Added Custom Performance Monitor and feature to read intermediate values of Monitor

Custom monitors can be added/removed/checked using `Performance.add_custom_monitor`/`Performance.remove_custom_monitor`/`Performance.has_custom_monitor`

The value can be viewed in the `Monitor` tab of Debugger.

Text before `/` is used to categorize the custom monitor.

`EditorPerformanceProfiler` class is created to separate logic from `ScriptEditorDebugger`

User can click on the graph of monitors to read the value at that point.

Graph includes intermediate base lines.

8 files changed, 708 insertions, 242 deletions

diff --git a/core/debugger/remote_debugger.cpp b/core/debugger/remote_debugger.cpp
index 62f600c5e5..9d55e1312e 100644
--- a/core/debugger/remote_debugger.cpp
+++ b/core/debugger/remote_debugger.cpp
@@ -373,6 +373,7 @@ struct RemoteDebugger::VisualProfiler {
 struct RemoteDebugger::PerformanceProfiler {
 	Object *performance = nullptr;
 	int last_perf_time = 0;
+	uint64_t last_monitor_modification_time = 0;
 
 	void toggle(bool p_enable, const Array &p_opts) {}
 	void add(const Array &p_data) {}
@@ -386,12 +387,31 @@ struct RemoteDebugger::PerformanceProfiler {
 			return;
 		}
 		last_perf_time = pt;
+
+		Array custom_monitor_names = performance->call("get_custom_monitor_names");
+
+		uint64_t monitor_modification_time = performance->call("get_monitor_modification_time");
+		if (monitor_modification_time > last_monitor_modification_time) {
+			last_monitor_modification_time = monitor_modification_time;
+			EngineDebugger::get_singleton()->send_message("performance:profile_names", custom_monitor_names);
+		}
+
 		int max = performance->get("MONITOR_MAX");
 		Array arr;
-		arr.resize(max);
+		arr.resize(max + custom_monitor_names.size());
 		for (int i = 0; i < max; i++) {
 			arr[i] = performance->call("get_monitor", i);
 		}
+
+		for (int i = 0; i < custom_monitor_names.size(); i++) {
+			Variant monitor_value = performance->call("get_custom_monitor", custom_monitor_names[i]);
+			if (!monitor_value.is_num()) {
+				ERR_PRINT("Value of custom monitor '" + String(custom_monitor_names[i]) + "' is not a number");
+				arr[i + max] = Variant();
+			}
+			arr[i + max] = monitor_value;
+		}
+
 		EngineDebugger::get_singleton()->send_message("performance:profile_frame", arr);
 	}
 
diff --git a/doc/classes/Performance.xml b/doc/classes/Performance.xml
index 2a0c153267..0a9079ce71 100644
--- a/doc/classes/Performance.xml
+++ b/doc/classes/Performance.xml
@@ -5,12 +5,55 @@
 	</brief_description>
 	<description>
 		This class provides access to a number of different monitors related to performance, such as memory usage, draw calls, and FPS. These are the same as the values displayed in the [b]Monitor[/b] tab in the editor's [b]Debugger[/b] panel. By using the [method get_monitor] method of this class, you can access this data from your code.
+		You can add custom monitors using the [method add_custom_monitor] method. Custom monitors are available in [b]Monitor[/b] tab in the editor's [b]Debugger[/b] panel together with built-in monitors.
 		[b]Note:[/b] A few of these monitors are only available in debug mode and will always return 0 when used in a release build.
 		[b]Note:[/b] Many of these monitors are not updated in real-time, so there may be a short delay between changes.
+		[b]Note:[/b] Custom monitors do not support negative values. Negative values are clamped to 0.
 	</description>
 	<tutorials>
 	</tutorials>
 	<methods>
+		<method name="add_custom_monitor">
+			<return type="void">
+			</return>
+			<argument index="0" name="id" type="StringName">
+			</argument>
+			<argument index="1" name="callable" type="Callable">
+			</argument>
+			<argument index="2" name="arguments" type="Array" default="[  ]">
+			</argument>
+			<description>
+				Adds a custom monitor with name same as id. You can specify the category of monitor using '/' in id. If there are more than one '/' then default category is used. Default category is "Custom".
+				[codeblock]
+				Performance.add_custom_monitor("MyCategory/MyMonitor", some_callable) # Adds monitor with name "MyName" to category "MyCategory"
+				Performance.add_custom_monitor("MyMonitor", some_callable) # Adds monitor with name "MyName" to category "Custom"
+				# Note: "MyCategory/MyMonitor" and "MyMonitor" have same name but different ids so above code is valid
+				Performance.add_custom_monitor("Custom/MyMonitor", some_callable) # Adds monitor with name "MyName" to category "Custom"
+				# Note: "MyMonitor" and "Custom/MyMonitor" have same name and same category but different ids so above code is valid
+				Performance.add_custom_monitor("MyCategoryOne/MyCategoryTwo/MyMonitor", some_callable) # Adds monitor with name "MyCategoryOne/MyCategoryTwo/MyMonitor" to category "Custom"
+				[/codeblock]
+				The debugger calls the callable to get the value of custom monitor. The callable must return a number.
+				Callables are called with arguments supplied in argument array.
+				[b]Note:[/b] It throws an error if given id is already present.
+			</description>
+		</method>
+		<method name="get_custom_monitor">
+			<return type="Variant">
+			</return>
+			<argument index="0" name="id" type="StringName">
+			</argument>
+			<description>
+				Returns the value of custom monitor with given id. The callable is called to get the value of custom monitor.
+				[b]Note:[/b] It throws an error if the given id is absent.
+			</description>
+		</method>
+		<method name="get_custom_monitor_names">
+			<return type="Array">
+			</return>
+			<description>
+				Returns the names of active custom monitors in an array.
+			</description>
+		</method>
 		<method name="get_monitor" qualifiers="const">
 			<return type="float">
 			</return>
@@ -23,6 +66,32 @@
 				[/codeblock]
 			</description>
 		</method>
+		<method name="get_monitor_modification_time">
+			<return type="int">
+			</return>
+			<description>
+				Returns the last tick in which custom monitor was added/removed.
+			</description>
+		</method>
+		<method name="has_custom_monitor">
+			<return type="bool">
+			</return>
+			<argument index="0" name="id" type="StringName">
+			</argument>
+			<description>
+				Returns true if custom monitor with the given id is present otherwise returns false.
+			</description>
+		</method>
+		<method name="remove_custom_monitor">
+			<return type="void">
+			</return>
+			<argument index="0" name="id" type="StringName">
+			</argument>
+			<description>
+				Removes the custom monitor with given id.
+				[b]Note:[/b] It throws an error if the given id is already absent.
+			</description>
+		</method>
 	</methods>
 	<constants>
 		<constant name="TIME_FPS" value="0" enum="Monitor">
diff --git a/editor/debugger/editor_performance_profiler.cpp b/editor/debugger/editor_performance_profiler.cpp
new file mode 100644
index 0000000000..47fe282758
--- /dev/null
+++ b/editor/debugger/editor_performance_profiler.cpp
@@ -0,0 +1,394 @@
+/*************************************************************************/
+/*  editor_performance_profiler.cpp                                      */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "editor_performance_profiler.h"
+
+#include "editor/editor_scale.h"
+#include "editor/editor_settings.h"
+#include "main/performance.h"
+
+EditorPerformanceProfiler::Monitor::Monitor() {}
+
+EditorPerformanceProfiler::Monitor::Monitor(String p_name, String p_base, int p_frame_index, Performance::MonitorType p_type, TreeItem *p_item) {
+	type = p_type;
+	item = p_item;
+	frame_index = p_frame_index;
+	name = p_name;
+	base = p_base;
+}
+
+void EditorPerformanceProfiler::Monitor::update_value(float p_value) {
+	ERR_FAIL_COND(!item);
+	String label = EditorPerformanceProfiler::_create_label(p_value, type);
+	String tooltip = label;
+	switch (type) {
+		case Performance::MONITOR_TYPE_MEMORY: {
+			tooltip = label;
+		} break;
+		case Performance::MONITOR_TYPE_TIME: {
+			tooltip = label;
+		} break;
+		default: {
+			tooltip += " " + item->get_text(0);
+		} break;
+	}
+	item->set_text(1, label);
+	item->set_tooltip(1, tooltip);
+
+	if (p_value > max) {
+		max = p_value;
+	}
+}
+
+void EditorPerformanceProfiler::Monitor::reset() {
+	history.clear();
+	max = 0.0f;
+	if (item) {
+		item->set_text(1, "");
+		item->set_tooltip(1, "");
+	}
+}
+
+String EditorPerformanceProfiler::_create_label(float p_value, Performance::MonitorType p_type) {
+	switch (p_type) {
+		case Performance::MONITOR_TYPE_MEMORY: {
+			return String::humanize_size(p_value);
+		}
+		case Performance::MONITOR_TYPE_TIME: {
+			return rtos(p_value * 1000).pad_decimals(2) + " ms";
+		}
+		default: {
+			return rtos(p_value);
+		}
+	}
+}
+
+void EditorPerformanceProfiler::_monitor_select() {
+	monitor_draw->update();
+}
+
+void EditorPerformanceProfiler::_monitor_draw() {
+	Vector<StringName> active;
+	for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+		if (i.value().item->is_checked(0)) {
+			active.push_back(i.key());
+		}
+	}
+
+	if (active.empty()) {
+		info_message->show();
+		return;
+	}
+
+	info_message->hide();
+
+	Ref<StyleBox> graph_style_box = get_theme_stylebox("normal", "TextEdit");
+	Ref<Font> graph_font = get_theme_font("font", "TextEdit");
+
+	int columns = int(Math::ceil(Math::sqrt(float(active.size()))));
+	int rows = int(Math::ceil(float(active.size()) / float(columns)));
+	if (active.size() == 1) {
+		rows = 1;
+	}
+	Size2i cell_size = Size2i(monitor_draw->get_size()) / Size2i(columns, rows);
+	float spacing = float(POINT_SEPARATION) / float(columns);
+	float value_multiplier = EditorSettings::get_singleton()->is_dark_theme() ? 1.4f : 0.55f;
+	float hue_shift = 1.0f / float(monitors.size());
+
+	for (int i = 0; i < active.size(); i++) {
+		Monitor &current = monitors[active[i]];
+		Rect2i rect(Point2i(i % columns, i / columns) * cell_size + Point2i(MARGIN, MARGIN), cell_size - Point2i(MARGIN, MARGIN) * 2);
+		monitor_draw->draw_style_box(graph_style_box, rect);
+
+		rect.position += graph_style_box->get_offset();
+		rect.size -= graph_style_box->get_minimum_size();
+		Color draw_color = get_theme_color("accent_color", "Editor");
+		draw_color.set_hsv(Math::fmod(hue_shift * float(current.frame_index), 0.9f), draw_color.get_s() * 0.9f, draw_color.get_v() * value_multiplier, 0.6f);
+		monitor_draw->draw_string(graph_font, rect.position + Point2(0, graph_font->get_ascent()), current.item->get_text(0), draw_color, rect.size.x);
+
+		draw_color.a = 0.9f;
+		float value_position = rect.size.width - graph_font->get_string_size(current.item->get_text(1)).width;
+		if (value_position < 0) {
+			value_position = 0;
+		}
+		monitor_draw->draw_string(graph_font, rect.position + Point2(value_position, graph_font->get_ascent()), current.item->get_text(1), draw_color, rect.size.x);
+
+		rect.position.y += graph_font->get_height();
+		rect.size.height -= graph_font->get_height();
+
+		int line_count = rect.size.height / (graph_font->get_height() * 2);
+		if (line_count > 5) {
+			line_count = 5;
+		}
+		if (line_count > 0) {
+			Color horizontal_line_color;
+			horizontal_line_color.set_hsv(draw_color.get_h(), draw_color.get_s() * 0.5f, draw_color.get_v() * 0.5f, 0.3f);
+			monitor_draw->draw_line(rect.position, rect.position + Vector2(rect.size.width, 0), horizontal_line_color, Math::round(EDSCALE));
+			monitor_draw->draw_string(graph_font, rect.position + Vector2(0, graph_font->get_ascent()), _create_label(current.max, current.type), horizontal_line_color, rect.size.width);
+
+			for (int j = 0; j < line_count; j++) {
+				Vector2 y_offset = Vector2(0, rect.size.height * (1.0f - float(j) / float(line_count)));
+				monitor_draw->draw_line(rect.position + y_offset, rect.position + Vector2(rect.size.width, 0) + y_offset, horizontal_line_color, Math::round(EDSCALE));
+				monitor_draw->draw_string(graph_font, rect.position - Vector2(0, graph_font->get_descent()) + y_offset, _create_label(current.max * float(j) / float(line_count), current.type), horizontal_line_color, rect.size.width);
+			}
+		}
+
+		float from = rect.size.width;
+		float prev = -1.0f;
+		int count = 0;
+		List<float>::Element *e = current.history.front();
+
+		while (from >= 0 && e) {
+			float m = current.max;
+			float h2 = 0;
+			if (m != 0) {
+				h2 = (e->get() / m);
+			}
+			h2 = (1.0f - h2) * float(rect.size.y);
+			if (e != current.history.front()) {
+				monitor_draw->draw_line(rect.position + Point2(from, h2), rect.position + Point2(from + spacing, prev), draw_color, Math::round(EDSCALE));
+			}
+
+			if (marker_key == active[i] && count == marker_frame) {
+				Color line_color;
+				line_color.set_hsv(draw_color.get_h(), draw_color.get_s() * 0.8f, draw_color.get_v(), 0.5f);
+				monitor_draw->draw_line(rect.position + Point2(from, 0), rect.position + Point2(from, rect.size.y), line_color, Math::round(EDSCALE));
+
+				String label = _create_label(e->get(), current.type);
+				Size2 size = graph_font->get_string_size(label);
+				Vector2 text_top_left_position = Vector2(from, h2) - (size + Vector2(MARKER_MARGIN, MARKER_MARGIN));
+				if (text_top_left_position.x < 0) {
+					text_top_left_position.x = from + MARKER_MARGIN;
+				}
+				if (text_top_left_position.y < 0) {
+					text_top_left_position.y = h2 + MARKER_MARGIN;
+				}
+				monitor_draw->draw_string(graph_font, rect.position + text_top_left_position + Point2(0, graph_font->get_ascent()), label, line_color, rect.size.x);
+			}
+			prev = h2;
+			e = e->next();
+			from -= spacing;
+			count++;
+		}
+	}
+}
+
+void EditorPerformanceProfiler::_build_monitor_tree() {
+	Set<StringName> monitor_checked;
+	for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+		if (i.value().item && i.value().item->is_checked(0)) {
+			monitor_checked.insert(i.key());
+		}
+	}
+
+	base_map.clear();
+	monitor_tree->get_root()->clear_children();
+
+	for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+		TreeItem *base = _get_monitor_base(i.value().base);
+		TreeItem *item = _create_monitor_item(i.value().name, base);
+		item->set_checked(0, monitor_checked.has(i.key()));
+		i.value().item = item;
+		if (!i.value().history.empty()) {
+			i.value().update_value(i.value().history.front()->get());
+		}
+	}
+}
+
+TreeItem *EditorPerformanceProfiler::_get_monitor_base(const StringName &p_base_name) {
+	if (base_map.has(p_base_name)) {
+		return base_map[p_base_name];
+	}
+
+	TreeItem *base = monitor_tree->create_item(monitor_tree->get_root());
+	base->set_text(0, p_base_name);
+	base->set_editable(0, false);
+	base->set_selectable(0, false);
+	base->set_expand_right(0, true);
+	base_map.insert(p_base_name, base);
+	return base;
+}
+
+TreeItem *EditorPerformanceProfiler::_create_monitor_item(const StringName &p_monitor_name, TreeItem *p_base) {
+	TreeItem *item = monitor_tree->create_item(p_base);
+	item->set_cell_mode(0, TreeItem::CELL_MODE_CHECK);
+	item->set_editable(0, true);
+	item->set_selectable(0, false);
+	item->set_selectable(1, false);
+	item->set_text(0, p_monitor_name);
+	return item;
+}
+
+void EditorPerformanceProfiler::_marker_input(const Ref<InputEvent> &p_event) {
+	Ref<InputEventMouseButton> mb = p_event;
+	if (mb.is_valid() && mb->is_pressed() && mb->get_button_index() == BUTTON_LEFT) {
+		Vector<StringName> active;
+		for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+			if (i.value().item->is_checked(0)) {
+				active.push_back(i.key());
+			}
+		}
+		if (active.size() > 0) {
+			int columns = int(Math::ceil(Math::sqrt(float(active.size()))));
+			int rows = int(Math::ceil(float(active.size()) / float(columns)));
+			if (active.size() == 1) {
+				rows = 1;
+			}
+			Size2i cell_size = Size2i(monitor_draw->get_size()) / Size2i(columns, rows);
+			Vector2i index = mb->get_position() / cell_size;
+			Rect2i rect(index * cell_size + Point2i(MARGIN, MARGIN), cell_size - Point2i(MARGIN, MARGIN) * 2);
+			if (rect.has_point(mb->get_position())) {
+				if (index.x + index.y * columns < active.size()) {
+					marker_key = active[index.x + index.y * columns];
+				} else {
+					marker_key = "";
+				}
+				Ref<StyleBox> graph_style_box = get_theme_stylebox("normal", "TextEdit");
+				rect.position += graph_style_box->get_offset();
+				rect.size -= graph_style_box->get_minimum_size();
+				Vector2 point = mb->get_position() - rect.position;
+				if (point.x >= rect.size.x) {
+					marker_frame = 0;
+				} else {
+					int point_sep = 5;
+					float spacing = float(point_sep) / float(columns);
+					marker_frame = (rect.size.x - point.x) / spacing;
+				}
+				monitor_draw->update();
+				return;
+			}
+		}
+		marker_key = "";
+		monitor_draw->update();
+	}
+}
+
+void EditorPerformanceProfiler::reset() {
+	for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+		if (String(i.key()).begins_with("custom:")) {
+			monitors.erase(i);
+		} else {
+			i.value().reset();
+		}
+	}
+
+	_build_monitor_tree();
+	marker_key = "";
+	marker_frame = 0;
+	monitor_draw->update();
+}
+
+void EditorPerformanceProfiler::update_monitors(const Vector<StringName> &p_names) {
+	OrderedHashMap<StringName, int> names;
+	for (int i = 0; i < p_names.size(); i++) {
+		names.insert("custom:" + p_names[i], Performance::MONITOR_MAX + i);
+	}
+
+	for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+		if (String(i.key()).begins_with("custom:")) {
+			if (!names.has(i.key())) {
+				monitors.erase(i);
+			} else {
+				i.value().frame_index = names[i.key()];
+				names.erase(i.key());
+			}
+		}
+	}
+
+	for (OrderedHashMap<StringName, int>::Element i = names.front(); i; i = i.next()) {
+		String name = String(i.key()).replace_first("custom:", "");
+		String base = "Custom";
+		if (name.get_slice_count("/") == 2) {
+			base = name.get_slicec('/', 0);
+			name = name.get_slicec('/', 1);
+		}
+		monitors.insert(i.key(), Monitor(name, base, i.value(), Performance::MONITOR_TYPE_QUANTITY, nullptr));
+	}
+
+	_build_monitor_tree();
+}
+
+void EditorPerformanceProfiler::add_profile_frame(const Vector<float> &p_values) {
+	for (OrderedHashMap<StringName, Monitor>::Element i = monitors.front(); i; i = i.next()) {
+		float data = 0.0f;
+		if (i.value().frame_index >= 0 && i.value().frame_index < p_values.size()) {
+			data = p_values[i.value().frame_index];
+		}
+		i.value().history.push_front(data);
+		i.value().update_value(data);
+	}
+	marker_frame++;
+	monitor_draw->update();
+}
+
+List<float> *EditorPerformanceProfiler::get_monitor_data(const StringName &p_name) {
+	if (monitors.has(p_name)) {
+		return &monitors[p_name].history;
+	}
+	return nullptr;
+}
+
+EditorPerformanceProfiler::EditorPerformanceProfiler() {
+	set_name(TTR("Monitors"));
+	set_split_offset(340 * EDSCALE);
+
+	monitor_tree = memnew(Tree);
+	monitor_tree->set_columns(2);
+	monitor_tree->set_column_title(0, TTR("Monitor"));
+	monitor_tree->set_column_title(1, TTR("Value"));
+	monitor_tree->set_column_titles_visible(true);
+	monitor_tree->connect("item_edited", callable_mp(this, &EditorPerformanceProfiler::_monitor_select));
+	monitor_tree->create_item();
+	monitor_tree->set_hide_root(true);
+	add_child(monitor_tree);
+
+	monitor_draw = memnew(Control);
+	monitor_draw->set_clip_contents(true);
+	monitor_draw->connect("draw", callable_mp(this, &EditorPerformanceProfiler::_monitor_draw));
+	monitor_draw->connect("gui_input", callable_mp(this, &EditorPerformanceProfiler::_marker_input));
+	add_child(monitor_draw);
+
+	info_message = memnew(Label);
+	info_message->set_text(TTR("Pick one or more items from the list to display the graph."));
+	info_message->set_valign(Label::VALIGN_CENTER);
+	info_message->set_align(Label::ALIGN_CENTER);
+	info_message->set_autowrap(true);
+	info_message->set_custom_minimum_size(Size2(100 * EDSCALE, 0));
+	info_message->set_anchors_and_margins_preset(PRESET_WIDE, PRESET_MODE_KEEP_SIZE, 8 * EDSCALE);
+	monitor_draw->add_child(info_message);
+
+	for (int i = 0; i < Performance::MONITOR_MAX; i++) {
+		String base = Performance::get_singleton()->get_monitor_name(Performance::Monitor(i)).get_slicec('/', 0).capitalize();
+		String name = Performance::get_singleton()->get_monitor_name(Performance::Monitor(i)).get_slicec('/', 1).capitalize();
+		monitors.insert(Performance::get_singleton()->get_monitor_name(Performance::Monitor(i)), Monitor(name, base, i, Performance::get_singleton()->get_monitor_type(Performance::Monitor(i)), nullptr));
+	}
+
+	_build_monitor_tree();
+}
diff --git a/editor/debugger/editor_performance_profiler.h b/editor/debugger/editor_performance_profiler.h
new file mode 100644
index 0000000000..144dd34103
--- /dev/null
+++ b/editor/debugger/editor_performance_profiler.h
@@ -0,0 +1,90 @@
+/*************************************************************************/
+/*  editor_performance_profiler.h                                        */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef EDITOR_PERFORMANCE_PROFILER_H
+#define EDITOR_PERFORMANCE_PROFILER_H
+
+#include "core/map.h"
+#include "core/ordered_hash_map.h"
+#include "main/performance.h"
+#include "scene/gui/control.h"
+#include "scene/gui/label.h"
+#include "scene/gui/split_container.h"
+#include "scene/gui/tree.h"
+
+class EditorPerformanceProfiler : public HSplitContainer {
+	GDCLASS(EditorPerformanceProfiler, HSplitContainer);
+
+private:
+	class Monitor {
+	public:
+		String name;
+		String base;
+		List<float> history;
+		float max = 0.0f;
+		TreeItem *item = nullptr;
+		Performance::MonitorType type = Performance::MONITOR_TYPE_QUANTITY;
+		int frame_index = 0;
+
+		Monitor();
+		Monitor(String p_name, String p_base, int p_frame_index, Performance::MonitorType p_type, TreeItem *p_item);
+		void update_value(float p_value);
+		void reset();
+	};
+
+	OrderedHashMap<StringName, Monitor> monitors;
+
+	Map<StringName, TreeItem *> base_map;
+	Tree *monitor_tree;
+	Control *monitor_draw;
+	Label *info_message;
+	StringName marker_key;
+	int marker_frame;
+	const int MARGIN = 4;
+	const int POINT_SEPARATION = 5;
+	const int MARKER_MARGIN = 2;
+
+	static String _create_label(float p_value, Performance::MonitorType p_type);
+	void _monitor_select();
+	void _monitor_draw();
+	void _build_monitor_tree();
+	TreeItem *_get_monitor_base(const StringName &p_base_name);
+	TreeItem *_create_monitor_item(const StringName &p_monitor_name, TreeItem *p_base);
+	void _marker_input(const Ref<InputEvent> &p_event);
+
+public:
+	void reset();
+	void update_monitors(const Vector<StringName> &p_names);
+	void add_profile_frame(const Vector<float> &p_values);
+	List<float> *get_monitor_data(const StringName &p_name);
+	EditorPerformanceProfiler();
+};
+
+#endif // EDITOR_PERFORMANCE_PROFILER_H
diff --git a/editor/debugger/script_editor_debugger.cpp b/editor/debugger/script_editor_debugger.cpp
index 6b010fbfb5..a828e29558 100644
--- a/editor/debugger/script_editor_debugger.cpp
+++ b/editor/debugger/script_editor_debugger.cpp
@@ -36,6 +36,7 @@
 #include "core/project_settings.h"
 #include "core/ustring.h"
 #include "editor/debugger/editor_network_profiler.h"
+#include "editor/debugger/editor_performance_profiler.h"
 #include "editor/debugger/editor_profiler.h"
 #include "editor/debugger/editor_visual_profiler.h"
 #include "editor/editor_log.h"
@@ -172,14 +173,25 @@ void ScriptEditorDebugger::_file_selected(const String &p_file) {
 			file->store_csv_line(line);
 
 			// values
-			List<Vector<float>>::Element *E = perf_history.back();
-			while (E) {
-				Vector<float> &perf_data = E->get();
-				for (int i = 0; i < perf_data.size(); i++) {
-					line.write[i] = String::num_real(perf_data[i]);
+			Vector<List<float>::Element *> iterators;
+			iterators.resize(Performance::MONITOR_MAX);
+			bool continue_iteration = false;
+			for (int i = 0; i < Performance::MONITOR_MAX; i++) {
+				iterators.write[i] = performance_profiler->get_monitor_data(Performance::get_singleton()->get_monitor_name(Performance::Monitor(i)))->back();
+				continue_iteration = continue_iteration || iterators[i];
+			}
+			while (continue_iteration) {
+				continue_iteration = false;
+				for (int i = 0; i < Performance::MONITOR_MAX; i++) {
+					if (iterators[i]) {
+						line.write[i] = String::num_real(iterators[i]->get());
+						iterators.write[i] = iterators[i]->prev();
+					} else {
+						line.write[i] = "";
+					}
+					continue_iteration = continue_iteration || iterators[i];
 				}
 				file->store_csv_line(line);
-				E = E->prev();
 			}
 			file->store_string("\n");
 
@@ -409,37 +421,12 @@ void ScriptEditorDebugger::_parse_message(const String &p_msg, const Array &p_da
 			EditorNode::get_log()->add_message(output_strings[i], msg_type);
 		}
 	} else if (p_msg == "performance:profile_frame") {
-		Vector<float> p;
-		p.resize(p_data.size());
+		Vector<float> frame_data;
+		frame_data.resize(p_data.size());
 		for (int i = 0; i < p_data.size(); i++) {
-			p.write[i] = p_data[i];
-			if (i < perf_items.size()) {
-				const float value = p[i];
-				String label = rtos(value);
-				String tooltip = label;
-				switch (Performance::MonitorType((int)perf_items[i]->get_metadata(1))) {
-					case Performance::MONITOR_TYPE_MEMORY: {
-						label = String::humanize_size(value);
-						tooltip = label;
-					} break;
-					case Performance::MONITOR_TYPE_TIME: {
-						label = rtos(value * 1000).pad_decimals(2) + " ms";
-						tooltip = label;
-					} break;
-					default: {
-						tooltip += " " + perf_items[i]->get_text(0);
-					} break;
-				}
-
-				perf_items[i]->set_text(1, label);
-				perf_items[i]->set_tooltip(1, tooltip);
-				if (p[i] > perf_max[i]) {
-					perf_max.write[i] = p[i];
-				}
-			}
+			frame_data.write[i] = p_data[i];
 		}
-		perf_history.push_front(p);
-		perf_draw->update();
+		performance_profiler->add_profile_frame(frame_data);
 
 	} else if (p_msg == "visual:profile_frame") {
 		DebuggerMarshalls::VisualProfilerFrame frame;
@@ -704,6 +691,15 @@ void ScriptEditorDebugger::_parse_message(const String &p_msg, const Array &p_da
 		emit_signal("stop_requested");
 		_stop_and_notify();
 
+	} else if (p_msg == "performance:profile_names") {
+		Vector<StringName> monitors;
+		monitors.resize(p_data.size());
+		for (int i = 0; i < p_data.size(); i++) {
+			ERR_FAIL_COND(p_data[i].get_type() != Variant::STRING_NAME);
+			monitors.set(i, p_data[i]);
+		}
+		performance_profiler->update_monitors(monitors);
+
 	} else {
 		WARN_PRINT("unknown message " + p_msg);
 	}
@@ -724,141 +720,6 @@ void ScriptEditorDebugger::_set_reason_text(const String &p_reason, MessageType
 	reason->set_tooltip(p_reason.word_wrap(80));
 }
 
-void ScriptEditorDebugger::_performance_select() {
-	perf_draw->update();
-}
-
-void ScriptEditorDebugger::_performance_draw() {
-	Vector<int> which;
-	for (int i = 0; i < perf_items.size(); i++) {
-		if (perf_items[i]->is_checked(0)) {
-			which.push_back(i);
-		}
-	}
-
-	if (which.empty()) {
-		info_message->show();
-		return;
-	}
-
-	info_message->hide();
-
-	const Ref<StyleBox> graph_sb = get_theme_stylebox("normal", "TextEdit");
-	const Ref<Font> graph_font = get_theme_font("font", "TextEdit");
-
-	const int cols = Math::ceil(Math::sqrt((float)which.size()));
-	int rows = Math::ceil((float)which.size() / cols);
-	if (which.size() == 1) {
-		rows = 1;
-	}
-
-	const int margin = 3;
-	const int point_sep = 5;
-	const Size2i s = Size2i(perf_draw->get_size()) / Size2i(cols, rows);
-
-	for (int i = 0; i < which.size(); i++) {
-		Point2i p(i % cols, i / cols);
-		Rect2i r(p * s, s);
-		r.position += Point2(margin, margin);
-		r.size -= Point2(margin, margin) * 2.0;
-		perf_draw->draw_style_box(graph_sb, r);
-		r.position += graph_sb->get_offset();
-		r.size -= graph_sb->get_minimum_size();
-		const int pi = which[i];
-
-		// Draw horizontal lines with labels.
-
-		int nb_lines = 5;
-		// Draw less lines if the monitor isn't tall enough to display 5 labels.
-		if (r.size.height <= 160 * EDSCALE) {
-			nb_lines = 3;
-		} else if (r.size.height <= 240 * EDSCALE) {
-			nb_lines = 4;
-		}
-
-		const float inv_nb_lines = 1.0 / nb_lines;
-
-		for (int line = 0; line < nb_lines; line += 1) {
-			const int from_x = r.position.x;
-			const int to_x = r.position.x + r.size.width;
-			const int y = r.position.y + (r.size.height * inv_nb_lines + line * inv_nb_lines * r.size.height);
-			perf_draw->draw_line(
-					Point2(from_x, y),
-					Point2i(to_x, y),
-					Color(0.5, 0.5, 0.5, 0.25),
-					Math::round(EDSCALE));
-
-			String label;
-			switch (Performance::MonitorType((int)perf_items[pi]->get_metadata(1))) {
-				case Performance::MONITOR_TYPE_MEMORY: {
-					label = String::humanize_size(Math::ceil((1 - inv_nb_lines - inv_nb_lines * line) * perf_max[pi]));
-				} break;
-				case Performance::MONITOR_TYPE_TIME: {
-					label = rtos((1 - inv_nb_lines - inv_nb_lines * line) * perf_max[pi] * 1000).pad_decimals(2) + " ms";
-				} break;
-				default: {
-					label = itos(Math::ceil((1 - inv_nb_lines - inv_nb_lines * line) * perf_max[pi]));
-				} break;
-			}
-
-			perf_draw->draw_string(
-					graph_font,
-					Point2(from_x, y - graph_font->get_ascent() * 0.25),
-					label,
-					Color(0.5, 0.5, 0.5, 1.0));
-		}
-
-		const float h = (float)which[i] / (float)(perf_items.size());
-		// Use a darker color on light backgrounds for better visibility.
-		const float value_multiplier = EditorSettings::get_singleton()->is_dark_theme() ? 1.4 : 0.55;
-		Color color = get_theme_color("accent_color", "Editor");
-		color.set_hsv(Math::fmod(h + 0.4, 0.9), color.get_s() * 0.9, color.get_v() * value_multiplier);
-
-		// Draw the monitor name in the top-left corner.
-		color.a = 0.6;
-		perf_draw->draw_string(
-				graph_font,
-				r.position + Point2(0, graph_font->get_ascent()),
-				perf_items[pi]->get_text(0),
-				color,
-				r.size.x);
-
-		// Draw the monitor value in the top-left corner, just below the name.
-		color.a = 0.9;
-		perf_draw->draw_string(
-				graph_font,
-				r.position + Point2(0, graph_font->get_ascent() + graph_font->get_height()),
-				perf_items[pi]->get_text(1),
-				color,
-				r.size.y);
-
-		const float spacing = point_sep / float(cols);
-		float from = r.size.width;
-
-		const List<Vector<float>>::Element *E = perf_history.front();
-		float prev = -1;
-		while (from >= 0 && E) {
-			float m = perf_max[pi];
-			if (m == 0) {
-				m = 0.00001;
-			}
-			float h2 = E->get()[pi] / m;
-			h2 = (1.0 - h2) * r.size.y;
-
-			if (E != perf_history.front()) {
-				perf_draw->draw_line(
-						r.position + Point2(from, h2),
-						r.position + Point2(from + spacing, prev),
-						color,
-						Math::round(EDSCALE));
-			}
-			prev = h2;
-			E = E->next();
-			from -= spacing;
-		}
-	}
-}
-
 void ScriptEditorDebugger::_notification(int p_what) {
 	switch (p_what) {
 		case NOTIFICATION_ENTER_TREE: {
@@ -976,10 +837,7 @@ void ScriptEditorDebugger::start(Ref<RemoteDebuggerPeer> p_peer) {
 	peer = p_peer;
 	ERR_FAIL_COND(p_peer.is_null());
 
-	perf_history.clear();
-	for (int i = 0; i < Performance::MONITOR_MAX; i++) {
-		perf_max.write[i] = 0;
-	}
+	performance_profiler->reset();
 
 	set_process(true);
 	breaked = false;
@@ -1727,63 +1585,8 @@ ScriptEditorDebugger::ScriptEditorDebugger(EditorNode *p_editor) {
 	}
 
 	{ //monitors
-
-		HSplitContainer *hsp = memnew(HSplitContainer);
-
-		perf_monitors = memnew(Tree);
-		perf_monitors->set_columns(2);
-		perf_monitors->set_column_title(0, TTR("Monitor"));
-		perf_monitors->set_column_title(1, TTR("Value"));
-		perf_monitors->set_column_titles_visible(true);
-		perf_monitors->connect("item_edited", callable_mp(this, &ScriptEditorDebugger::_performance_select));
-		hsp->add_child(perf_monitors);
-
-		perf_draw = memnew(Control);
-		perf_draw->set_clip_contents(true);
-		perf_draw->connect("draw", callable_mp(this, &ScriptEditorDebugger::_performance_draw));
-		hsp->add_child(perf_draw);
-
-		hsp->set_name(TTR("Monitors"));
-		hsp->set_split_offset(340 * EDSCALE);
-		tabs->add_child(hsp);
-		perf_max.resize(Performance::MONITOR_MAX);
-
-		Map<String, TreeItem *> bases;
-		TreeItem *root = perf_monitors->create_item();
-		perf_monitors->set_hide_root(true);
-		for (int i = 0; i < Performance::MONITOR_MAX; i++) {
-			String n = Performance::get_singleton()->get_monitor_name(Performance::Monitor(i));
-			Performance::MonitorType mtype = Performance::get_singleton()->get_monitor_type(Performance::Monitor(i));
-			String base = n.get_slice("/", 0);
-			String name = n.get_slice("/", 1);
-			if (!bases.has(base)) {
-				TreeItem *b = perf_monitors->create_item(root);
-				b->set_text(0, base.capitalize());
-				b->set_editable(0, false);
-				b->set_selectable(0, false);
-				b->set_expand_right(0, true);
-				bases[base] = b;
-			}
-
-			TreeItem *it = perf_monitors->create_item(bases[base]);
-			it->set_metadata(1, mtype);
-			it->set_cell_mode(0, TreeItem::CELL_MODE_CHECK);
-			it->set_editable(0, true);
-			it->set_selectable(0, false);
-			it->set_selectable(1, false);
-			it->set_text(0, name.capitalize());
-			perf_items.push_back(it);
-			perf_max.write[i] = 0;
-		}
-
-		info_message = memnew(Label);
-		info_message->set_text(TTR("Pick one or more items from the list to display the graph."));
-		info_message->set_valign(Label::VALIGN_CENTER);
-		info_message->set_align(Label::ALIGN_CENTER);
-		info_message->set_autowrap(true);
-		info_message->set_custom_minimum_size(Size2(100 * EDSCALE, 0));
-		info_message->set_anchors_and_margins_preset(PRESET_WIDE, PRESET_MODE_KEEP_SIZE, 8 * EDSCALE);
-		perf_draw->add_child(info_message);
+		performance_profiler = memnew(EditorPerformanceProfiler);
+		tabs->add_child(performance_profiler);
 	}
 
 	{ //vmem inspect
diff --git a/editor/debugger/script_editor_debugger.h b/editor/debugger/script_editor_debugger.h
index 2984051aa1..12fb82cc6f 100644
--- a/editor/debugger/script_editor_debugger.h
+++ b/editor/debugger/script_editor_debugger.h
@@ -52,6 +52,7 @@ class ItemList;
 class EditorProfiler;
 class EditorVisualProfiler;
 class EditorNetworkProfiler;
+class EditorPerformanceProfiler;
 class SceneDebuggerTree;
 
 class ScriptEditorDebugger : public MarginContainer {
@@ -113,16 +114,8 @@ private:
 	// Each debugger should have it's tree in the future I guess.
 	const Tree *editor_remote_tree = nullptr;
 
-	List<Vector<float>> perf_history;
-	Vector<float> perf_max;
-	Vector<TreeItem *> perf_items;
-
 	Map<int, String> profiler_signature;
 
-	Tree *perf_monitors;
-	Control *perf_draw;
-	Label *info_message;
-
 	Tree *vmem_tree;
 	Button *vmem_refresh;
 	Button *vmem_export;
@@ -141,6 +134,7 @@ private:
 	EditorProfiler *profiler;
 	EditorVisualProfiler *visual_profiler;
 	EditorNetworkProfiler *network_profiler;
+	EditorPerformanceProfiler *performance_profiler;
 
 	EditorNode *editor;
 
@@ -152,8 +146,6 @@ private:
 
 	EditorDebuggerNode::CameraOverride camera_override;
 
-	void _performance_draw();
-	void _performance_select();
 	void _stack_dump_frame_selected();
 
 	void _file_selected(const String &p_file);
diff --git a/main/performance.cpp b/main/performance.cpp
index 7e6b9fca64..7234511aeb 100644
--- a/main/performance.cpp
+++ b/main/performance.cpp
@@ -43,6 +43,12 @@ Performance *Performance::singleton = nullptr;
 
 void Performance::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_monitor", "monitor"), &Performance::get_monitor);
+	ClassDB::bind_method(D_METHOD("add_custom_monitor", "id", "callable", "arguments"), &Performance::add_custom_monitor, DEFVAL(Array()));
+	ClassDB::bind_method(D_METHOD("remove_custom_monitor", "id"), &Performance::remove_custom_monitor);
+	ClassDB::bind_method(D_METHOD("has_custom_monitor", "id"), &Performance::has_custom_monitor);
+	ClassDB::bind_method(D_METHOD("get_custom_monitor", "id"), &Performance::get_custom_monitor);
+	ClassDB::bind_method(D_METHOD("get_monitor_modification_time"), &Performance::get_monitor_modification_time);
+	ClassDB::bind_method(D_METHOD("get_custom_monitor_names"), &Performance::get_custom_monitor_names);
 
 	BIND_ENUM_CONSTANT(TIME_FPS);
 	BIND_ENUM_CONSTANT(TIME_PROCESS);
@@ -231,8 +237,78 @@ void Performance::set_physics_process_time(float p_pt) {
 	_physics_process_time = p_pt;
 }
 
+void Performance::add_custom_monitor(const StringName &p_id, const Callable &p_callable, const Vector<Variant> &p_args) {
+	ERR_FAIL_COND_MSG(has_custom_monitor(p_id), "Custom monitor with id '" + String(p_id) + "' already exists.");
+	_monitor_map.insert(p_id, MonitorCall(p_callable, p_args));
+	_monitor_modification_time = OS::get_singleton()->get_ticks_usec();
+}
+
+void Performance::remove_custom_monitor(const StringName &p_id) {
+	ERR_FAIL_COND_MSG(!has_custom_monitor(p_id), "Custom monitor with id '" + String(p_id) + "' doesn't exists.");
+	_monitor_map.erase(p_id);
+	_monitor_modification_time = OS::get_singleton()->get_ticks_usec();
+}
+
+bool Performance::has_custom_monitor(const StringName &p_id) {
+	return _monitor_map.has(p_id);
+}
+
+Variant Performance::get_custom_monitor(const StringName &p_id) {
+	ERR_FAIL_COND_V_MSG(!has_custom_monitor(p_id), Variant(), "Custom monitor with id '" + String(p_id) + "' doesn't exists.");
+	bool error;
+	String error_message;
+	Variant return_value = _monitor_map[p_id].call(error, error_message);
+	ERR_FAIL_COND_V_MSG(error, return_value, "Error calling from custom monitor '" + String(p_id) + "' to callable: " + error_message);
+	return return_value;
+}
+
+Array Performance::get_custom_monitor_names() {
+	if (!_monitor_map.size()) {
+		return Array();
+	}
+	Array return_array;
+	return_array.resize(_monitor_map.size());
+	int index = 0;
+	for (OrderedHashMap<StringName, MonitorCall>::Element i = _monitor_map.front(); i; i = i.next()) {
+		return_array.set(index, i.key());
+		index++;
+	}
+	return return_array;
+}
+
+uint64_t Performance::get_monitor_modification_time() {
+	return _monitor_modification_time;
+}
+
 Performance::Performance() {
 	_process_time = 0;
 	_physics_process_time = 0;
+	_monitor_modification_time = 0;
 	singleton = this;
 }
+
+Performance::MonitorCall::MonitorCall(Callable p_callable, Vector<Variant> p_arguments) {
+	_callable = p_callable;
+	_arguments = p_arguments;
+}
+
+Performance::MonitorCall::MonitorCall() {
+}
+
+Variant Performance::MonitorCall::call(bool &r_error, String &r_error_message) {
+	Vector<const Variant *> arguments_mem;
+	arguments_mem.resize(_arguments.size());
+	for (int i = 0; i < _arguments.size(); i++) {
+		arguments_mem.write[i] = &_arguments[i];
+	}
+	const Variant **args = (const Variant **)arguments_mem.ptr();
+	int argc = _arguments.size();
+	Variant return_value;
+	Callable::CallError error;
+	_callable.call(args, argc, return_value, error);
+	r_error = (error.error != Callable::CallError::CALL_OK);
+	if (r_error) {
+		r_error_message = Variant::get_callable_error_text(_callable, args, argc, error);
+	}
+	return return_value;
+}
diff --git a/main/performance.h b/main/performance.h
index ddbe45fa00..5f88a24c0f 100644
--- a/main/performance.h
+++ b/main/performance.h
@@ -32,6 +32,7 @@
 #define PERFORMANCE_H
 
 #include "core/object.h"
+#include "core/ordered_hash_map.h"
 
 #define PERF_WARN_OFFLINE_FUNCTION
 #define PERF_WARN_PROCESS_SYNC
@@ -47,6 +48,19 @@ class Performance : public Object {
 	float _process_time;
 	float _physics_process_time;
 
+	class MonitorCall {
+		Callable _callable;
+		Vector<Variant> _arguments;
+
+	public:
+		MonitorCall(Callable p_callable, Vector<Variant> p_arguments);
+		MonitorCall();
+		Variant call(bool &r_error, String &r_error_message);
+	};
+
+	OrderedHashMap<StringName, MonitorCall> _monitor_map;
+	uint64_t _monitor_modification_time;
+
 public:
 	enum Monitor {
 
@@ -95,6 +109,14 @@ public:
 	void set_process_time(float p_pt);
 	void set_physics_process_time(float p_pt);
 
+	void add_custom_monitor(const StringName &p_id, const Callable &p_callable, const Vector<Variant> &p_args);
+	void remove_custom_monitor(const StringName &p_id);
+	bool has_custom_monitor(const StringName &p_id);
+	Variant get_custom_monitor(const StringName &p_id);
+	Array get_custom_monitor_names();
+
+	uint64_t get_monitor_modification_time();
+
 	static Performance *get_singleton() { return singleton; }
 
 	Performance();