Add support for new blur method `dual_kawase` [WIP]

**Work-in-Progress**

Add `dual_kawase` to configuration and argument parsing. Allow `kawase`
for backward compatibility. Add `--blur-strength` parameter for
blur-method `dual_kawase`.

Update documentation to reflect the new blur-method and parameters.

man/picom.1.asciidoc

@@ -166,7 +166,7 @@ OPTIONS
 *--detect-client-leader*::
 	Use 'WM_CLIENT_LEADER' to group windows, and consider windows in the same group focused at the same time. 'WM_TRANSIENT_FOR' has higher priority if *--detect-transient* is enabled, too.
 
-*--blur-method*, *--blur-size*, *--blur-deviation*::
+*--blur-method*, *--blur-size*, *--blur-deviation*, *--blur-strength*::
 	Parameters for background blurring, see the *BLUR* section for more information.
 
 *--blur-background*::
@@ -397,8 +397,8 @@ Available options of the 'blur' section are: ::
 
   *method*:::
     A string. Controls the blur method. Corresponds to the *--blur-method* command line option. Available choices are:
-      'none' to disable blurring; 'gaussian' for gaussian blur; 'box' for box blur; 'kernel' for convolution blur with a custom kernel.
-    Note: 'gaussian' and 'box' blur methods are only supported by the experimental backends.
+      'none' to disable blurring; 'gaussian' for gaussian blur; 'box' for box blur; 'kernel' for convolution blur with a custom kernel; 'dual_kawase' for dual-filter kawase blur.
+    Note: 'gaussian', 'box' and 'dual_kawase' blur methods are only supported by the experimental backends.
     (default: none)
 
   *size*:::
@@ -407,6 +407,9 @@ Available options of the 'blur' section are: ::
   *deviation*:::
     A floating point number. The standard deviation for the 'gaussian' blur method. Corresponds to the *--blur-deviation* command line option (default: 0.84089642).
 
+  *strength*:::
+    An integer in the range 0-20. The strength of the 'dual_kawase' blur method. Corresponds to the *--blur-strength* command line option. If set to zero, the value requested by *--blur-size* is approximated (default: 5).
+
   *kernel*:::
     A string. The kernel to use for the 'kernel' blur method, specified in the same format as the *--blur-kerns* option. Corresponds to the *--blur-kerns* command line option.
 

picom.sample.conf

@@ -143,6 +143,8 @@ focus-exclude = [ "class_g = 'Cairo-clock'" ];
 # blur-size = 12
 #
 # blur-deviation = false
+#
+# blur-strength = 5
 
 # Blur background of semi-transparent / ARGB windows. 
 # Bad in performance, with driver-dependent behavior. 

src/backend/backend.h

@@ -5,8 +5,8 @@
 
 #include <stdbool.h>
 
-#include "config.h"
 #include "compiler.h"
+#include "config.h"
 #include "driver.h"
 #include "kernel.h"
 #include "region.h"
@@ -65,6 +65,11 @@ struct kernel_blur_args {
 	int kernel_count;
 };
 
+struct dual_kawase_blur_args {
+	int size;
+	int strength;
+};
+
 struct backend_operations {
 	// ===========    Initialization    ===========
 

src/backend/gl/gl_common.c

@@ -977,6 +977,12 @@ void *gl_create_blur_context(backend_t *base, enum blur_method method, void *arg
 		return ctx;
 	}
 
+	if (method == BLUR_METHOD_DUAL_KAWASE) {
+		log_warn("Blur method 'dual_kawase' is not yet implemented.");
+		ctx->method = BLUR_METHOD_NONE;
+		return ctx;
+	}
+
 	int nkernels;
 	ctx->method = BLUR_METHOD_KERNEL;
 	if (method == BLUR_METHOD_KERNEL) {

src/backend/xrender/xrender.c

@@ -507,6 +507,12 @@ void *create_blur_context(backend_t *base attr_unused, enum blur_method method,
 		ret->method = BLUR_METHOD_NONE;
 		return ret;
 	}
+	if (method == BLUR_METHOD_DUAL_KAWASE) {
+		log_warn("Blur method 'dual_kawase' is not compatible with the 'xrender' "
+		         "backend.");
+		ret->method = BLUR_METHOD_NONE;
+		return ret;
+	}
 
 	ret->method = BLUR_METHOD_KERNEL;
 	struct conv **kernels;

src/config.c

@@ -88,6 +88,13 @@ enum blur_method parse_blur_method(const char *src) {
 		return BLUR_METHOD_BOX;
 	} else if (strcmp(src, "gaussian") == 0) {
 		return BLUR_METHOD_GAUSSIAN;
+	} else if (strcmp(src, "dual_kawase") == 0) {
+		return BLUR_METHOD_DUAL_KAWASE;
+	} else if (strcmp(src, "kawase") == 0) {
+		log_warn("Blur method 'kawase' has been renamed to 'dual_kawase'. "
+		         "Interpreted as 'dual_kawase', but this will stop working "
+		         "soon.");
+		return BLUR_METHOD_DUAL_KAWASE;
 	} else if (strcmp(src, "none") == 0) {
 		return BLUR_METHOD_NONE;
 	}
@@ -542,6 +549,7 @@ char *parse_config(options_t *opt, const char *config_file, bool *shadow_enable,
 	    .blur_method = BLUR_METHOD_NONE,
 	    .blur_radius = 3,
 	    .blur_deviation = 0.84089642,
+	    .blur_strength = 5,
 	    .blur_background_frame = false,
 	    .blur_background_fixed = false,
 	    .blur_background_blacklist = NULL,

src/config.h

@@ -23,8 +23,8 @@
 #include "kernel.h"
 #include "log.h"
 #include "region.h"
-#include "win_defs.h"
 #include "types.h"
+#include "win_defs.h"
 
 typedef struct session session_t;
 
@@ -60,6 +60,7 @@ enum blur_method {
 	BLUR_METHOD_KERNEL,
 	BLUR_METHOD_BOX,
 	BLUR_METHOD_GAUSSIAN,
+	BLUR_METHOD_DUAL_KAWASE,
 	BLUR_METHOD_INVALID,
 };
 
@@ -189,6 +190,8 @@ typedef struct options {
 	int blur_radius;
 	// Standard deviation for the gaussian blur
 	double blur_deviation;
+	// Strength of the dual_kawase blur
+	int blur_strength;
 	/// Whether to blur background when the window frame is not opaque.
 	/// Implies blur_background.
 	bool blur_background_frame;

src/config_libconfig.c

@@ -530,6 +530,8 @@ char *parse_config_libconfig(options_t *opt, const char *config_file, bool *shad
 	config_lookup_int(&cfg, "blur-size", &opt->blur_radius);
 	// --blur-deviation
 	config_lookup_float(&cfg, "blur-deviation", &opt->blur_deviation);
+	// --blur-strength
+	config_lookup_int(&cfg, "blur-strength", &opt->blur_strength);
 	// --blur-background
 	if (config_lookup_bool(&cfg, "blur-background", &ival) && ival) {
 		if (opt->blur_method == BLUR_METHOD_NONE) {
@@ -640,6 +642,7 @@ char *parse_config_libconfig(options_t *opt, const char *config_file, bool *shad
 		}
 
 		config_setting_lookup_float(blur_cfg, "deviation", &opt->blur_deviation);
+		config_setting_lookup_int(blur_cfg, "strength", &opt->blur_strength);
 	}
 
 	// Wintype settings

src/options.c

@@ -212,6 +212,9 @@ static void usage(const char *argv0, int ret) {
 	    "--blur-deviation\n"
 	    "  The standard deviation for the 'gaussian' blur method.\n"
 	    "\n"
+	    "--blur-strength\n"
+	    "  The strength level of the 'dual_kawase' blur method.\n"
+	    "\n"
 	    "--blur-background\n"
 	    "  Blur background of semi-transparent / ARGB windows. Bad in\n"
 	    "  performance. The switch name may change without prior\n"
@@ -435,7 +438,8 @@ static const struct option longopts[] = {
     {"blur-method", required_argument, NULL, 328},
     {"blur-size", required_argument, NULL, 329},
     {"blur-deviation", required_argument, NULL, 330},
-    {"shadow-color", required_argument, NULL, 331},
+    {"blur-strength", required_argument, NULL, 331},
+    {"shadow-color", required_argument, NULL, 332},
     {"experimental-backends", no_argument, NULL, 733},
     {"monitor-repaint", no_argument, NULL, 800},
     {"diagnostics", no_argument, NULL, 801},
@@ -605,7 +609,7 @@ bool get_cfg(options_t *opt, int argc, char *const *argv, bool shadow_enable,
 		case 256:
 			// --config
 			break;
-		case 331:;
+		case 332:;
 			// --shadow-color
 			struct color rgb;
 			rgb = hex_to_rgb(optarg);
@@ -844,6 +848,10 @@ bool get_cfg(options_t *opt, int argc, char *const *argv, bool shadow_enable,
 			// --blur-deviation
 			opt->blur_deviation = atof(optarg);
 			break;
+		case 331:
+			// --blur-strength
+			opt->blur_strength = atoi(optarg);
+			break;
 
 		P_CASEBOOL(733, experimental_backends);
 		P_CASEBOOL(800, monitor_repaint);
@@ -933,6 +941,20 @@ bool get_cfg(options_t *opt, int argc, char *const *argv, bool shadow_enable,
 		CHECK(opt->blur_kernel_count);
 	}
 
+	// Sanitize parameters for dual-filter kawase blur
+	if (opt->blur_method == BLUR_METHOD_DUAL_KAWASE) {
+		if (opt->blur_strength <= 0 && opt->blur_radius > 500) {
+			log_warn("Blur radius >500 not supported by dual_kawase method, "
+			         "capping to 500.");
+			opt->blur_radius = 500;
+		}
+		if (opt->blur_strength > 20) {
+			log_warn("Blur strength >20 not supported by dual_kawase method, "
+			         "capping to 20.");
+			opt->blur_strength = 20;
+		}
+	}
+
 	if (opt->resize_damage < 0) {
 		log_warn("Negative --resize-damage will not work correctly.");
 	}

src/picom.c

@@ -431,6 +431,7 @@ static bool initialize_blur(session_t *ps) {
 	struct kernel_blur_args kargs;
 	struct gaussian_blur_args gargs;
 	struct box_blur_args bargs;
+	struct dual_kawase_blur_args dkargs;
 
 	void *args = NULL;
 	switch (ps->o.blur_method) {
@@ -448,6 +449,11 @@ static bool initialize_blur(session_t *ps) {
 		gargs.deviation = ps->o.blur_deviation;
 		args = (void *)&gargs;
 		break;
+	case BLUR_METHOD_DUAL_KAWASE:
+		dkargs.size = ps->o.blur_radius;
+		dkargs.strength = ps->o.blur_strength;
+		args = (void *)&dkargs;
+		break;
 	default: return true;
 	}