add transparency

CMakeLists.txt

@@ -10,7 +10,7 @@ pkg_check_modules(OBS REQUIRED IMPORTED_TARGET libobs)
 pkg_check_modules(GLIB REQUIRED IMPORTED_TARGET glib-2.0)
 pkg_check_modules(GTK REQUIRED IMPORTED_TARGET gtk+-3.0)
 pkg_check_modules(WEBKIT REQUIRED IMPORTED_TARGET webkit2gtk-4.1)
-pkg_check_modules(X11_CAPTURE REQUIRED IMPORTED_TARGET x11 xcomposite xext)
+pkg_check_modules(X11_CAPTURE REQUIRED IMPORTED_TARGET x11 xcomposite xdamage xext)
 
 add_library(obs-webkit-browser MODULE
   src/plugin.c

README.md

@@ -14,6 +14,7 @@ WebKitGTK 4.1 в отдельном процессе на приватном Xvf
   при этом Xvfb используется только как изолированный невидимый дисплей;
 - прямой XShm-захват итогового кадра Xvfb для непрозрачных страниц и
   XComposite/XShm-захват с alpha для прозрачных;
+- XDamage-пропуск чтения framebuffer, пока содержимое страницы не меняется;
 - shared-memory транспорт кадров без многомегабайтной записи в pipe;
 - мышь, прокрутка, фокус и базовый ввод с клавиатуры через окно Interact OBS;
 - перезагрузка страницы и остановка renderer-процесса у скрытого source.

scripts/install-deps-alpine.sh

@@ -17,5 +17,5 @@ $ROOT apk add \
 	obs-studio obs-studio-dev \
 	gtk+3.0 gtk+3.0-dev \
 	webkit2gtk-4.1 webkit2gtk-4.1-dev \
-	libx11-dev libxcomposite-dev libxext-dev \
+	libx11-dev libxcomposite-dev libxdamage-dev libxext-dev \
 	xvfb mesa-dri-gallium

src/renderer.c

@@ -6,6 +6,7 @@
 #include <X11/Xutil.h>
 #include <X11/extensions/XShm.h>
 #include <X11/extensions/Xcomposite.h>
+#include <X11/extensions/Xdamage.h>
 
 #include <errno.h>
 #include <fcntl.h>
@@ -52,6 +53,8 @@ struct renderer {
 	Display *capture_display;
 	Window capture_window;
 	Pixmap capture_pixmap;
+	Damage capture_damage;
+	int damage_event_base;
 	XImage *capture_image;
 	XShmSegmentInfo capture_shm;
 	bool capture_redirected;
@@ -199,6 +202,10 @@ static bool initialize_x11_capture(struct renderer *renderer)
 	renderer->capture_display = XOpenDisplay(NULL);
 	if (!renderer->capture_display || !XShmQueryExtension(renderer->capture_display))
 		return false;
+	int damage_error_base = 0;
+	if (!XDamageQueryExtension(renderer->capture_display, &renderer->damage_event_base,
+				   &damage_error_base))
+		return false;
 
 	/* An opaque WebKit view may render into child/compositor surfaces which are
 	 * absent from the top-level window's named backing pixmap.  Xvfb's root
@@ -224,6 +231,10 @@ static bool initialize_x11_capture(struct renderer *renderer)
 		if (!renderer->capture_pixmap)
 			return false;
 	}
+	renderer->capture_damage = XDamageCreate(renderer->capture_display,
+					 renderer->capture_window, XDamageReportNonEmpty);
+	if (!renderer->capture_damage)
+		return false;
 	XWindowAttributes attributes;
 	if (!XGetWindowAttributes(renderer->capture_display, renderer->capture_window, &attributes))
 		return false;
@@ -257,6 +268,8 @@ static bool initialize_x11_capture(struct renderer *renderer)
 
 static void destroy_x11_capture(struct renderer *renderer)
 {
+	if (renderer->capture_damage)
+		XDamageDestroy(renderer->capture_display, renderer->capture_damage);
 	if (renderer->capture_attached) {
 		XShmDetach(renderer->capture_display, &renderer->capture_shm);
 		XSync(renderer->capture_display, False);
@@ -288,11 +301,28 @@ static void publish_frame(struct renderer *renderer, const uint8_t *pixels, int
 	for (uint32_t y = 0; y < renderer->config.height; y++)
 		memcpy(destination + (size_t)y * renderer->config.width * 4,
 		       pixels + (size_t)y * (size_t)stride, (size_t)renderer->config.width * 4);
+	size_t size = owb_frame_size(renderer->config.width, renderer->config.height);
+	for (size_t offset = 0; offset < size; offset += 4) {
+		uint8_t *pixel = destination + offset;
 		if (!preserve_alpha) {
-		for (size_t offset = 3, size = owb_frame_size(renderer->config.width,
+			pixel[3] = 255;
-							      renderer->config.height);
+			continue;
-		     offset < size; offset += 4)
+		}
-			destination[offset] = 255;
+
+		/* XComposite ARGB pixmaps contain premultiplied color channels, while
+		 * OBS treats an asynchronous VIDEO_FORMAT_BGRA frame as straight alpha.
+		 * Passing the pixmap through unchanged multiplies translucent colors a
+		 * second time during scene compositing and leaves black fringes. */
+		unsigned alpha = pixel[3];
+		if (alpha == 0) {
+			pixel[0] = pixel[1] = pixel[2] = 0;
+		} else if (alpha < 255) {
+			for (size_t channel = 0; channel < 3; channel++) {
+				unsigned straight = ((unsigned)pixel[channel] * 255u + alpha / 2u) /
+						    alpha;
+				pixel[channel] = (uint8_t)(straight > 255u ? 255u : straight);
+			}
+		}
 	}
 	__atomic_store_n(&renderer->shared->sequence[slot], complete_sequence, __ATOMIC_RELEASE);
 	uint8_t notification = (uint8_t)slot;
@@ -310,6 +340,18 @@ static void publish_x11_frame(struct renderer *renderer)
 		      renderer->config.transparent && renderer->capture_image->depth == 32);
 }
 
+static bool capture_was_damaged(struct renderer *renderer)
+{
+	bool damaged = false;
+	while (XPending(renderer->capture_display)) {
+		XEvent event;
+		XNextEvent(renderer->capture_display, &event);
+		if (event.type == renderer->damage_event_base + XDamageNotify)
+			damaged = true;
+	}
+	return damaged;
+}
+
 static void advance_deadline(struct timespec *deadline, long interval_ns)
 {
 	deadline->tv_nsec += interval_ns;
@@ -325,8 +367,17 @@ static void *capture_loop(void *opaque)
 	long interval_ns = 1000000000L / (long)renderer->config.fps;
 	struct timespec deadline;
 	clock_gettime(CLOCK_MONOTONIC, &deadline);
+	bool first_frame = true;
 	while (!atomic_load_explicit(&renderer->stopping, memory_order_acquire)) {
+		bool damaged = capture_was_damaged(renderer);
+		if (first_frame || damaged) {
+			/* Clear the accumulated region before capture. Changes arriving while
+			 * XShmGetImage runs then produce a fresh notification for the next tick. */
+			XDamageSubtract(renderer->capture_display, renderer->capture_damage,
+					None, None);
 			publish_x11_frame(renderer);
+			first_frame = false;
+		}
 		advance_deadline(&deadline, interval_ns);
 		while (clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &deadline, NULL) == EINTR) {
 		}
@@ -548,6 +599,15 @@ int main(void)
 		NULL, NULL);
 	webkit_user_content_manager_add_script(manager, reporter);
 	webkit_user_script_unref(reporter);
+	if (renderer.config.transparent) {
+		static const char transparent_page_css[] =
+			"html,body{background:transparent!important}";
+		WebKitUserStyleSheet *transparent_sheet = webkit_user_style_sheet_new(
+			transparent_page_css, WEBKIT_USER_CONTENT_INJECT_ALL_FRAMES,
+			WEBKIT_USER_STYLE_LEVEL_USER, NULL, NULL);
+		webkit_user_content_manager_add_style_sheet(manager, transparent_sheet);
+		webkit_user_style_sheet_unref(transparent_sheet);
+	}
 	if (*renderer.config.css) {
 		WebKitUserStyleSheet *sheet = webkit_user_style_sheet_new(renderer.config.css,
 			WEBKIT_USER_CONTENT_INJECT_ALL_FRAMES, WEBKIT_USER_STYLE_LEVEL_USER, NULL, NULL);
@@ -600,7 +660,7 @@ int main(void)
 	while (gtk_events_pending())
 		gtk_main_iteration();
 	if (!initialize_x11_capture(&renderer)) {
-		fprintf(stderr, "Cannot initialize XComposite/XShm capture\n");
+		fprintf(stderr, "Cannot initialize XComposite/XDamage/XShm capture\n");
 		return 6;
 	}
 

tests/renderer-smoke-test.c

@@ -101,9 +101,10 @@ int main(int argc, char **argv)
 		return 2;
 	}
 
-	const char internal_url[] = "data:text/html,<body><div id='box'></div></body>";
+	const char internal_url[] =
-	const char transparent_css[] = "html,body{margin:0;background:transparent!important}"
+		"data:text/html,<body style='background:rgb(3,5,7)'><div id='box'></div></body>";
-				       "#box{position:fixed;inset:0;background:rgba(255,0,0,.5)}";
+	const char transparent_css[] = "html,body{margin:0}"
+				       "#box{position:fixed;inset:16px;background:rgba(255,0,0,.5)}";
 	const char opaque_css[] = "html,body{margin:0;background:rgb(7,19,31)!important}"
 				  "#box{position:fixed;left:16px;top:16px;width:32px;height:32px;"
 				  "background:rgb(241,23,17);transform:translateZ(0);filter:blur(.1px)}";
@@ -125,6 +126,7 @@ int main(int argc, char **argv)
 		    write_exact(control[0], url, strlen(url)) &&
 		    write_exact(control[0], css, strlen(css));
 	uint8_t last_bgra[4] = {0};
+	uint8_t last_corner_bgra[4] = {0};
 	bool found_red = false;
 	int max_attempts = external_url ? 120 : 60;
 	for (int attempt = 0; sent && attempt < max_attempts; attempt++) {
@@ -158,11 +160,14 @@ int main(int argc, char **argv)
 		}
 		size_t center = ((size_t)(height / 2) * width + width / 2) * 4;
 		memcpy(last_bgra, frame + center, sizeof(last_bgra));
+		memcpy(last_corner_bgra, frame, sizeof(last_corner_bgra));
 		bool expected = opaque
 			? last_bgra[0] < 32 && last_bgra[1] < 40 && last_bgra[2] > 210 &&
 				  last_bgra[3] == 255
-			: last_bgra[0] < 8 && last_bgra[1] < 8 && last_bgra[2] > 120 &&
+			: last_bgra[0] < 8 && last_bgra[1] < 8 && last_bgra[2] > 248 &&
-				  last_bgra[2] < 136 && last_bgra[3] > 120 && last_bgra[3] < 136;
+				  last_bgra[3] > 120 && last_bgra[3] < 136 &&
+				  last_corner_bgra[0] == 0 && last_corner_bgra[1] == 0 &&
+				  last_corner_bgra[2] == 0 && last_corner_bgra[3] == 0;
 		if (expected) {
 			found_red = true;
 			break;
@@ -183,9 +188,10 @@ int main(int argc, char **argv)
 		}
 		fprintf(stderr,
 			"renderer did not produce the expected %s red BGRA frame "
-			"(center BGRA=%u,%u,%u,%u)\n",
+			"(center BGRA=%u,%u,%u,%u; corner BGRA=%u,%u,%u,%u)\n",
 			opaque ? "opaque" : "transparent", last_bgra[0], last_bgra[1],
-			last_bgra[2], last_bgra[3]);
+			last_bgra[2], last_bgra[3], last_corner_bgra[0], last_corner_bgra[1],
+			last_corner_bgra[2], last_corner_bgra[3]);
 		return 1;
 	}
 	return 0;