[client] egl: use eglSwapBuffersWithDamageKHR for cursor-only updates

Instead of damaging the entire surface when rendering a cursor move,
we can use the EGL_KHR_swap_buffers_with_damage extension to only
damage the part of the window covered by the cursor. This should
reduce the cursor movement latency on Wayland.

client/displayservers/Wayland/gl.c

@@ -41,6 +41,7 @@ bool waylandEGLInit(int w, int h)
     DEBUG_ERROR("Failed to create EGL window");
     return false;
   }
+
   return true;
 }
 
@@ -68,9 +69,51 @@ EGLDisplay waylandGetEGLDisplay(void)
   return eglGetDisplay(native);
 }
 
-void waylandEGLSwapBuffers(EGLDisplay display, EGLSurface surface)
+void waylandEGLSwapBuffers(EGLDisplay display, EGLSurface surface, const struct Rect * damage, int count)
 {
-  eglSwapBuffers(display, surface);
+  if (!wlWm.eglSwapWithDamageInit)
+  {
+    const char *exts = eglQueryString(display, EGL_EXTENSIONS);
+    wlWm.eglSwapWithDamageInit = true;
+    if (wl_proxy_get_version((struct wl_proxy *) wlWm.surface) < 4)
+      DEBUG_INFO("Swapping buffers with damage: not supported, need wl_compositor v4");
+    else if (strstr(exts, "EGL_KHR_swap_buffers_with_damage") && g_egl_dynProcs.eglSwapBuffersWithDamageKHR)
+    {
+      wlWm.eglSwapWithDamage = g_egl_dynProcs.eglSwapBuffersWithDamageKHR;
+      DEBUG_INFO("Using EGL_KHR_swap_buffers_with_damage");
+    }
+    else if (strstr(exts, "EGL_EXT_swap_buffers_with_damage") && g_egl_dynProcs.eglSwapBuffersWithDamageEXT)
+    {
+      wlWm.eglSwapWithDamage = g_egl_dynProcs.eglSwapBuffersWithDamageEXT;
+      DEBUG_INFO("Using EGL_EXT_swap_buffers_with_damage");
+    }
+    else
+      DEBUG_INFO("Swapping buffers with damage: not supported");
+  }
+
+  if (wlWm.eglSwapWithDamage && count)
+  {
+    if (count * 4 > wlWm.eglDamageRectCount)
+    {
+      free(wlWm.eglDamageRects);
+      wlWm.eglDamageRects = malloc(sizeof(EGLint) * count * 4);
+      if (!wlWm.eglDamageRects)
+        DEBUG_FATAL("Out of memory");
+      wlWm.eglDamageRectCount = count * 4;
+    }
+
+    for (int i = 0; i < count; ++i)
+    {
+      wlWm.eglDamageRects[i*4+0] = damage[i].x;
+      wlWm.eglDamageRects[i*4+1] = damage[i].y;
+      wlWm.eglDamageRects[i*4+2] = damage[i].w;
+      wlWm.eglDamageRects[i*4+3] = damage[i].h;
+    }
+
+    wlWm.eglSwapWithDamage(display, surface, wlWm.eglDamageRects, count);
+  }
+  else
+    eglSwapBuffers(display, surface);
 
   if (wlWm.needsResize)
   {
@@ -169,6 +212,6 @@ void waylandGLSetSwapInterval(int interval)
 
 void waylandGLSwapBuffers(void)
 {
-  waylandEGLSwapBuffers(wlWm.glDisplay, wlWm.glSurface);
+  waylandEGLSwapBuffers(wlWm.glDisplay, wlWm.glSurface, NULL, 0);
 }
 #endif

client/displayservers/Wayland/registry.c

@@ -37,7 +37,9 @@ static void registryGlobalHandler(void * data, struct wl_registry * registry,
   else if (!strcmp(interface, wl_shm_interface.name))
     wlWm.shm = wl_registry_bind(wlWm.registry, name, &wl_shm_interface, 1);
   else if (!strcmp(interface, wl_compositor_interface.name) && version >= 3)
-    wlWm.compositor = wl_registry_bind(wlWm.registry, name, &wl_compositor_interface, 3);
+    wlWm.compositor = wl_registry_bind(wlWm.registry, name,
+        // we only need v3 to run, but v4 can use eglSwapBuffersWithDamageKHR
+        &wl_compositor_interface, version > 4 ? 4 : version);
 #ifndef ENABLE_LIBDECOR
   else if (!strcmp(interface, xdg_wm_base_interface.name))
     wlWm.xdgWmBase = wl_registry_bind(wlWm.registry, name, &xdg_wm_base_interface, 1);

client/displayservers/Wayland/wayland.h

@@ -29,6 +29,7 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 # include <EGL/eglext.h>
 #endif
 
+#include "egl_dynprocs.h"
 #include "common/locking.h"
 #include "common/countedbuffer.h"
 #include "interface/displayserver.h"
@@ -66,6 +67,13 @@ struct SurfaceOutput
   struct wl_list link;
 };
 
+enum EGLSwapWithDamageState {
+  SWAP_WITH_DAMAGE_UNKNOWN,
+  SWAP_WITH_DAMAGE_UNSUPPORTED,
+  SWAP_WITH_DAMAGE_KHR,
+  SWAP_WITH_DAMAGE_EXT,
+};
+
 struct WaylandDSState
 {
   bool pointerGrabbed;
@@ -88,8 +96,12 @@ struct WaylandDSState
   bool warpSupport;
   double cursorX, cursorY;
 
-#ifdef ENABLE_EGL
+#if defined(ENABLE_EGL) || defined(ENABLE_OPENGL)
   struct wl_egl_window * eglWindow;
+  bool eglSwapWithDamageInit;
+  eglSwapBuffersWithDamageKHR_t eglSwapWithDamage;
+  EGLint * eglDamageRects;
+  int eglDamageRectCount;
 #endif
 
 #ifdef ENABLE_OPENGL
@@ -197,7 +209,7 @@ void waylandShowPointer(bool show);
 #if defined(ENABLE_EGL) || defined(ENABLE_OPENGL)
 bool waylandEGLInit(int w, int h);
 EGLDisplay waylandGetEGLDisplay(void);
-void waylandEGLSwapBuffers(EGLDisplay display, EGLSurface surface);
+void waylandEGLSwapBuffers(EGLDisplay display, EGLSurface surface, const struct Rect * damage, int count);
 #endif
 
 #ifdef ENABLE_EGL

client/displayservers/Wayland/window.c

@@ -114,5 +114,3 @@ bool waylandIsValidPointerPos(int x, int y)
 {
   return x >= 0 && x < wlWm.width && y >= 0 && y < wlWm.height;
 }
-
-