2 frames 2 pacing

src/backend/backend.c

@@ -82,13 +82,17 @@
 }
 
 /// paint all windows
-void paint_all_new(session_t *ps, struct managed_win *t) {
+///
+/// Returns if any render command is issued. IOW if nothing on the screen has changed,
+/// this function will return false.
+bool paint_all_new(session_t *ps, struct managed_win *const t) {
 	struct timespec now = get_time_timespec();
 	auto paint_all_start_us =
 	    (uint64_t)now.tv_sec * 1000000UL + (uint64_t)now.tv_nsec / 1000;
 	if (ps->backend_data->ops->device_status &&
 	    ps->backend_data->ops->device_status(ps->backend_data) != DEVICE_STATUS_NORMAL) {
-		return handle_device_reset(ps);
+		handle_device_reset(ps);
+		return false;
 	}
 	if (ps->o.xrender_sync_fence) {
 		if (ps->xsync_exists && !x_fence_sync(&ps->c, ps->sync_fence)) {
@@ -114,7 +118,7 @@
 
 	if (!pixman_region32_not_empty(&reg_damage)) {
 		pixman_region32_fini(&reg_damage);
-		return;
+		return false;
 	}
 
 #ifdef DEBUG_REPAINT
@@ -190,16 +194,15 @@
 	auto after_damage_us = (uint64_t)now.tv_sec * 1000000UL + (uint64_t)now.tv_nsec / 1000;
 	log_trace("Getting damage took %" PRIu64 " us", after_damage_us - after_sync_fence_us);
 	if (ps->next_render > 0) {
-		log_trace("Render schedule deviation: %ld us (%s) %" PRIu64 " %ld",
-		          labs((long)after_damage_us - (long)ps->next_render),
-		          after_damage_us < ps->next_render ? "early" : "late",
-		          after_damage_us, ps->next_render);
+		log_verbose("Render schedule deviation: %ld us (%s) %" PRIu64 " %ld",
+		            labs((long)after_damage_us - (long)ps->next_render),
+		            after_damage_us < ps->next_render ? "early" : "late",
+		            after_damage_us, ps->next_render);
 		ps->last_schedule_delay = 0;
 		if (after_damage_us > ps->next_render) {
 			ps->last_schedule_delay = after_damage_us - ps->next_render;
 		}
 	}
-	ps->did_render = true;
 
 	if (ps->backend_data->ops->prepare) {
 		ps->backend_data->ops->prepare(ps->backend_data, &reg_paint);
@@ -219,7 +222,7 @@
 	// on top of that window. This is used to reduce the number of pixels painted.
 	//
 	// Whether this is beneficial is to be determined XXX
-	for (auto w = t; w; w = w->prev_trans) {
+	for (struct managed_win *w = t; w; w = w->prev_trans) {
 		pixman_region32_subtract(&reg_visible, &ps->screen_reg, w->reg_ignore);
 		assert(!(w->flags & WIN_FLAGS_IMAGE_ERROR));
 		assert(!(w->flags & WIN_FLAGS_PIXMAP_STALE));
@@ -541,6 +544,7 @@
 	for (win *w = t; w; w = w->prev_trans)
 		log_trace(" %#010lx", w->id);
 #endif
+	return true;
 }
 
 // vim: set noet sw=8 ts=8 :

src/backend/backend.h

@@ -366,4 +366,8 @@ struct backend_operations {
 
 extern struct backend_operations *backend_list[];
 
-void paint_all_new(session_t *ps, struct managed_win *const t) attr_nonnull(1);
+/// paint all windows
+///
+/// Returns if any render command is issued. IOW if nothing on the screen has changed,
+/// this function will return false.
+bool paint_all_new(session_t *ps, struct managed_win *t) attr_nonnull(1);

src/backend/driver.c

@@ -19,6 +19,13 @@
 	}
 }
 
+enum vblank_scheduler_type choose_vblank_scheduler(enum driver driver) {
+	if (driver & DRIVER_NVIDIA) {
+		return VBLANK_SCHEDULER_SGI_VIDEO_SYNC;
+	}
+	return VBLANK_SCHEDULER_PRESENT;
+}
+
 enum driver detect_driver(xcb_connection_t *c, backend_t *backend_data, xcb_window_t window) {
 	enum driver ret = 0;
 	// First we try doing backend agnostic detection using RANDR

src/backend/driver.h

@@ -7,6 +7,7 @@
 #include <stdio.h>
 #include <xcb/xcb.h>
 
+#include "config.h"
 #include "utils.h"
 
 struct session;
@@ -41,6 +42,8 @@ enum driver detect_driver(xcb_connection_t *, struct backend_base *, xcb_window_
 
 /// Apply driver specified global workarounds. It's safe to call this multiple times.
 void apply_driver_workarounds(struct session *ps, enum driver);
+/// Choose a vblank scheduler based on the driver.
+enum vblank_scheduler_type choose_vblank_scheduler(enum driver driver);
 
 // Print driver names to stdout, for diagnostics
 static inline void print_drivers(enum driver drivers) {

src/common.h

@@ -139,8 +139,6 @@ typedef struct session {
 	// === Event handlers ===
 	/// ev_io for X connection
 	ev_io xiow;
-	/// Timer for checking DPMS power level
-	ev_timer dpms_check_timer;
 	/// Timeout for delayed unredirection.
 	ev_timer unredir_timer;
 	/// Timer for fading
@@ -214,26 +212,19 @@ typedef struct session {
 	bool first_frame;
 	/// Whether screen has been turned off
 	bool screen_is_off;
-	/// Event context for X Present extension.
-	uint32_t present_event_id;
-	xcb_special_event_t *present_event;
 	/// When last MSC event happened, in useconds.
 	uint64_t last_msc_instant;
 	/// The last MSC number
 	uint64_t last_msc;
-	/// When the currently rendered frame will be displayed.
-	/// 0 means there is no pending frame.
-	uint64_t target_msc;
 	/// The delay between when the last frame was scheduled to be rendered, and when
 	/// the render actually started.
 	uint64_t last_schedule_delay;
 	/// When do we want our next frame to start rendering.
 	uint64_t next_render;
-	/// Did we actually render the last frame. Sometimes redraw will be scheduled only
-	/// to find out nothing has changed. In which case this will be set to false.
-	bool did_render;
 	/// Whether we can perform frame pacing.
 	bool frame_pacing;
+	/// Vblank event scheduler
+	struct vblank_scheduler *vblank_scheduler;
 
 	/// Render statistics
 	struct render_statistics render_stats;
@@ -245,8 +236,18 @@ typedef struct session {
 	options_t o;
 	/// Whether we have hit unredirection timeout.
 	bool tmout_unredir_hit;
-	/// Whether we need to redraw the screen
-	bool redraw_needed;
+	/// If the backend is busy. This means two things:
+	/// Either the backend is currently rendering a frame, or a frame has been
+	/// rendered but has yet to be presented. In either case, we should not start
+	/// another render right now. As if we start issuing rendering commands now, we
+	/// will have to wait for either the the current render to finish, or the current
+	/// back buffer to be become available again. In either case, we will be wasting
+	/// time.
+	bool backend_busy;
+	/// Whether a render is queued. This generally means there are pending updates
+	/// to the screen that's neither included in the current render, nor on the
+	/// screen.
+	bool render_queued;
 
 	/// Cache a xfixes region so we don't need to allocate it every time.
 	/// A workaround for yshui/picom#301

src/config.c

@@ -8,6 +8,8 @@
 #include <limits.h>
 #include <math.h>
 #include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -615,6 +617,82 @@
 	return ret;
 }
 
+struct debug_options_entry {
+	const char *name;
+	const char **choices;
+	size_t offset;
+};
+
+// clang-format off
+const char *vblank_scheduler_str[] = {
+	[VBLANK_SCHEDULER_PRESENT] = "present",
+	[VBLANK_SCHEDULER_SGI_VIDEO_SYNC] = "sgi_video_sync",
+	[LAST_VBLANK_SCHEDULER] = NULL
+};
+static const struct debug_options_entry debug_options_entries[] = {
+    {"smart_frame_pacing", NULL,                 offsetof(struct debug_options, smart_frame_pacing)},
+    {"force_vblank_sched", vblank_scheduler_str, offsetof(struct debug_options, force_vblank_scheduler)},
+};
+// clang-format on
+
+void parse_debug_option_single(char *setting, struct debug_options *debug_options) {
+	char *equal = strchr(setting, '=');
+	size_t name_len = equal ? (size_t)(equal - setting) : strlen(setting);
+	for (size_t i = 0; i < ARR_SIZE(debug_options_entries); i++) {
+		if (strncmp(setting, debug_options_entries[i].name, name_len) != 0) {
+			continue;
+		}
+		if (debug_options_entries[i].name[name_len] != '\0') {
+			continue;
+		}
+		auto value = (int *)((void *)debug_options + debug_options_entries[i].offset);
+		if (equal) {
+			const char *const arg = equal + 1;
+			if (debug_options_entries[i].choices != NULL) {
+				for (size_t j = 0; debug_options_entries[i].choices[j]; j++) {
+					if (strcmp(arg, debug_options_entries[i].choices[j]) ==
+					    0) {
+						*value = (int)j;
+						return;
+					}
+				}
+			}
+			if (!parse_int(arg, value)) {
+				log_error("Invalid value for debug option %s: %s, it "
+				          "will be ignored.",
+				          debug_options_entries[i].name, arg);
+			}
+		} else if (debug_options_entries[i].choices == NULL) {
+			*value = 1;
+		} else {
+			log_error(
+			    "Missing value for debug option %s, it will be ignored.", setting);
+		}
+		return;
+	}
+	log_error("Invalid debug option: %s", setting);
+}
+
+/// Parse debug options from environment variable `PICOM_DEBUG`.
+void parse_debug_options(struct debug_options *debug_options) {
+	const char *debug = getenv("PICOM_DEBUG");
+	const struct debug_options default_debug_options = {
+	    .force_vblank_scheduler = LAST_VBLANK_SCHEDULER,
+	};
+
+	*debug_options = default_debug_options;
+	if (!debug) {
+		return;
+	}
+
+	scoped_charp debug_copy = strdup(debug);
+	char *tmp, *needle = strtok_r(debug_copy, ";", &tmp);
+	while (needle) {
+		parse_debug_option_single(needle, debug_options);
+		needle = strtok_r(NULL, ";", &tmp);
+	}
+}
+
 /**
  * Parse a list of window shader rules.
  */
@@ -817,5 +895,6 @@
 	(void)hasneg;
 	(void)winopt_mask;
 #endif
+	parse_debug_options(&opt->debug_options);
 	return ret;
 }

src/config.h

@@ -73,6 +73,27 @@ enum blur_method {
 
 typedef struct _c2_lptr c2_lptr_t;
 
+enum vblank_scheduler_type {
+	/// X Present extension based vblank events
+	VBLANK_SCHEDULER_PRESENT,
+	/// GLX_SGI_video_sync based vblank events
+	VBLANK_SCHEDULER_SGI_VIDEO_SYNC,
+	/// An invalid scheduler, served as a scheduler count, and
+	/// as a sentinel value.
+	LAST_VBLANK_SCHEDULER,
+};
+
+extern const char *vblank_scheduler_str[];
+
+/// Internal, private options for debugging and development use.
+struct debug_options {
+	/// Try to reduce frame latency by using vblank interval and render time
+	/// estimates. Right now it's not working well across drivers.
+	int smart_frame_pacing;
+	/// Override the vblank scheduler chosen by the compositor.
+	int force_vblank_scheduler;
+};
+
 /// Structure representing all options.
 typedef struct options {
 	// === Debugging ===
@@ -262,6 +283,8 @@ typedef struct options {
 	c2_lptr_t *transparent_clipping_blacklist;
 
 	bool dithered_present;
+
+	struct debug_options debug_options;
 } options_t;
 
 extern const char *const BACKEND_STRS[NUM_BKEND + 1];

src/event.c

@@ -716,7 +716,8 @@ void ev_handle(session_t *ps, xcb_generic_event_t *ev) {
 	// XXX redraw needs to be more fine grained
 	queue_redraw(ps);
 
-	// the events sent from SendEvent will be ignored
+	// We intentionally ignore events sent via SendEvent. Those events has the 8th bit
+	// of response_type set, meaning they will match none of the cases below.
 	switch (ev->response_type) {
 	case FocusIn: ev_focus_in(ps, (xcb_focus_in_event_t *)ev); break;
 	case FocusOut: ev_focus_out(ps, (xcb_focus_out_event_t *)ev); break;

src/meson.build

@@ -9,7 +9,8 @@ base_deps = [
 
 srcs = [ files('picom.c', 'win.c', 'c2.c', 'x.c', 'config.c', 'vsync.c', 'utils.c',
                'diagnostic.c', 'string_utils.c', 'render.c', 'kernel.c', 'log.c',
-               'options.c', 'event.c', 'cache.c', 'atom.c', 'file_watch.c', 'statistics.c') ]
+               'options.c', 'event.c', 'cache.c', 'atom.c', 'file_watch.c', 'statistics.c',
+               'vblank.c') ]
 picom_inc = include_directories('.')
 
 cflags = []
@@ -58,7 +59,7 @@ endif
 
 if get_option('opengl')
 	cflags += ['-DCONFIG_OPENGL', '-DGL_GLEXT_PROTOTYPES']
-	deps += [dependency('gl', required: true), dependency('egl', required: true)]
+	deps += [dependency('gl', required: true), dependency('egl', required: true), dependency('threads', required:true)]
 	srcs += [ 'opengl.c' ]
 endif