Add support for setting page zoom

Previously, the only way to scale up a page was to use custom CSS,
which may or may not work well depending on how the CSS rules of the
page being displayed were written, or to transform the browser source,
which would be blurry.

To make it possible to do this properly, I've implemented support for
setting the zoom level of the browser, equivalent to pressing Ctrl-+ /
Ctrl-- in a browser.

The range of [-6, 9] comes from kPresetZoomFactorsArray in Chromium.
Zoom levels are indexes into this array, offset so that a 0 zoom level
is 1.0.

browser-client.cpp

@@ -648,6 +648,12 @@ void BrowserClient::OnAudioStreamStopped(CefRefPtr<CefBrowser> browser, int id)
 }
 #endif
 
+void BrowserClient::OnLoadStart(CefRefPtr<CefBrowser> browser,
+				CefRefPtr<CefFrame>, TransitionType)
+{
+	browser->GetHost()->SetZoomLevel(bs->zoom);
+}
+
 void BrowserClient::OnLoadEnd(CefRefPtr<CefBrowser>, CefRefPtr<CefFrame> frame,
 			      int)
 {

browser-client.hpp

@@ -179,6 +179,10 @@ class BrowserClient : public CefClient,
 					  int frames_per_buffer) override;
 #endif
 	/* CefLoadHandler */
+	virtual void OnLoadStart(CefRefPtr<CefBrowser> browser,
+				 CefRefPtr<CefFrame> frame,
+				 TransitionType transition_type) override;
+
 	virtual void OnLoadEnd(CefRefPtr<CefBrowser> browser,
 			       CefRefPtr<CefFrame> frame,
 			       int httpStatusCode) override;

obs-browser-plugin.cpp

@@ -187,6 +187,8 @@ static obs_properties_t *browser_source_get_properties(void *data)
 			       8192, 1);
 	obs_properties_add_int(props, "height", obs_module_text("Height"), 1,
 			       8192, 1);
+	obs_properties_add_int(props, "zoom", obs_module_text("Zoom"), -6, 9,
+			       1);
 
 	obs_properties_add_bool(props, "reroute_audio",
 				obs_module_text("RerouteAudio"));

obs-browser-source.cpp

@@ -512,6 +512,7 @@ void BrowserSource::Update(obs_data_t *settings)
 		bool n_is_local;
 		int n_width;
 		int n_height;
+		int n_zoom;
 		bool n_fps_custom;
 		int n_fps;
 		bool n_shutdown;
@@ -524,6 +525,7 @@ void BrowserSource::Update(obs_data_t *settings)
 		n_is_local = obs_data_get_bool(settings, "is_local_file");
 		n_width = (int)obs_data_get_int(settings, "width");
 		n_height = (int)obs_data_get_int(settings, "height");
+		n_zoom = (int)obs_data_get_int(settings, "zoom");
 		n_fps_custom = obs_data_get_bool(settings, "fps_custom");
 		n_fps = (int)obs_data_get_int(settings, "fps");
 		n_shutdown = obs_data_get_bool(settings, "shutdown");
@@ -582,11 +584,13 @@ void BrowserSource::Update(obs_data_t *settings)
 		    n_reroute == reroute_audio &&
 		    n_webpage_control_level == webpage_control_level) {
 
-			if (n_width == width && n_height == height)
+			if (n_width == width && n_height == height &&
+			    n_zoom == zoom)
 				return;
 
 			width = n_width;
 			height = n_height;
+			zoom = n_zoom;
 			ExecuteOnBrowser(
 				[=](CefRefPtr<CefBrowser> cefBrowser) {
 					const CefSize cefSize(width, height);
@@ -596,6 +600,8 @@ void BrowserSource::Update(obs_data_t *settings)
 						->OnAutoResize(cefBrowser,
 							       cefSize);
 					cefBrowser->GetHost()->WasResized();
+					cefBrowser->GetHost()->SetZoomLevel(
+						zoom);
 					cefBrowser->GetHost()->Invalidate(
 						PET_VIEW);
 				},
@@ -606,6 +612,7 @@ void BrowserSource::Update(obs_data_t *settings)
 		is_local = n_is_local;
 		width = n_width;
 		height = n_height;
+		zoom = n_zoom;
 		fps = n_fps;
 		fps_custom = n_fps_custom;
 		shutdown_on_invisible = n_shutdown;

obs-browser-source.hpp

@@ -81,6 +81,7 @@ struct BrowserSource {
 
 	int width = 0;
 	int height = 0;
+	int zoom = 0;
 	bool fps_custom = false;
 	int fps = 0;
 	double canvas_fps = 0;