load new file
+	lv2_atom_forge_set_buffer(&ui->forge, ui->forge_buf, sizeof(ui->forge_buf));
+	LV2_Atom* msg = (LV2_Atom*)write_set_file(&ui->forge, &ui->uris,
+	                                          filename, strlen(filename));
 
-	/* Get the file path from the dialog. */
-	char* filename = gtk_file_chooser_get_filename(GTK_FILE_CHOOSER(dialog));
+	ui->write(ui->controller, 0, lv2_atom_total_size(msg),
+	          ui->uris.atom_eventTransfer,
+	          msg);
 
-	/* Got what we need, destroy the dialog. */
-	gtk_widget_destroy(dialog);
+	g_free(filename);
+}
 
-#define OBJ_BUF_SIZE 1024
-	uint8_t obj_buf[OBJ_BUF_SIZE];
-	lv2_atom_forge_set_buffer(&ui->forge, obj_buf, OBJ_BUF_SIZE);
+static void
+request_peaks(SamplerUI* ui, uint32_t n_peaks)
+{
+	lv2_atom_forge_set_buffer(&ui->forge, ui->forge_buf, sizeof(ui->forge_buf));
 
-	LV2_Atom* msg = (LV2_Atom*)write_set_file(&ui->forge, &ui->uris,
-	                                          filename, strlen(filename));
+	LV2_Atom_Forge_Frame frame;
+	lv2_atom_forge_object(&ui->forge, &frame, 0, ui->uris.patch_Get);
+	lv2_atom_forge_key(&ui->forge, ui->uris.patch_accept);
+	lv2_atom_forge_urid(&ui->forge, ui->precv.uris.peaks_PeakUpdate);
+	lv2_atom_forge_key(&ui->forge, ui->precv.uris.peaks_total);
+	lv2_atom_forge_int(&ui->forge, n_peaks);
+	lv2_atom_forge_pop(&ui->forge, &frame);
 
+	LV2_Atom* msg = lv2_atom_forge_deref(&ui->forge, frame.ref);
 	ui->write(ui->controller, 0, lv2_atom_total_size(msg),
 	          ui->uris.atom_eventTransfer,
 	          msg);
 
-	g_free(filename);
+	ui->requested_n_peaks = n_peaks;
+}
+
+/** Set Cairo color to a GDK color (to follow Gtk theme). */
+static void
+cairo_set_source_gdk(cairo_t* cr, const GdkColor* color)
+{
+	cairo_set_source_rgb(
+		cr, color->red / 65535.0, color->green / 65535.0, color->blue / 65535.0);
+
+}
+
+static gboolean
+on_canvas_expose(GtkWidget* widget, GdkEventExpose* event, gpointer data)
+{
+	SamplerUI* ui = (SamplerUI*)data;
+
+	GtkAllocation size;
+	gtk_widget_get_allocation(widget, &size);
+
+	ui->width = size.width;
+	if ((uint32_t)ui->width > 2 * ui->requested_n_peaks) {
+		request_peaks(ui, 2 * ui->requested_n_peaks);
+	}
+
+	cairo_t* cr = gdk_cairo_create(gtk_widget_get_window(widget));
+
+	const int mid_y = size.height / 2;
+
+	const float* const peaks   = ui->precv.peaks;
+	const int32_t      n_peaks = ui->precv.n_peaks;
+	if (peaks) {
+		// Draw waveform
+		const double scale = size.width / ((double)n_peaks - 1.0f);
+
+		// Start at left origin
+		cairo_move_to(cr, 0, mid_y);
+
+		// Draw line through top peaks
+		for (int i = 0; i < n_peaks; ++i) {
+			const float peak = peaks[i];
+			cairo_line_to(cr, i * scale, mid_y + (peak / 2.0f) * size.height);
+		}
+
+		// Continue through bottom peaks
+		for (int i = n_peaks - 1; i >= 0; --i) {
+			const float peak = peaks[i];
+			cairo_line_to(cr, i * scale, mid_y - (peak / 2.0f) * size.height);
+		}
+
+		// Close shape
+		cairo_line_to(cr, 0, mid_y);
+
+		cairo_set_source_gdk(cr, widget->style->mid);
+		cairo_fill_preserve(cr);
+
+		cairo_set_source_gdk(cr, widget->style->fg);
+		cairo_stroke(cr);
+	}
+
+	cairo_destroy(cr);
+	return TRUE;
 }
 
 static LV2UI_Handle
@@ -104,6 +176,7 @@ instantiate(const LV2UI_Descriptor*   descriptor,
 
 	ui->write      = write_function;
 	ui->controller = controller;
+	ui->width      = MIN_CANVAS_W;
 	*widget        = NULL;
 
 	// Get host features
@@ -122,21 +195,25 @@ instantiate(const LV2UI_Descriptor*   descriptor,
 	// Map URIs and initialise forge
 	map_sampler_uris(ui->map, &ui->uris);
 	lv2_atom_forge_init(&ui->forge, ui->map);
+	peaks_receiver_init(&ui->precv, ui->map);
 
 	// Construct Gtk UI
 	ui->box = gtk_vbox_new(FALSE, 4);
-	ui->label = gtk_label_new("?");
-	ui->button = gtk_button_new_with_label("Load Sample");
-	gtk_box_pack_start(GTK_BOX(ui->box), ui->label, TRUE, TRUE, 4);
-	gtk_box_pack_start(GTK_BOX(ui->box), ui->button, FALSE, FALSE, 4);
-	g_signal_connect(ui->button, "clicked",
-	                 G_CALLBACK(on_load_clicked),
+	ui->button = gtk_file_chooser_button_new("Load Sample", GTK_FILE_CHOOSER_ACTION_OPEN);
+	ui->canvas = gtk_drawing_area_new();
+	gtk_widget_set_size_request(ui->canvas, MIN_CANVAS_W, MIN_CANVAS_H);
+	gtk_container_set_border_width(GTK_CONTAINER(ui->box), 4);
+	gtk_box_pack_start(GTK_BOX(ui->box), ui->canvas, TRUE, TRUE, 0);
+	gtk_box_pack_start(GTK_BOX(ui->box), ui->button, FALSE, TRUE, 0);
+	g_signal_connect(ui->button, "file-set",
+	                 G_CALLBACK(on_file_set),
+	                 ui);
+	g_signal_connect(G_OBJECT(ui->canvas), "expose_event",
+	                 G_CALLBACK(on_canvas_expose),
 	                 ui);
 
 	// Request state (filename) from plugin
-	uint8_t get_buf[512];
-	lv2_atom_forge_set_buffer(&ui->forge, get_buf, sizeof(get_buf));
-
+	lv2_atom_forge_set_buffer(&ui->forge, ui->forge_buf, sizeof(ui->forge_buf));
 	LV2_Atom_Forge_Frame frame;
 	LV2_Atom*            msg = (LV2_Atom*)lv2_atom_forge_object(
 		&ui->forge, &frame, 0, ui->uris.patch_Get);
@@ -171,11 +248,21 @@ port_event(LV2UI_Handle handle,
 		const LV2_Atom* atom = (const LV2_Atom*)buffer;
 		if (lv2_atom_forge_is_object_type(&ui->forge, atom->type)) {
 			const LV2_Atom_Object* obj = (const LV2_Atom_Object*)atom;
-			const char*            uri = read_set_file(&ui->uris, obj);
-			if (uri) {
-				gtk_label_set_text(GTK_LABEL(ui->label), uri);
-			} else {
-				lv2_log_warning(&ui->logger, "Malformed message\n");
+			if (obj->body.otype == ui->uris.patch_Set) {
+				const char* path = read_set_file(&ui->uris, obj);
+				if (path && (!ui->filename || strcmp(path, ui->filename))) {
+					g_free(ui->filename);
+					ui->filename = g_strdup(path);
+					gtk_file_chooser_set_filename(GTK_FILE_CHOOSER(ui->button), path);
+					peaks_receiver_clear(&ui->precv);
+					request_peaks(ui, ui->width / 2 * 2);
+				} else if (!path) {
+					lv2_log_warning(&ui->logger, "Set message has no path\n");
+				}
+			} else if (obj->body.otype == ui->precv.uris.peaks_PeakUpdate) {
+				if (!peaks_receiver_receive(&ui->precv, obj)) {
+					gtk_widget_queue_draw(ui->canvas);
+				}
 			}
 		} else {
 			lv2_log_error(&ui->logger, "Unknown message type\n");
diff --git a/plugins/eg-sampler.lv2/uris.h b/plugins/eg-sampler.lv2/uris.h
index ceeddc0..9e44cf4 100644
--- a/plugins/eg-sampler.lv2/uris.h
+++ b/plugins/eg-sampler.lv2/uris.h
@@ -24,9 +24,9 @@
 #include "lv2/lv2plug.in/ns/ext/parameters/parameters.h"
 
 #define EG_SAMPLER_URI          "http://lv2plug.in/plugins/eg-sampler"
-#define EG_SAMPLER__sample      EG_SAMPLER_URI "#sample"
 #define EG_SAMPLER__applySample EG_SAMPLER_URI "#applySample"
 #define EG_SAMPLER__freeSample  EG_SAMPLER_URI "#freeSample"
+#define EG_SAMPLER__sample      EG_SAMPLER_URI "#sample"
 
 typedef struct {
 	LV2_URID atom_Float;
@@ -36,12 +36,13 @@ typedef struct {
 	LV2_URID atom_URID;
 	LV2_URID atom_eventTransfer;
 	LV2_URID eg_applySample;
-	LV2_URID eg_sample;
 	LV2_URID eg_freeSample;
+	LV2_URID eg_sample;
 	LV2_URID midi_Event;
 	LV2_URID param_gain;
 	LV2_URID patch_Get;
 	LV2_URID patch_Set;
+	LV2_URID patch_accept;
 	LV2_URID patch_property;
 	LV2_URID patch_value;
 } SamplerURIs;
@@ -62,17 +63,21 @@ map_sampler_uris(LV2_URID_Map* map, SamplerURIs* uris)
 	uris->param_gain         = map->map(map->handle, LV2_PARAMETERS__gain);
 	uris->patch_Get          = map->map(map->handle, LV2_PATCH__Get);
 	uris->patch_Set          = map->map(map->handle, LV2_PATCH__Set);
+	uris->patch_accept       = map->map(map->handle, LV2_PATCH__accept);
 	uris->patch_property     = map->map(map->handle, LV2_PATCH__property);
 	uris->patch_value        = map->map(map->handle, LV2_PATCH__value);
 }
 
 /**
- * Write a message like the following to @p forge:
- * []
- *     a patch:Set ;
- *     patch:property eg:sample ;
- *     patch:value </home/me/foo.wav> .
- */
+   Write a message like the following to `forge`:
+   [source,n3]
+   ----
+   []
+   a patch:Set ;
+   patch:property eg:sample ;
+   patch:value </home/me/foo.wav> .
+   ----
+*/
 static inline LV2_Atom_Forge_Ref
 write_set_file(LV2_Atom_Forge*    forge,
                const SamplerURIs* uris,
@@ -93,12 +98,15 @@ write_set_file(LV2_Atom_Forge*    forge,
 }
 
 /**
- * Get the file path from a message like:
- * []
- *     a patch:Set ;
- *     patch:property eg:sample ;
- *     patch:value </home/me/foo.wav> .
- */
+   Get the file path from `obj` which is a message like:
+   [source,n3]
+   ----
+   []
+   a patch:Set ;
+   patch:property eg:sample ;
+   patch:value </home/me/foo.wav> .
+   ----
+*/
 static inline const char*
 read_set_file(const SamplerURIs*     uris,
               const LV2_Atom_Object* obj)