Improvement: GLX: Use SCISSOR_TEST instead of STENCIL_TEST when possible

- GLX backend: Use GL_SCISSOR_TEST instead of STENCIL_TEST if there's
  only one rectangle in glx_set_clip(). Profiling with gDebugger shows a
  10% performance improvement.

- Add .desktop installation rules. (#97)

Makefile

@@ -6,6 +6,7 @@ CC ?= gcc
 PREFIX ?= /usr
 BINDIR ?= $(PREFIX)/bin
 MANDIR ?= $(PREFIX)/share/man/man1
+APPDIR ?= $(PREFIX)/share/applications
 
 PACKAGES = x11 xcomposite xfixes xdamage xrender xext xrandr
 LIBS = -lm -lrt
@@ -79,7 +80,8 @@ else
   export LD_ALTEXEC = /usr/bin/ld.gold
   OBJS += backtrace-symbols.o
   LIBS += -lbfd
-  CFLAGS += -ggdb -Weverything -Wno-disabled-macro-expansion -Wno-padded -Wno-gnu
+  CFLAGS += -ggdb
+  # CFLAGS += -Weverything -Wno-disabled-macro-expansion -Wno-padded -Wno-gnu
 endif
 
 LIBS += $(shell pkg-config --libs $(PACKAGES))
@@ -112,9 +114,10 @@ man/%.1.html: man/%.1.asciidoc
 docs: $(MANPAGES) $(MANPAGES_HTML)
 
 install: $(BINS) docs
-	@install -d "$(DESTDIR)$(BINDIR)" "$(DESTDIR)$(MANDIR)"
+	@install -d "$(DESTDIR)$(BINDIR)" "$(DESTDIR)$(MANDIR)" "$(DESTDIR)$(APPDIR)"
 	@install -m755 $(BINS) "$(DESTDIR)$(BINDIR)"/ 
 	@install -m644 $(MANPAGES) "$(DESTDIR)$(MANDIR)"/
+	@install -m644 compton.desktop "$(DESTDIR)$(APPDIR)"/
 ifneq "$(DOCDIR)" ""
 	@install -d "$(DESTDIR)$(DOCDIR)"
 	@install -m644 README.md compton.sample.conf "$(DESTDIR)$(DOCDIR)"/
@@ -124,6 +127,7 @@ endif
 uninstall:
 	@rm -f "$(DESTDIR)$(BINDIR)/compton" "$(DESTDIR)$(BINDIR)/compton-trans"
 	@rm -f $(addprefix "$(DESTDIR)$(MANDIR)"/, compton.1 compton-trans.1)
+	@rm -f "$(DESTDIR)$(APPDIR)/compton.desktop"
 ifneq "$(DOCDIR)" ""
 	@rm -f $(addprefix "$(DESTDIR)$(DOCDIR)"/, README.md compton.sample.conf cdbus-driver.sh)
 endif

src/compton.c

@@ -4136,7 +4136,7 @@ usage(void) {
     "--glx-no-stencil\n"
     "  Avoid using stencil buffer under GLX backend. Might cause issues\n"
     "  when rendering transparent content, may have a positive or\n"
-    "  negative effect on performance.\n"
+    "  negative effect on performance. (My test shows a 10% slowdown.)\n"
 #undef WARNING
 #ifndef CONFIG_DBUS
 #define WARNING WARNING_DISABLED

src/opengl.c

@@ -487,7 +487,31 @@ glx_set_clip(session_t *ps, XserverRegion reg) {
   if (ps->o.glx_no_stencil)
     return;
 
-  if (reg) {
+  static XRectangle rect_blank = {
+    .x = 0, .y = 0, .width = 0, .height = 0
+  };
+
+  glDisable(GL_STENCIL_TEST);
+  glDisable(GL_SCISSOR_TEST);
+
+  if (!reg)
+    return;
+
+  int nrects = 0;
+  XRectangle *rects = XFixesFetchRegion(ps->dpy, reg, &nrects);
+  if (!nrects) {
+    if (rects) XFree(rects);
+    nrects = 1;
+    rects = &rect_blank;
+  }
+
+  assert(nrects);
+  if (1 == nrects) {
+    glEnable(GL_SCISSOR_TEST);
+    glScissor(rects[0].x, ps->root_height - rects[0].y - rects[0].height,
+        rects[0].width, rects[0].height);
+  }
+  else {
     glEnable(GL_STENCIL_TEST);
     glClear(GL_STENCIL_BUFFER_BIT);
 
@@ -495,8 +519,6 @@ glx_set_clip(session_t *ps, XserverRegion reg) {
     glDepthMask(GL_FALSE);
     glStencilOp(GL_REPLACE, GL_KEEP, GL_KEEP);
 
-    int nrects = 0;
-    XRectangle *rects = XFixesFetchRegion(ps->dpy, reg, &nrects);
 
     glBegin(GL_QUADS);
 
@@ -519,16 +541,13 @@ glx_set_clip(session_t *ps, XserverRegion reg) {
 
     glEnd();
 
-    if (rects)
-      XFree(rects);
-
     glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
     glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
     glDepthMask(GL_TRUE);
   }
-  else {
+
-    glDisable(GL_STENCIL_TEST);
+  if (rects && &rect_blank != rects)
-  }
+    XFree(rects);
 }
 
 /**