Exclude transparent-clipping-excluded windows from updating the ignored region

Transparent clipping interacts poorly with programs whose transparent
interface elements must show windows below them for functionality,
for example screenshot utilities.

man/picom.1.asciidoc

@@ -259,6 +259,9 @@ May also be one of the predefined kernels: `3x3box` (default), `5x5box`, `7x7box
 *--transparent-clipping*::
 	Make transparent windows clip other windows like non-transparent windows do, instead of blending on top of them.
 
+*--transparent-clipping-exclude* 'CONDITION'::
+	Specify a list of conditions of windows that should never have transparent clipping applied. Useful for screenshot tools, where you need to be able to see through transparent parts of the window.
+
 *--window-shader-fg* 'SHADER'::
 	Specify GLSL fragment shader path for rendering window contents. Does not work when *--legacy-backends* is enabled. Shader is searched first relative to the directory the configuration file is in, then in the usual places for a configuration file. See section *SHADER INTERFACE* below for more details on the interface.
 

picom.sample.conf

@@ -355,6 +355,12 @@ use-damage = true;
 #
 # transparent-clipping = false
 
+# Specify a list of conditions of windows that should never have transparent
+# clipping applied. Useful for screenshot tools, where you need to be able to
+# see through transparent parts of the window.
+#
+# transparent-clipping-exclude = []
+
 # Set the log level. Possible values are:
 #  "trace", "debug", "info", "warn", "error"
 # in increasing level of importance. Case doesn't matter.

src/config.h

@@ -253,6 +253,9 @@ typedef struct options {
 	// Make transparent windows clip other windows, instead of blending on top of
 	// them
 	bool transparent_clipping;
+	/// A list of conditions of windows to which transparent clipping
+	/// should not apply
+	c2_lptr_t *transparent_clipping_blacklist;
 } options_t;
 
 extern const char *const BACKEND_STRS[NUM_BKEND + 1];

src/config_libconfig.c

@@ -452,6 +452,9 @@ char *parse_config_libconfig(options_t *opt, const char *config_file, bool *shad
 	lcfg_lookup_bool(&cfg, "no-ewmh-fullscreen", &opt->no_ewmh_fullscreen);
 	// --transparent-clipping
 	lcfg_lookup_bool(&cfg, "transparent-clipping", &opt->transparent_clipping);
+	// --transparent-clipping-exclude
+	parse_cfg_condlst(&cfg, &opt->transparent_clipping_blacklist,
+	                  "transparent-clipping-exclude");
 	// --shadow-exclude
 	parse_cfg_condlst(&cfg, &opt->shadow_blacklist, "shadow-exclude");
 	// --clip-shadow-above

src/options.c

@@ -348,6 +348,11 @@ static void usage(const char *argv0, int ret) {
 	    "  Make transparent windows clip other windows like non-transparent windows\n"
 	    "  do, instead of blending on top of them\n"
 	    "\n"
+	    "--transparent-clipping-exclude condition\n"
+	    "  Specify a list of conditions of windows that should never have\n"
+	    "  transparent clipping applied. Useful for screenshot tools, where you\n"
+	    "  need to be able to see through transparent parts of the window.\n"
+	    "\n"
 	    "--window-shader-fg shader\n"
 	    "  Specify GLSL fragment shader path for rendering window contents. Does\n"
 	    "  not work when `--legacy-backends` is enabled.\n"
@@ -455,6 +460,7 @@ static const struct option longopts[] = {
     {"clip-shadow-above", required_argument, NULL, 335},
     {"window-shader-fg", required_argument, NULL, 336},
     {"window-shader-fg-rule", required_argument, NULL, 337},
+    {"transparent-clipping-exclude", required_argument, NULL, 338},
     {"legacy-backends", no_argument, NULL, 733},
     {"monitor-repaint", no_argument, NULL, 800},
     {"diagnostics", no_argument, NULL, 801},
@@ -823,6 +829,11 @@ bool get_cfg(options_t *opt, int argc, char *const *argv, bool shadow_enable,
 			}
 			break;
 		}
+		case 338: {
+			// --transparent-clipping-exclude
+			condlst_add(&opt->transparent_clipping_blacklist, optarg);
+			break;
+		}
 		case 321: {
 			enum log_level tmp_level = string_to_log_level(optarg);
 			if (tmp_level == LOG_LEVEL_INVALID) {

src/picom.c

@@ -831,7 +831,7 @@ paint_preprocess(session_t *ps, bool *fade_running, bool *animation) {
 		// we add the window region to the ignored region
 		// Otherwise last_reg_ignore shouldn't change
 		if ((w->mode != WMODE_TRANS && !ps->o.force_win_blend) ||
-		    ps->o.transparent_clipping) {
+		    (ps->o.transparent_clipping && !w->transparent_clipping_excluded)) {
 			// w->mode == WMODE_SOLID or WMODE_FRAME_TRANS
 			region_t *tmp = rc_region_new();
 			if (w->mode == WMODE_SOLID) {

src/win.c

@@ -1225,6 +1225,9 @@ void win_on_factor_change(session_t *ps, struct managed_win *w) {
 
 	w->fade_excluded = c2_match(ps, w, ps->o.fade_blacklist, NULL);
 
+	w->transparent_clipping_excluded =
+	    c2_match(ps, w, ps->o.transparent_clipping_blacklist, NULL);
+
 	win_update_opacity_target(ps, w);
 
 	w->reg_ignore_valid = false;
@@ -1567,6 +1570,7 @@ struct win *fill_win(session_t *ps, struct win *w) {
 	    .rounded_corners = false,
 	    .paint_excluded = false,
 	    .fade_excluded = false,
+	    .transparent_clipping_excluded = false,
 	    .unredir_if_possible_excluded = false,
 	    .prop_shadow = -1,
 	    // following 4 are set in win_mark_client

src/win.h

@@ -232,6 +232,9 @@ struct managed_win {
 	/// Whether fading is excluded by the rules. Calculated.
 	bool fade_excluded;
 
+	/// Whether transparent clipping is excluded by the rules.
+	bool transparent_clipping_excluded;
+
 	// Frame-opacity-related members
 	/// Current window frame opacity. Affected by window opacity.
 	double frame_opacity;