Improvement: Enhance --glx-swap-method

- Enhance --glx-swap-method to support longer buffers ages (3-6), and
  automatic buffer age detection via GLX_EXT_buffer_age.

common.h

@@ -64,6 +64,7 @@
 #include <sys/poll.h>
 #include <assert.h>
 #include <time.h>
+#include <ctype.h>
 #include <sys/time.h>
 
 #include <X11/Xlib.h>
@@ -107,6 +108,10 @@
 #define GL_TEXTURE_RECTANGLE 0x84F5
 #endif
 
+#ifndef GLX_BACK_BUFFER_AGE_EXT
+#define GLX_BACK_BUFFER_AGE_EXT 0x20F4
+#endif
+
 #endif
 
 // === Macros ===
@@ -175,6 +180,9 @@
 /// @brief Maximum OpenGL FBConfig depth.
 #define OPENGL_MAX_DEPTH 32
 
+/// @brief Maximum OpenGL buffer age.
+#define CGLX_MAX_BUFFER_AGE 5
+
 // Window flags
 
 // Window size is changed
@@ -285,11 +293,11 @@ enum backend {
 };
 
 /// @brief Possible swap methods.
-enum glx_swap_method {
-  SWAPM_UNDEFINED,
-  SWAPM_EXCHANGE,
-  SWAPM_COPY,
-  NUM_SWAPM,
+enum {
+  SWAPM_BUFFER_AGE = -1,
+  SWAPM_UNDEFINED = 0,
+  SWAPM_COPY = 1,
+  SWAPM_EXCHANGE = 2,
 };
 
 typedef struct _glx_texture glx_texture_t;
@@ -383,7 +391,7 @@ typedef struct {
   /// Whether to avoid rebinding pixmap on window damage.
   bool glx_no_rebind_pixmap;
   /// GLX swap method we assume OpenGL uses.
-  enum glx_swap_method glx_swap_method;
+  int glx_swap_method;
   /// Whether to try to detect WM windows and mark them as focused.
   bool mark_wmwin_focused;
   /// Whether to mark override-redirect windows as focused.
@@ -576,7 +584,7 @@ typedef struct {
   /// The region needs to painted on next paint.
   XserverRegion all_damage;
   /// The region damaged on the last paint.
-  XserverRegion all_damage_last;
+  XserverRegion all_damage_last[CGLX_MAX_BUFFER_AGE];
   /// Whether all windows are currently redirected.
   bool redirected;
   /// Whether there's a highest full-screen window, and all windows could
@@ -958,7 +966,6 @@ typedef enum {
 extern const char * const WINTYPES[NUM_WINTYPES];
 extern const char * const VSYNC_STRS[NUM_VSYNC + 1];
 extern const char * const BACKEND_STRS[NUM_BKEND + 1];
-extern const char * const GLX_SWAP_METHODS_STRS[NUM_SWAPM + 1];
 extern session_t *ps_g;
 
 // == Debugging code ==
@@ -1357,13 +1364,51 @@ parse_backend(session_t *ps, const char *str) {
  */
 static inline bool
 parse_glx_swap_method(session_t *ps, const char *str) {
-  for (enum glx_swap_method i = 0; GLX_SWAP_METHODS_STRS[i]; ++i)
-    if (!strcasecmp(str, GLX_SWAP_METHODS_STRS[i])) {
-      ps->o.glx_swap_method = i;
-      return true;
+  // Parse alias
+  if (!strcmp("undefined", str)) {
+    ps->o.glx_swap_method = 0;
+    return true;
+  }
+
+  if (!strcmp("copy", str)) {
+    ps->o.glx_swap_method = 1;
+    return true;
+  }
+
+  if (!strcmp("exchange", str)) {
+    ps->o.glx_swap_method = 2;
+    return true;
+  }
+
+  if (!strcmp("buffer-age", str)) {
+    ps->o.glx_swap_method = -1;
+    return true;
+  }
+
+  // Parse number
+  {
+    char *pc = NULL;
+    int age = strtol(str, &pc, 0);
+    if (!pc || str == pc) {
+      printf_errf("(\"%s\"): Invalid number.", str);
+      return false;
     }
-  printf_errf("(\"%s\"): Invalid GLX swap method argument.", str);
-  return false;
+
+    for (; *pc; ++pc)
+      if (!isspace(*pc)) {
+        printf_errf("(\"%s\"): Trailing characters.", str);
+        return false;
+      }
+
+    if (age > CGLX_MAX_BUFFER_AGE + 1 || age < -1) {
+      printf_errf("(\"%s\"): Number too large / too small.", str);
+      return false;
+    }
+
+    ps->o.glx_swap_method = age;
+  }
+
+  return true;
 }
 
 timeout_t *

compton.c

@@ -50,14 +50,6 @@ const char * const BACKEND_STRS[NUM_BKEND + 1] = {
   NULL
 };
 
-/// Names of GLX swap methods.
-const char * const GLX_SWAP_METHODS_STRS[NUM_SWAPM + 1] = {
-  "undefined",    // SWAPM_UNDEFINED
-  "exchange",     // SWAPM_EXCHANGE
-  "copy",         // SWAPM_COPY
-  NULL
-};
-
 /// Function pointers to init VSync modes.
 static bool (* const (VSYNC_FUNCS_INIT[NUM_VSYNC]))(session_t *ps) = {
   [VSYNC_DRM          ] = vsync_drm_init,
@@ -4266,12 +4258,14 @@ usage(void) {
     "  GLX backend: Avoid rebinding pixmap on window damage. Probably\n"
     "  could improve performance on rapid window content changes, but is\n"
     "  known to break things on some drivers.\n"
-    "--glx-swap-method undefined/exchange/copy\n"
+    "--glx-swap-method undefined/copy/exchange/3/4/5/6/buffer-age\n"
     "  GLX backend: GLX buffer swap method we assume. Could be\n"
-    "  \"undefined\", \"exchange\", or \"copy\". \"undefined\" is the slowest\n"
-    "  and the safest; \"exchange\" and \"copy\" are faster but may fail on\n"
-    "  some drivers. Useless with --glx-use-copysubbuffermesa. Defaults to\n"
-    "  \"undefined\".\n"
+    "  undefined (0), copy (1), exchange (2), 3-6, or buffer-age (-1).\n"
+    "  \"undefined\" is the slowest and the safest, and the default value.\n"
+    "  1 is fastest, but may fail on some drivers, 2-6 are gradually slower\n"
+    "  but safer (6 is still faster than 0). -1 means auto-detect using\n"
+    "  GLX_EXT_buffer_age, supported by some drivers. Useless with\n"
+    "  --glx-use-copysubbuffermesa.\n"
 #undef WARNING
 #ifndef CONFIG_DBUS
 #define WARNING WARNING_DISABLED
@@ -6027,7 +6021,7 @@ session_init(session_t *ps_old, int argc, char **argv) {
     .tmout_lst = NULL,
 
     .all_damage = None,
-    .all_damage_last = None,
+    .all_damage_last = { None },
     .time_start = { 0, 0 },
     .redirected = false,
     .unredir_possible = false,
@@ -6478,7 +6472,8 @@ session_destroy(session_t *ps) {
   free_root_tile(ps);
   free_region(ps, &ps->screen_reg);
   free_region(ps, &ps->all_damage);
-  free_region(ps, &ps->all_damage_last);
+  for (int i = 0; i < CGLX_MAX_BUFFER_AGE; ++i)
+    free_region(ps, &ps->all_damage_last[i]);
   free(ps->expose_rects);
   free(ps->shadow_corner);
   free(ps->shadow_top);

dbus.c

@@ -914,11 +914,7 @@ cdbus_process_opts_get(session_t *ps, DBusMessage *msg) {
   cdbus_m_opts_get_do(glx_copy_from_front, cdbus_reply_bool);
   cdbus_m_opts_get_do(glx_use_copysubbuffermesa, cdbus_reply_bool);
   cdbus_m_opts_get_do(glx_no_rebind_pixmap, cdbus_reply_bool);
-  if (!strcmp("glx_swap_method", target)) {
-    assert(ps->o.glx_swap_method < sizeof(GLX_SWAP_METHODS_STRS) / sizeof(GLX_SWAP_METHODS_STRS[0]));
-    cdbus_reply_string(ps, msg, GLX_SWAP_METHODS_STRS[ps->o.glx_swap_method]);
-    return true;
-  }
+  cdbus_m_opts_get_do(glx_swap_method, cdbus_reply_int32);
 #endif
 
   cdbus_m_opts_get_do(track_focus, cdbus_reply_bool);

opengl.c

@@ -54,18 +54,20 @@ glx_init(session_t *ps, bool need_render) {
   if (need_render && !glx_hasglxext(ps, "GLX_EXT_texture_from_pixmap"))
     goto glx_init_end;
 
-  // Get GLX context
-  ps->glx_context = glXCreateContext(ps->dpy, pvis, None, GL_TRUE);
-
   if (!ps->glx_context) {
-    printf_errf("(): Failed to get GLX context.");
-    goto glx_init_end;
-  }
+    // Get GLX context
+    ps->glx_context = glXCreateContext(ps->dpy, pvis, None, GL_TRUE);
 
-  // Attach GLX context
-  if (!glXMakeCurrent(ps->dpy, get_tgt_window(ps), ps->glx_context)) {
-    printf_errf("(): Failed to attach GLX context.");
-    goto glx_init_end;
+    if (!ps->glx_context) {
+      printf_errf("(): Failed to get GLX context.");
+      goto glx_init_end;
+    }
+
+    // Attach GLX context
+    if (!glXMakeCurrent(ps->dpy, get_tgt_window(ps), ps->glx_context)) {
+      printf_errf("(): Failed to attach GLX context.");
+      goto glx_init_end;
+    }
   }
 
   // Ensure we have a stencil buffer. X Fixes does not guarantee rectangles
@@ -111,6 +113,7 @@ glx_init(session_t *ps, bool need_render) {
   if (need_render && !glx_update_fbconfig(ps))
     goto glx_init_end;
 
+  // Render preparations
   if (need_render) {
     glx_on_root_change(ps);
 
@@ -588,20 +591,44 @@ glx_paint_pre(session_t *ps, XserverRegion *preg) {
   ps->glx_z = 0.0;
   // glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
-  // Exchange swap is interested in the raw damaged region only
-  XserverRegion all_damage_last = ps->all_damage_last;
-  ps->all_damage_last = None;
-  if (SWAPM_EXCHANGE == ps->o.glx_swap_method && *preg)
-    ps->all_damage_last = copy_region(ps, *preg);
+  // Get buffer age
+  int buffer_age = ps->o.glx_swap_method;
+  bool trace_damage = (ps->o.glx_swap_method < 0 || ps->o.glx_swap_method > 1);
+
+  // Query GLX_EXT_buffer_age for buffer age
+  if (SWAPM_BUFFER_AGE == buffer_age) {
+    unsigned val = 0;
+    glXQueryDrawable(ps->dpy, get_tgt_window(ps),
+        GLX_BACK_BUFFER_AGE_EXT, &val);
+    buffer_age = val;
+  }
+
+  // Buffer age too high
+  if (buffer_age > CGLX_MAX_BUFFER_AGE + 1)
+    buffer_age = 0;
+
+  // Make sure buffer age >= 0
+  buffer_age = max_i(buffer_age, 0);
+
+  // Trace raw damage regions
+  XserverRegion newdamage = None;
+  if (trace_damage && *preg)
+    newdamage = copy_region(ps, *preg);
 
   // OpenGL doesn't support partial repaint without GLX_MESA_copy_sub_buffer,
   // we could redraw the whole screen or copy unmodified pixels from
   // front buffer with --glx-copy-from-front.
-  if (ps->o.glx_use_copysubbuffermesa || SWAPM_COPY == ps->o.glx_swap_method
-      || !*preg) {
+  if (ps->o.glx_use_copysubbuffermesa || 1 == buffer_age || !*preg) {
   }
-  else if (SWAPM_EXCHANGE == ps->o.glx_swap_method && all_damage_last) {
-    XFixesUnionRegion(ps->dpy, *preg, *preg, all_damage_last);
+  else if (buffer_age > 1) {
+    for (int i = 0; i < buffer_age - 1; ++i) {
+      XserverRegion dmg = ps->all_damage_last[i];
+      if (!dmg) {
+        free_region(ps, preg);
+        break;
+      }
+      XFixesUnionRegion(ps->dpy, *preg, *preg, dmg);
+    }
   }
   else if (!ps->o.glx_copy_from_front) {
     free_region(ps, preg);
@@ -625,7 +652,12 @@ glx_paint_pre(session_t *ps, XserverRegion *preg) {
     }
   }
 
-  free_region(ps, &all_damage_last);
+  if (trace_damage) {
+    free_region(ps, &ps->all_damage_last[CGLX_MAX_BUFFER_AGE - 1]);
+    memmove(ps->all_damage_last + 1, ps->all_damage_last,
+        (CGLX_MAX_BUFFER_AGE - 1) * sizeof(XserverRegion));
+    ps->all_damage_last[0] = newdamage;
+  }
 
   glx_set_clip(ps, *preg, NULL);