[HTML5] Better fullscreen, canvas resizing.

Three canvas resize policies:
- `None`: Godot window settings are ignored.
- `Project`: Godot handles the canvas like a native app (resizing it
  when setting the window size).
- `Adaptive`: Canvas size will always adapt to browser window size.

Use `None` if you want to control the canvas size with custom JavaScript
code.

7 files changed, 195 insertions, 107 deletions

diff --git a/misc/dist/html/full-size.html b/misc/dist/html/full-size.html
index c7e657e53d..08912ba860 100644
--- a/misc/dist/html/full-size.html
+++ b/misc/dist/html/full-size.html
@@ -161,23 +161,6 @@ $GODOT_HEAD_INCLUDE
 			}
 			requestAnimationFrame(animate);
 
-			function adjustCanvasDimensions() {
-				const scale = window.devicePixelRatio || 1;
-				if (lastWidth != window.innerWidth || lastHeight != window.innerHeight || lastScale != scale) {
-					lastScale = scale;
-					lastWidth = window.innerWidth;
-					lastHeight = window.innerHeight;
-					canvas.width = Math.floor(lastWidth * scale);
-					canvas.height = Math.floor(lastHeight * scale);
-					canvas.style.width = lastWidth + "px";
-					canvas.style.height = lastHeight + "px";
-				}
-			}
-			if (GODOT_CONFIG['canvasResizePolicy'] == 2) {
-				animationCallbacks.push(adjustCanvasDimensions);
-				adjustCanvasDimensions();
-			}
-
 			function setStatusMode(mode) {
 
 				if (statusMode === mode || !initializing)
diff --git a/platform/javascript/display_server_javascript.cpp b/platform/javascript/display_server_javascript.cpp
index 92f3152ba7..a605f22e16 100644
--- a/platform/javascript/display_server_javascript.cpp
+++ b/platform/javascript/display_server_javascript.cpp
@@ -59,34 +59,13 @@ bool DisplayServerJavaScript::is_canvas_focused() {
 }
 
 bool DisplayServerJavaScript::check_size_force_redraw() {
-	int canvas_width;
-	int canvas_height;
-	emscripten_get_canvas_element_size(DisplayServerJavaScript::canvas_id, &canvas_width, &canvas_height);
-	if (last_width != canvas_width || last_height != canvas_height) {
-		last_width = canvas_width;
-		last_height = canvas_height;
-		// Update the framebuffer size for redraw.
-		emscripten_set_canvas_element_size(DisplayServerJavaScript::canvas_id, canvas_width, canvas_height);
-		return true;
-	}
-	return false;
+	return godot_js_display_size_update() != 0;
 }
 
 Point2 DisplayServerJavaScript::compute_position_in_canvas(int p_x, int p_y) {
-	DisplayServerJavaScript *display = get_singleton();
-	int canvas_x;
-	int canvas_y;
-	godot_js_display_canvas_bounding_rect_position_get(&canvas_x, &canvas_y);
-	int canvas_width;
-	int canvas_height;
-	emscripten_get_canvas_element_size(display->canvas_id, &canvas_width, &canvas_height);
-
-	double element_width;
-	double element_height;
-	emscripten_get_element_css_size(display->canvas_id, &element_width, &element_height);
-
-	return Point2((int)(canvas_width / element_width * (p_x - canvas_x)),
-			(int)(canvas_height / element_height * (p_y - canvas_y)));
+	int point[2];
+	godot_js_display_compute_position(p_x, p_y, point, point + 1);
+	return Point2(point[0], point[1]);
 }
 
 EM_BOOL DisplayServerJavaScript::fullscreen_change_callback(int p_event_type, const EmscriptenFullscreenChangeEvent *p_event, void *p_user_data) {
@@ -704,7 +683,7 @@ DisplayServerJavaScript::DisplayServerJavaScript(const String &p_rendering_drive
 	godot_js_config_canvas_id_get(canvas_id, 256);
 
 	// Handle contextmenu, webglcontextlost
-	godot_js_display_setup_canvas();
+	godot_js_display_setup_canvas(p_resolution.x, p_resolution.y, p_mode == WINDOW_MODE_FULLSCREEN);
 
 	// Check if it's windows.
 	swap_cancel_ok = godot_js_display_is_swap_ok_cancel() == 1;
@@ -748,11 +727,6 @@ DisplayServerJavaScript::DisplayServerJavaScript(const String &p_rendering_drive
 	video_driver_index = p_video_driver;
 #endif
 
-	window_set_mode(p_mode);
-	if (godot_js_config_canvas_resize_policy_get() == 1) {
-		window_set_size(p_resolution);
-	}
-
 	EMSCRIPTEN_RESULT result;
 #define EM_CHECK(ev)                         \
 	if (result != EMSCRIPTEN_RESULT_SUCCESS) \
@@ -842,17 +816,15 @@ Point2i DisplayServerJavaScript::screen_get_position(int p_screen) const {
 }
 
 Size2i DisplayServerJavaScript::screen_get_size(int p_screen) const {
-	EmscriptenFullscreenChangeEvent ev;
-	EMSCRIPTEN_RESULT result = emscripten_get_fullscreen_status(&ev);
-	ERR_FAIL_COND_V(result != EMSCRIPTEN_RESULT_SUCCESS, Size2i());
-	double scale = godot_js_display_pixel_ratio_get();
-	return Size2i(ev.screenWidth * scale, ev.screenHeight * scale);
+	int size[2];
+	godot_js_display_screen_size_get(size, size + 1);
+	return Size2(size[0], size[1]);
 }
 
 Rect2i DisplayServerJavaScript::screen_get_usable_rect(int p_screen) const {
-	int canvas[2];
-	emscripten_get_canvas_element_size(canvas_id, canvas, canvas + 1);
-	return Rect2i(0, 0, canvas[0], canvas[1]);
+	int size[2];
+	godot_js_display_window_size_get(size, size + 1);
+	return Rect2i(0, 0, size[0], size[1]);
 }
 
 int DisplayServerJavaScript::screen_get_dpi(int p_screen) const {
@@ -942,17 +914,13 @@ Size2i DisplayServerJavaScript::window_get_min_size(WindowID p_window) const {
 }
 
 void DisplayServerJavaScript::window_set_size(const Size2i p_size, WindowID p_window) {
-	last_width = p_size.x;
-	last_height = p_size.y;
-	double scale = godot_js_display_pixel_ratio_get();
-	emscripten_set_canvas_element_size(canvas_id, p_size.x, p_size.y);
-	emscripten_set_element_css_size(canvas_id, p_size.x / scale, p_size.y / scale);
+	godot_js_display_desired_size_set(p_size.x, p_size.y);
 }
 
 Size2i DisplayServerJavaScript::window_get_size(WindowID p_window) const {
-	int canvas[2];
-	emscripten_get_canvas_element_size(canvas_id, canvas, canvas + 1);
-	return Size2(canvas[0], canvas[1]);
+	int size[2];
+	godot_js_display_window_size_get(size, size + 1);
+	return Size2i(size[0], size[1]);
 }
 
 Size2i DisplayServerJavaScript::window_get_real_size(WindowID p_window) const {
@@ -966,20 +934,13 @@ void DisplayServerJavaScript::window_set_mode(WindowMode p_mode, WindowID p_wind
 	switch (p_mode) {
 		case WINDOW_MODE_WINDOWED: {
 			if (window_mode == WINDOW_MODE_FULLSCREEN) {
-				emscripten_exit_fullscreen();
+				godot_js_display_fullscreen_exit();
 			}
 			window_mode = WINDOW_MODE_WINDOWED;
-			window_set_size(Size2i(last_width, last_height));
 		} break;
 		case WINDOW_MODE_FULLSCREEN: {
-			EmscriptenFullscreenStrategy strategy;
-			strategy.scaleMode = EMSCRIPTEN_FULLSCREEN_SCALE_STRETCH;
-			strategy.canvasResolutionScaleMode = EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_STDDEF;
-			strategy.filteringMode = EMSCRIPTEN_FULLSCREEN_FILTERING_DEFAULT;
-			strategy.canvasResizedCallback = nullptr;
-			EMSCRIPTEN_RESULT result = emscripten_request_fullscreen_strategy(canvas_id, false, &strategy);
-			ERR_FAIL_COND_MSG(result == EMSCRIPTEN_RESULT_FAILED_NOT_DEFERRED, "Enabling fullscreen is only possible from an input callback for the HTML5 platform.");
-			ERR_FAIL_COND_MSG(result != EMSCRIPTEN_RESULT_SUCCESS, "Enabling fullscreen is only possible from an input callback for the HTML5 platform.");
+			int result = godot_js_display_fullscreen_request();
+			ERR_FAIL_COND_MSG(result, "The request was denied. Remember that enabling fullscreen is only possible from an input callback for the HTML5 platform.");
 		} break;
 		case WINDOW_MODE_MAXIMIZED:
 		case WINDOW_MODE_MINIMIZED:
diff --git a/platform/javascript/display_server_javascript.h b/platform/javascript/display_server_javascript.h
index e2fe731abf..47e25ab2a0 100644
--- a/platform/javascript/display_server_javascript.h
+++ b/platform/javascript/display_server_javascript.h
@@ -57,9 +57,6 @@ private:
 	double last_click_ms = 0;
 	int last_click_button_index = -1;
 
-	int last_width = 0;
-	int last_height = 0;
-
 	bool swap_cancel_ok = false;
 
 	// utilities
diff --git a/platform/javascript/export/export.cpp b/platform/javascript/export/export.cpp
index fa8b000259..353cc49ef8 100644
--- a/platform/javascript/export/export.cpp
+++ b/platform/javascript/export/export.cpp
@@ -296,7 +296,7 @@ void EditorExportPlatformJavaScript::_fix_html(Vector<uint8_t> &p_html, const Re
 		args.push_back(flags[i]);
 	}
 	Dictionary config;
-	config["canvasResizePolicy"] = p_preset->get("html/full_window_size") ? 2 : 1;
+	config["canvasResizePolicy"] = p_preset->get("html/canvas_resize_policy");
 	config["gdnativeLibs"] = libs;
 	config["executable"] = p_name;
 	config["args"] = args;
@@ -350,7 +350,7 @@ void EditorExportPlatformJavaScript::get_export_options(List<ExportOption> *r_op
 
 	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "html/custom_html_shell", PROPERTY_HINT_FILE, "*.html"), ""));
 	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "html/head_include", PROPERTY_HINT_MULTILINE_TEXT), ""));
-	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "html/full_window_size"), true));
+	r_options->push_back(ExportOption(PropertyInfo(Variant::INT, "html/canvas_resize_policy", PROPERTY_HINT_ENUM, "None,Project,Adaptive"), 2));
 }
 
 String EditorExportPlatformJavaScript::get_name() const {
diff --git a/platform/javascript/godot_js.h b/platform/javascript/godot_js.h
index 81443de7a2..5aa8677a54 100644
--- a/platform/javascript/godot_js.h
+++ b/platform/javascript/godot_js.h
@@ -40,7 +40,6 @@ extern "C" {
 // Config
 extern void godot_js_config_locale_get(char *p_ptr, int p_ptr_max);
 extern void godot_js_config_canvas_id_get(char *p_ptr, int p_ptr_max);
-extern int godot_js_config_canvas_resize_policy_get();
 
 // OS
 extern void godot_js_os_finish_async(void (*p_callback)());
@@ -61,10 +60,15 @@ extern int godot_js_display_is_swap_ok_cancel();
 // Display canvas
 extern void godot_js_display_canvas_focus();
 extern int godot_js_display_canvas_is_focused();
-extern void godot_js_display_canvas_bounding_rect_position_get(int32_t *p_x, int32_t *p_y);
 
 // Display window
-extern void godot_js_display_window_request_fullscreen();
+extern void godot_js_display_desired_size_set(int p_width, int p_height);
+extern int godot_js_display_size_update();
+extern void godot_js_display_window_size_get(int32_t *p_x, int32_t *p_y);
+extern void godot_js_display_screen_size_get(int32_t *p_x, int32_t *p_y);
+extern int godot_js_display_fullscreen_request();
+extern int godot_js_display_fullscreen_exit();
+extern void godot_js_display_compute_position(int p_x, int p_y, int32_t *r_x, int32_t *r_y);
 extern void godot_js_display_window_title_set(const char *p_text);
 extern void godot_js_display_window_icon_set(const uint8_t *p_ptr, int p_len);
 
@@ -88,7 +92,7 @@ extern int godot_js_display_gamepad_sample_get(int p_idx, float r_btns[16], int3
 extern void godot_js_display_notification_cb(void (*p_callback)(int p_notification), int p_enter, int p_exit, int p_in, int p_out);
 extern void godot_js_display_paste_cb(void (*p_callback)(const char *p_text));
 extern void godot_js_display_drop_files_cb(void (*p_callback)(char **p_filev, int p_filec));
-extern void godot_js_display_setup_canvas();
+extern void godot_js_display_setup_canvas(int p_width, int p_height, int p_fullscreen);
 #ifdef __cplusplus
 }
 #endif
diff --git a/platform/javascript/js/libs/library_godot_display.js b/platform/javascript/js/libs/library_godot_display.js
index 9ec295b39f..fdb5cc0ec2 100644
--- a/platform/javascript/js/libs/library_godot_display.js
+++ b/platform/javascript/js/libs/library_godot_display.js
@@ -396,13 +396,118 @@ const GodotDisplayGamepads = {
 };
 mergeInto(LibraryManager.library, GodotDisplayGamepads);
 
+const GodotDisplayScreen = {
+	$GodotDisplayScreen__deps: ['$GodotConfig', '$GodotOS', '$GL', 'emscripten_webgl_get_current_context'],
+	$GodotDisplayScreen: {
+		desired_size: [0, 0],
+		isFullscreen: function () {
+			const elem = document.fullscreenElement || document.mozFullscreenElement
+				|| document.webkitFullscreenElement || document.msFullscreenElement;
+			if (elem) {
+				return elem === GodotConfig.canvas;
+			}
+			// But maybe knowing the element is not supported.
+			return document.fullscreen || document.mozFullScreen
+				|| document.webkitIsFullscreen;
+		},
+		hasFullscreen: function () {
+			return document.fullscreenEnabled || document.mozFullScreenEnabled
+				|| document.webkitFullscreenEnabled;
+		},
+		requestFullscreen: function () {
+			if (!GodotDisplayScreen.hasFullscreen()) {
+				return 1;
+			}
+			const canvas = GodotConfig.canvas;
+			try {
+				const promise = (canvas.requestFullscreen || canvas.msRequestFullscreen
+					|| canvas.mozRequestFullScreen || canvas.mozRequestFullscreen
+					|| canvas.webkitRequestFullscreen
+				).call(canvas);
+				// Some browsers (Safari) return undefined.
+				// For the standard ones, we need to catch it.
+				if (promise) {
+					promise.catch(function () {
+						// nothing to do.
+					});
+				}
+			} catch (e) {
+				return 1;
+			}
+			return 0;
+		},
+		exitFullscreen: function () {
+			if (!GodotDisplayScreen.isFullscreen()) {
+				return 0;
+			}
+			try {
+				const promise = document.exitFullscreen();
+				if (promise) {
+					promise.catch(function () {
+						// nothing to do.
+					});
+				}
+			} catch (e) {
+				return 1;
+			}
+			return 0;
+		},
+		_updateGL: function () {
+			const gl_context_handle = _emscripten_webgl_get_current_context(); // eslint-disable-line no-undef
+			const gl = GL.getContext(gl_context_handle);
+			if (gl) {
+				GL.resizeOffscreenFramebuffer(gl);
+			}
+		},
+		updateSize: function () {
+			const isFullscreen = GodotDisplayScreen.isFullscreen();
+			const wantsFullWindow = GodotConfig.canvas_resize_policy === 2;
+			const noResize = GodotConfig.canvas_resize_policy === 0;
+			const wwidth = GodotDisplayScreen.desired_size[0];
+			const wheight = GodotDisplayScreen.desired_size[1];
+			const canvas = GodotConfig.canvas;
+			let width = wwidth;
+			let height = wheight;
+			if (noResize) {
+				// Don't resize canvas, just update GL if needed.
+				if (canvas.width !== width || canvas.height !== height) {
+					GodotDisplayScreen.desired_size = [canvas.width, canvas.height];
+					GodotDisplayScreen._updateGL();
+					return 1;
+				}
+				return 0;
+			}
+			const scale = window.devicePixelRatio || 1;
+			if (isFullscreen || wantsFullWindow) {
+				// We need to match screen size.
+				width = window.innerWidth * scale;
+				height = window.innerHeight * scale;
+			}
+			const csw = `${width / scale}px`;
+			const csh = `${height / scale}px`;
+			if (canvas.style.width !== csw || canvas.style.height !== csh || canvas.width !== width || canvas.height !== height) {
+				// Size doesn't match.
+				// Resize canvas, set correct CSS pixel size, update GL.
+				canvas.width = width;
+				canvas.height = height;
+				canvas.style.width = csw;
+				canvas.style.height = csh;
+				GodotDisplayScreen._updateGL();
+				return 1;
+			}
+			return 0;
+		},
+	},
+};
+mergeInto(LibraryManager.library, GodotDisplayScreen);
+
 /**
  * Display server interface.
  *
  * Exposes all the functions needed by DisplayServer implementation.
  */
 const GodotDisplay = {
-	$GodotDisplay__deps: ['$GodotConfig', '$GodotRuntime', '$GodotDisplayCursor', '$GodotDisplayListeners', '$GodotDisplayDragDrop', '$GodotDisplayGamepads'],
+	$GodotDisplay__deps: ['$GodotConfig', '$GodotRuntime', '$GodotDisplayCursor', '$GodotDisplayListeners', '$GodotDisplayDragDrop', '$GodotDisplayGamepads', '$GodotDisplayScreen'],
 	$GodotDisplay: {
 		window_icon: '',
 		findDPI: function () {
@@ -453,6 +558,48 @@ const GodotDisplay = {
 		return window.devicePixelRatio || 1;
 	},
 
+	godot_js_display_fullscreen_request__sig: 'i',
+	godot_js_display_fullscreen_request: function () {
+		return GodotDisplayScreen.requestFullscreen();
+	},
+
+	godot_js_display_fullscreen_exit__sig: 'i',
+	godot_js_display_fullscreen_exit: function () {
+		return GodotDisplayScreen.exitFullscreen();
+	},
+
+	godot_js_display_desired_size_set__sig: 'v',
+	godot_js_display_desired_size_set: function (width, height) {
+		GodotDisplayScreen.desired_size = [width, height];
+		GodotDisplayScreen.updateSize();
+	},
+
+	godot_js_display_size_update__sig: 'i',
+	godot_js_display_size_update: function () {
+		return GodotDisplayScreen.updateSize();
+	},
+
+	godot_js_display_screen_size_get__sig: 'vii',
+	godot_js_display_screen_size_get: function (width, height) {
+		const scale = window.devicePixelRatio || 1;
+		GodotRuntime.setHeapValue(width, window.screen.width * scale, 'i32');
+		GodotRuntime.setHeapValue(height, window.screen.height * scale, 'i32');
+	},
+
+	godot_js_display_window_size_get: function (p_width, p_height) {
+		GodotRuntime.setHeapValue(p_width, GodotConfig.canvas.width, 'i32');
+		GodotRuntime.setHeapValue(p_height, GodotConfig.canvas.height, 'i32');
+	},
+
+	godot_js_display_compute_position: function (x, y, r_x, r_y) {
+		const canvas = GodotConfig.canvas;
+		const rect = canvas.getBoundingClientRect();
+		const rw = canvas.width / rect.width;
+		const rh = canvas.height / rect.height;
+		GodotRuntime.setHeapValue(r_x, (x - rect.x) * rw, 'i32');
+		GodotRuntime.setHeapValue(r_y, (y - rect.y) * rh, 'i32');
+	},
+
 	/*
 	 * Canvas
 	 */
@@ -466,13 +613,6 @@ const GodotDisplay = {
 		return document.activeElement === GodotConfig.canvas;
 	},
 
-	godot_js_display_canvas_bounding_rect_position_get__sig: 'vii',
-	godot_js_display_canvas_bounding_rect_position_get: function (r_x, r_y) {
-		const brect = GodotConfig.canvas.getBoundingClientRect();
-		GodotRuntime.setHeapValue(r_x, brect.x, 'i32');
-		GodotRuntime.setHeapValue(r_y, brect.y, 'i32');
-	},
-
 	/*
 	 * Touchscreen
 	 */
@@ -516,15 +656,6 @@ const GodotDisplay = {
 	/*
 	 * Window
 	 */
-	godot_js_display_window_request_fullscreen__sig: 'v',
-	godot_js_display_window_request_fullscreen: function () {
-		const canvas = GodotConfig.canvas;
-		(canvas.requestFullscreen || canvas.msRequestFullscreen
-			|| canvas.mozRequestFullScreen || canvas.mozRequestFullscreen
-			|| canvas.webkitRequestFullscreen
-		).call(canvas);
-	},
-
 	godot_js_display_window_title_set__sig: 'vi',
 	godot_js_display_window_title_set: function (p_data) {
 		document.title = GodotRuntime.parseString(p_data);
@@ -645,8 +776,8 @@ const GodotDisplay = {
 		GodotDisplayListeners.add(canvas, 'drop', GodotDisplayDragDrop.handler(dropFiles));
 	},
 
-	godot_js_display_setup_canvas__sig: 'v',
-	godot_js_display_setup_canvas: function () {
+	godot_js_display_setup_canvas__sig: 'viii',
+	godot_js_display_setup_canvas: function (p_width, p_height, p_fullscreen) {
 		const canvas = GodotConfig.canvas;
 		GodotDisplayListeners.add(canvas, 'contextmenu', function (ev) {
 			ev.preventDefault();
@@ -655,6 +786,23 @@ const GodotDisplay = {
 			alert('WebGL context lost, please reload the page'); // eslint-disable-line no-alert
 			ev.preventDefault();
 		}, false);
+		switch (GodotConfig.canvas_resize_policy) {
+		case 0: // None
+			GodotDisplayScreen.desired_size = [canvas.width, canvas.height];
+			break;
+		case 1: // Project
+			GodotDisplayScreen.desired_size = [p_width, p_height];
+			break;
+		default: // Full window
+			// Ensure we display in the right place, the size will be handled by updateSize
+			canvas.style.position = 'absolute';
+			canvas.style.top = 0;
+			canvas.style.left = 0;
+			break;
+		}
+		if (p_fullscreen) {
+			GodotDisplayScreen.requestFullscreen();
+		}
 	},
 
 	/*
diff --git a/platform/javascript/js/libs/library_godot_os.js b/platform/javascript/js/libs/library_godot_os.js
index ef6df17e97..0f189b013c 100644
--- a/platform/javascript/js/libs/library_godot_os.js
+++ b/platform/javascript/js/libs/library_godot_os.js
@@ -91,11 +91,6 @@ const GodotConfig = {
 	godot_js_config_locale_get: function (p_ptr, p_ptr_max) {
 		GodotRuntime.stringToHeap(GodotConfig.locale, p_ptr, p_ptr_max);
 	},
-
-	godot_js_config_canvas_resize_policy_get__sig: 'i',
-	godot_js_config_canvas_resize_policy_get: function () {
-		return GodotConfig.canvas_resize_policy;
-	},
 };
 
 autoAddDeps(GodotConfig, '$GodotConfig');