Improvement: --resize-damage

- Add --resize-damage to enlarge/shrink repaint region by a specific
  number of pixels, used for solving the line corruption issue with
  blur. Thanks to Nuck and jerri in #104 for reporting.

- Fix the memory leak of blur shader string.

common.h

@@ -403,6 +403,8 @@ typedef struct {
   /// Whether to paint on X Composite overlay window instead of root
   /// window.
   bool paint_on_overlay;
+  /// Resize damage for a specific number of pixels.
+  int resize_damage;
   /// Whether to unredirect all windows if a full-screen opaque window
   /// is detected.
   bool unredir_if_possible;

compton.c

@@ -4235,6 +4235,11 @@ usage(void) {
     "    --blur-kern '7,7,0.000003,0.000102,0.000849,0.001723,0.000849,0.000102,0.000003,0.000102,0.003494,0.029143,0.059106,0.029143,0.003494,0.000102,0.000849,0.029143,0.243117,0.493069,0.243117,0.029143,0.000849,0.001723,0.059106,0.493069,0.493069,0.059106,0.001723,0.000849,0.029143,0.243117,0.493069,0.243117,0.029143,0.000849,0.000102,0.003494,0.029143,0.059106,0.029143,0.003494,0.000102,0.000003,0.000102,0.000849,0.001723,0.000849,0.000102,0.000003'\n"
     "--blur-background-exclude condition\n"
     "  Exclude conditions for background blur.\n"
+    "--resize-damage integer\n"
+    "  Resize damaged region by a specific number of pixels. A positive\n"
+    "  value enlarges it while a negative one shrinks it. Useful for\n"
+    "  fixing the line corruption issues of blur. May or may not\n"
+    "  work with --glx-no-stencil. Shrinking doesn't function correctly.\n"
     "--invert-color-include condition\n"
     "  Specify a list of conditions of windows that should be painted with\n"
     "  inverted color. Resource-hogging, and is not well tested.\n"
@@ -4861,6 +4866,7 @@ get_cfg(session_t *ps, int argc, char *const *argv, bool first_pass) {
     { "glx-swap-method", required_argument, NULL, 299 },
     { "fade-exclude", required_argument, NULL, 300 },
     { "blur-kern", required_argument, NULL, 301 },
+    { "resize-damage", required_argument, NULL, 302 },
     // Must terminate with a NULL entry
     { NULL, 0, NULL, 0 },
   };
@@ -5089,6 +5095,9 @@ get_cfg(session_t *ps, int argc, char *const *argv, bool first_pass) {
         free(ps->o.blur_kern);
         if (!(ps->o.blur_kern = parse_matrix(ps, optarg)))
           exit(1);
+      case 302:
+        // --resize-damage
+        ps->o.resize_damage = atoi(optarg);
         break;
       default:
         usage();
@@ -5952,6 +5961,7 @@ session_init(session_t *ps_old, int argc, char **argv) {
       .synchronize = false,
       .detect_rounded_corners = false,
       .paint_on_overlay = false,
+      .resize_damage = 0,
       .unredir_if_possible = false,
       .dbus = false,
       .benchmark = 0,
@@ -6577,6 +6587,7 @@ session_run(session_t *ps) {
     if (!ps->redirected)
       free_region(ps, &ps->all_damage);
 
+    resize_region(ps, ps->all_damage, ps->o.resize_damage);
     if (ps->all_damage && !is_region_empty(ps, ps->all_damage, NULL)) {
       static int paint = 0;
       paint_all(ps, ps->all_damage, t);

compton.h

@@ -850,19 +850,69 @@ get_screen_region(session_t *ps) {
   return XFixesCreateRegion(ps->dpy, &r, 1);
 }
 
+/**
+ * Resize a region.
+ */
+static inline void
+resize_region(session_t *ps, XserverRegion region, short mod) {
+  if (!mod || !region) return;
+
+  int nrects = 0, nnewrects = 0;
+  XRectangle *newrects = NULL;
+  XRectangle *rects = XFixesFetchRegion(ps->dpy, region, &nrects);
+  if (!rects || !nrects)
+    goto resize_region_end;
+
+  // Allocate memory for new rectangle list, because I don't know if it's
+  // safe to write in the memory Xlib allocates
+  newrects = calloc(nrects, sizeof(XRectangle));
+  if (!newrects) {
+    printf_errf("(): Failed to allocate memory.");
+    exit(1);
+  }
+
+  // Loop through all rectangles
+  for (int i = 0; i < nrects; ++i) {
+    int x1 = max_i(rects[i].x - mod, 0);
+    int y1 = max_i(rects[i].y - mod, 0);
+    int x2 = min_i(rects[i].x + rects[i].width + mod, ps->root_width);
+    int y2 = min_i(rects[i].y + rects[i].height + mod, ps->root_height);
+    int wid = x2 - x1;
+    int hei = y2 - y1;
+    if (wid <= 0 || hei <= 0)
+      continue;
+    newrects[nnewrects].x = x1;
+    newrects[nnewrects].y = y1;
+    newrects[nnewrects].width = wid;
+    newrects[nnewrects].height = hei;
+    ++nnewrects;
+  }
+
+  // Set region
+  XFixesSetRegion(ps->dpy, region, newrects, nnewrects);
+
+resize_region_end:
+  cxfree(rects);
+  free(newrects);
+}
+
 /**
  * Dump a region.
  */
 static inline void
 dump_region(const session_t *ps, XserverRegion region) {
-  int nrects = 0, i;
-  XRectangle *rects = XFixesFetchRegion(ps->dpy, region, &nrects);
-  if (!rects)
-    return;
+  int nrects = 0;
+  XRectangle *rects = NULL;
+  if (!rects && region)
+    rects = XFixesFetchRegion(ps->dpy, region, &nrects);
 
-  for (i = 0; i < nrects; ++i)
+  printf_dbgf("(%#010lx): %d rects\n", region, nrects);
+  if (!rects) return;
+  for (int i = 0; i < nrects; ++i)
     printf("Rect #%d: %8d, %8d, %8d, %8d\n", i, rects[i].x, rects[i].y,
         rects[i].width, rects[i].height);
+  putchar('\n');
+  fflush(stdout);
 
   cxfree(rects);
 }

opengl.c

@@ -246,6 +246,7 @@ glx_init_blur(session_t *ps) {
 #endif
     }
     ps->glx_frag_shader_blur = glx_create_shader(GL_FRAGMENT_SHADER, shader_str);
+    free(shader_str);
   }
 
   if (!ps->glx_frag_shader_blur) {