backend: give backends more flexibility regarding shadow creation

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/backend.h

@@ -16,6 +16,8 @@
 typedef struct session session_t;
 struct managed_win;
 
+struct backend_shadow_context;
+
 struct ev_loop;
 struct backend_operations;
 
@@ -213,10 +215,24 @@ struct backend_operations {
 	void *(*bind_pixmap)(backend_t *backend_data, xcb_pixmap_t pixmap,
 	                     struct xvisual_info fmt, bool owned);
 
+	struct backend_shadow_context *(*create_shadow_context)(backend_t *backend_data,
+	                                                        double radius);
+	void (*destroy_shadow_context)(backend_t *backend_data,
+	                               struct backend_shadow_context *ctx);
+
 	/// Create a shadow image based on the parameters
 	/// Default implementation: default_backend_render_shadow
+	///
+	/// Required.
 	void *(*render_shadow)(backend_t *backend_data, int width, int height,
-	                       const conv *kernel, double r, double g, double b, double a);
+	                       struct backend_shadow_context *ctx, struct color color);
+
+	/// Create a shadow by blurring a mask. `size` is the size of the blur. The
+	/// backend can use whichever blur method is the fastest.
+	///
+	/// Optional.
+	void *(*shadow_from_mask)(backend_t *backend_data, void *mask,
+	                          struct backend_shadow_context *ctx, struct color color);
 
 	/// Create a mask image from region `reg`. This region can be used to create
 	/// shadow, or used as a mask for composing. When used as a mask, it should mask

src/backend/backend_common.c

@@ -291,16 +291,16 @@ shadow_picture_err:
 	return false;
 }
 
-void *
-default_backend_render_shadow(backend_t *backend_data, int width, int height,
-                              const conv *kernel, double r, double g, double b, double a) {
-	xcb_pixmap_t shadow_pixel = solid_picture(backend_data->c, backend_data->root,
-	                                          true, 1, r, g, b),
+void *default_backend_render_shadow(backend_t *backend_data, int width, int height,
+                                    struct backend_shadow_context *sctx, struct color color) {
+	const conv *kernel = (void *)sctx;
+	xcb_pixmap_t shadow_pixel = solid_picture(backend_data->c, backend_data->root, true,
+	                                          1, color.red, color.green, color.blue),
 	             shadow = XCB_NONE;
 	xcb_render_picture_t pict = XCB_NONE;
 
-	if (!build_shadow(backend_data->c, backend_data->root, a, width, height, kernel,
-	                  shadow_pixel, &shadow, &pict)) {
+	if (!build_shadow(backend_data->c, backend_data->root, color.alpha, width, height,
+	                  kernel, shadow_pixel, &shadow, &pict)) {
 		return NULL;
 	}
 
@@ -311,6 +311,19 @@ default_backend_render_shadow(backend_t *backend_data, int width, int height,
 	return ret;
 }
 
+struct backend_shadow_context *
+default_create_shadow_context(backend_t *backend_data attr_unused, double radius) {
+	auto ret =
+	    (struct backend_shadow_context *)gaussian_kernel_autodetect_deviation(radius);
+	sum_kernel_preprocess((conv *)ret);
+	return ret;
+}
+
+void default_destroy_shadow_context(backend_t *backend_data attr_unused,
+                                    struct backend_shadow_context *sctx) {
+	free_conv((conv *)sctx);
+}
+
 static struct conv **generate_box_blur_kernel(struct box_blur_args *args, int *kernel_count) {
 	int r = args->size * 2 + 1;
 	assert(r > 0);

src/backend/backend_common.h

@@ -62,9 +62,13 @@ bool default_is_win_transparent(void *, win *, void *);
 /// caveat as `default_is_win_transparent` applies.
 bool default_is_frame_transparent(void *, win *, void *);
 
-void *
-default_backend_render_shadow(backend_t *backend_data, int width, int height,
-                              const conv *kernel, double r, double g, double b, double a);
+void *default_backend_render_shadow(backend_t *backend_data, int width, int height,
+                                    struct backend_shadow_context *sctx, struct color color);
+struct backend_shadow_context *
+default_create_shadow_context(backend_t *backend_data, double radius);
+
+void default_destroy_shadow_context(backend_t *backend_data,
+                                    struct backend_shadow_context *sctx);
 
 void init_backend_base(struct backend_base *base, session_t *ps);
 

src/backend/dummy/dummy.c

@@ -175,6 +175,8 @@ struct backend_operations dummy_ops = {
     .fill = dummy_fill,
     .blur = dummy_blur,
     .bind_pixmap = dummy_bind_pixmap,
+    .create_shadow_context = default_create_shadow_context,
+    .destroy_shadow_context = default_destroy_shadow_context,
     .render_shadow = default_backend_render_shadow,
     .make_mask = dummy_make_mask,
     .release_image = dummy_release_image,

src/backend/gl/glx.c

@@ -536,6 +536,8 @@ struct backend_operations glx_ops = {
     .is_image_transparent = default_is_image_transparent,
     .present = glx_present,
     .buffer_age = glx_buffer_age,
+    .create_shadow_context = default_create_shadow_context,
+    .destroy_shadow_context = default_destroy_shadow_context,
     .render_shadow = default_backend_render_shadow,
     .make_mask = gl_make_mask,
     .fill = gl_fill,

src/backend/xrender/xrender.c

@@ -968,6 +968,8 @@ struct backend_operations xrender_ops = {
     .fill = fill,
     .bind_pixmap = bind_pixmap,
     .release_image = release_image,
+    .create_shadow_context = default_create_shadow_context,
+    .destroy_shadow_context = default_destroy_shadow_context,
     .render_shadow = default_backend_render_shadow,
     .make_mask = make_mask,
     //.prepare_win = prepare_win,

src/common.h

@@ -300,8 +300,8 @@ typedef struct session {
 	xcb_render_picture_t cshadow_picture;
 	/// 1x1 white Picture.
 	xcb_render_picture_t white_picture;
-	/// Gaussian map of shadow.
-	struct conv *gaussian_map;
+	/// Backend shadow context.
+	struct backend_shadow_context *shadow_context;
 	// for shadow precomputation
 	/// A region in which shadow is not painted on.
 	region_t shadow_exclude_reg;

src/kernel.c

@@ -90,15 +90,20 @@ conv *gaussian_kernel(double r, int size) {
 /// Estimate the element of the sum of the first row in a gaussian kernel with standard
 /// deviation `r` and size `size`,
 static inline double estimate_first_row_sum(double size, double r) {
+	// `factor` is integral of gaussian from -size to size
 	double factor = erf(size / r / sqrt(2));
+	// `a` is gaussian at (size, 0)
 	double a = exp(-0.5 * size * size / (r * r)) / sqrt(2 * M_PI) / r;
+	// The sum of the whole kernel is normalized to 1, i.e. each element is divided by
+	// factor sqaured. So the sum of the first row is a * factor / factor^2 = a /
+	// factor
 	return a / factor;
 }
 
-/// Pick a suitable gaussian kernel radius for a given kernel size. The returned radius
-/// is the maximum possible radius (<= size*2) that satisfies no sum of the rows in
-/// the kernel are less than `row_limit` (up to certain precision).
-static inline double gaussian_kernel_std_for_size(int size, double row_limit) {
+/// Pick a suitable gaussian kernel standard deviation for a given kernel size. The
+/// returned radius is the maximum possible radius (<= size*2) that satisfies no sum of
+/// the rows in the kernel are less than `row_limit` (up to certain precision).
+static inline double gaussian_kernel_std_for_size(double size, double row_limit) {
 	assert(size > 0);
 	if (row_limit >= 1.0 / 2.0 / size) {
 		return size * 2;
@@ -121,9 +126,9 @@ static inline double gaussian_kernel_std_for_size(int size, double row_limit) {
 /// transparent, so the transition from shadow to the background is smooth.
 ///
 /// @param[in] shadow_radius the radius of the shadow
-conv *gaussian_kernel_autodetect_deviation(int shadow_radius) {
+conv *gaussian_kernel_autodetect_deviation(double shadow_radius) {
 	assert(shadow_radius >= 0);
-	int size = shadow_radius * 2 + 1;
+	int size = (int)(shadow_radius * 2 + 1);
 
 	if (shadow_radius == 0) {
 		return gaussian_kernel(0, size);

src/kernel.h

@@ -27,7 +27,7 @@ conv *gaussian_kernel(double r, int size);
 /// transparent.
 ///
 /// @param[in] shadow_radius the radius of the shadow
-conv *gaussian_kernel_autodetect_deviation(int shadow_radius);
+conv *gaussian_kernel_autodetect_deviation(double shadow_radius);
 
 /// preprocess kernels to make shadow generation faster
 /// shadow_sum[x*d+y] is the sum of the kernel from (0, 0) to (x, y), inclusive

src/picom.c

@@ -451,6 +451,11 @@ static void destroy_backend(session_t *ps) {
 			    ps->backend_data, ps->backend_blur_context);
 			ps->backend_blur_context = NULL;
 		}
+		if (ps->shadow_context) {
+			ps->backend_data->ops->destroy_shadow_context(ps->backend_data,
+			                                              ps->shadow_context);
+			ps->shadow_context = NULL;
+		}
 		ps->backend_data->ops->deinit(ps->backend_data);
 		ps->backend_data = NULL;
 	}
@@ -504,6 +509,12 @@ static bool initialize_backend(session_t *ps) {
 			return false;
 		}
 		ps->backend_data->ops = backend_list[ps->o.backend];
+		ps->shadow_context = ps->backend_data->ops->create_shadow_context(
+		    ps->backend_data, ps->o.shadow_radius);
+		if (!ps->shadow_context) {
+			log_fatal("Failed to initialize shadow context, aborting...");
+			goto err;
+		}
 
 		if (!initialize_blur(ps)) {
 			log_fatal("Failed to prepare for background blur, aborting...");
@@ -553,6 +564,11 @@ static bool initialize_backend(session_t *ps) {
 	// The old backends binds pixmap lazily, nothing to do here
 	return true;
 err:
+	if (ps->shadow_context) {
+		ps->backend_data->ops->destroy_shadow_context(ps->backend_data,
+		                                              ps->shadow_context);
+		ps->shadow_context = NULL;
+	}
 	ps->backend_data->ops->deinit(ps->backend_data);
 	ps->backend_data = NULL;
 	quit(ps);
@@ -1675,7 +1691,7 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 	    .black_picture = XCB_NONE,
 	    .cshadow_picture = XCB_NONE,
 	    .white_picture = XCB_NONE,
-	    .gaussian_map = NULL,
+	    .shadow_context = NULL,
 
 #ifdef CONFIG_VSYNC_DRM
 	    .drm_fd = -1,
@@ -1929,8 +1945,11 @@ static session_t *session_init(int argc, char **argv, Display *dpy,
 		}
 	}
 
-	ps->gaussian_map = gaussian_kernel_autodetect_deviation(ps->o.shadow_radius);
-	sum_kernel_preprocess(ps->gaussian_map);
+	if (ps->o.legacy_backends) {
+		ps->shadow_context =
+		    (void *)gaussian_kernel_autodetect_deviation(ps->o.shadow_radius);
+		sum_kernel_preprocess((conv *)ps->shadow_context);
+	}
 
 	rebuild_shadow_exclude_reg(ps);
 
@@ -2408,7 +2427,9 @@ static void session_destroy(session_t *ps) {
 	// Flush all events
 	x_sync(ps->c);
 	ev_io_stop(ps->loop, &ps->xiow);
-	free_conv(ps->gaussian_map);
+	if (ps->o.legacy_backends) {
+		free_conv((conv *)ps->shadow_context);
+	}
 	destroy_atoms(ps->atoms);
 
 #ifdef DEBUG_XRC

src/render.c

@@ -649,8 +649,9 @@ static bool get_root_tile(session_t *ps) {
 static void paint_root(session_t *ps, const region_t *reg_paint) {
 	// If there is no root tile pixmap, try getting one.
 	// If that fails, give up.
-	if (!ps->root_tile_paint.pixmap && !get_root_tile(ps))
+	if (!ps->root_tile_paint.pixmap && !get_root_tile(ps)) {
 		return;
+	}
 
 	paint_region(ps, NULL, 0, 0, ps->root_width, ps->root_height, 1.0, reg_paint,
 	             ps->root_tile_paint.pict);
@@ -669,7 +670,7 @@ static bool win_build_shadow(session_t *ps, struct managed_win *w, double opacit
 	xcb_render_picture_t shadow_picture = XCB_NONE, shadow_picture_argb = XCB_NONE;
 	xcb_gcontext_t gc = XCB_NONE;
 
-	shadow_image = make_shadow(ps->c, ps->gaussian_map, opacity, width, height);
+	shadow_image = make_shadow(ps->c, (conv *)ps->shadow_context, opacity, width, height);
 	if (!shadow_image) {
 		log_error("failed to make shadow");
 		return XCB_NONE;
@@ -689,8 +690,9 @@ static bool win_build_shadow(session_t *ps, struct managed_win *w, double opacit
 	    ps->c, XCB_PICT_STANDARD_A_8, shadow_pixmap, 0, NULL);
 	shadow_picture_argb = x_create_picture_with_standard_and_pixmap(
 	    ps->c, XCB_PICT_STANDARD_ARGB_32, shadow_pixmap_argb, 0, NULL);
-	if (!shadow_picture || !shadow_picture_argb)
+	if (!shadow_picture || !shadow_picture_argb) {
 		goto shadow_picture_err;
+	}
 
 	gc = x_new_id(ps->c);
 	xcb_create_gc(ps->c, gc, shadow_pixmap, 0, NULL);

src/win.c

@@ -346,11 +346,10 @@ static inline bool win_bind_pixmap(struct backend_base *b, struct managed_win *w
 }
 
 bool win_bind_shadow(struct backend_base *b, struct managed_win *w, struct color c,
-                     struct conv *kernel) {
+                     struct backend_shadow_context *sctx) {
 	assert(!w->shadow_image);
 	assert(w->shadow);
-	w->shadow_image = b->ops->render_shadow(b, w->widthb, w->heightb, kernel, c.red,
-	                                        c.green, c.blue, c.alpha);
+	w->shadow_image = b->ops->render_shadow(b, w->widthb, w->heightb, sctx, c);
 	if (!w->shadow_image) {
 		log_error("Failed to bind shadow image, shadow will be disabled for "
 		          "%#010x (%s)",
@@ -556,7 +555,7 @@ void win_process_image_flags(session_t *ps, struct managed_win *w) {
 				                               .green = ps->o.shadow_green,
 				                               .blue = ps->o.shadow_blue,
 				                               .alpha = ps->o.shadow_opacity},
-				                ps->gaussian_map);
+				                ps->shadow_context);
 			}
 		}
 

src/win.h

@@ -7,6 +7,8 @@
 #include <xcb/render.h>
 #include <xcb/xcb.h>
 
+#include <backend/backend.h>
+
 #include "uthash_extra.h"
 
 // FIXME shouldn't need this
@@ -289,7 +291,7 @@ void win_process_update_flags(session_t *ps, struct managed_win *w);
 void win_process_image_flags(session_t *ps, struct managed_win *w);
 /// Bind a shadow to the window, with color `c` and shadow kernel `kernel`
 bool win_bind_shadow(struct backend_base *b, struct managed_win *w, struct color c,
-                     struct conv *kernel);
+                     struct backend_shadow_context *kernel);
 
 /// Start the unmap of a window. We cannot unmap immediately since we might need to fade
 /// the window out.