Add dummy backend

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

src/backend/backend.c

@@ -10,13 +10,14 @@
 #include "region.h"
 #include "win.h"
 
-extern struct backend_operations xrender_ops;
+extern struct backend_operations xrender_ops, dummy_ops;
 #ifdef CONFIG_OPENGL
 extern struct backend_operations glx_ops;
 #endif
 
 struct backend_operations *backend_list[NUM_BKEND] = {
     [BKEND_XRENDER] = &xrender_ops,
+    [BKEND_DUMMY] = &dummy_ops,
 #ifdef CONFIG_OPENGL
     [BKEND_GLX] = &glx_ops,
 #endif

src/backend/backend.h

@@ -225,8 +225,10 @@ struct backend_operations {
 
 	// ===========         Hooks        ============
 	/// Let the backend hook into the event handling queue
+	/// Not implemented yet
 	void (*set_ready_callback)(backend_t *, backend_ready_callback_t cb);
 	/// Called right after compton has handled its events.
+	/// Not implemented yet
 	void (*handle_events)(backend_t *);
 	// ===========         Misc         ============
 	/// Return the driver that is been used by the backend

src/backend/dummy/dummy.c

@@ -0,0 +1,159 @@
+#include <uthash.h>
+#include <xcb/xcb.h>
+
+#include "backend/backend_common.h"
+#include "common.h"
+#include "compiler.h"
+#include "uthash_extra.h"
+#include "utils.h"
+
+struct dummy_image {
+	xcb_pixmap_t pixmap;
+	bool transparent;
+	int refcount;
+	UT_hash_handle hh;
+};
+
+struct dummy_data {
+	struct backend_base base;
+	struct dummy_image *images;
+};
+
+struct backend_base *dummy_init(struct session *ps attr_unused) {
+	return (struct backend_base *)ccalloc(1, struct dummy_data);
+}
+
+void dummy_deinit(struct backend_base *data) {
+	auto dummy = (struct dummy_data *)data;
+	HASH_ITER2(dummy->images, img) {
+		log_warn("Backend image for pixmap %#010x is not freed", img->pixmap);
+		HASH_DEL(dummy->images, img);
+		free(img);
+	}
+	free(dummy);
+}
+
+void dummy_compose(struct backend_base *base, void *image, int dst_x attr_unused,
+                   int dst_y attr_unused, const region_t *reg_paint attr_unused,
+                   const region_t *reg_visible attr_unused) {
+	auto dummy = (struct dummy_data *)base;
+	auto img = (struct dummy_image *)image;
+
+	struct dummy_image *tmp = NULL;
+	HASH_FIND_INT(dummy->images, &img->pixmap, tmp);
+	if (!tmp) {
+		log_warn("Composing with an invalid (possibly freed) image");
+	}
+}
+
+void dummy_fill(struct backend_base *backend_data attr_unused, struct color c attr_unused,
+                const region_t *clip attr_unused) {
+}
+
+bool dummy_blur(struct backend_base *backend_data attr_unused, double opacity attr_unused,
+                void *blur_ctx attr_unused, const region_t *reg_blur attr_unused,
+                const region_t *reg_visible attr_unused) {
+	return true;
+}
+
+void *dummy_bind_pixmap(struct backend_base *base, xcb_pixmap_t pixmap,
+                        struct xvisual_info fmt, bool owned attr_unused) {
+	auto dummy = (struct dummy_data *)base;
+	struct dummy_image *img = NULL;
+	HASH_FIND_INT(dummy->images, &pixmap, img);
+	if (img) {
+		img->refcount++;
+		return img;
+	}
+
+	img = ccalloc(1, struct dummy_image);
+	img->pixmap = pixmap;
+	img->transparent = fmt.alpha_size != 0;
+	img->refcount = 1;
+
+	HASH_ADD_INT(dummy->images, pixmap, img);
+	return (void *)img;
+}
+
+void dummy_release_image(backend_t *base, void *image) {
+	auto dummy = (struct dummy_data *)base;
+	auto img = (struct dummy_image *)image;
+	assert(img->refcount > 0);
+	img->refcount--;
+	if (img->refcount == 0) {
+		HASH_DEL(dummy->images, img);
+		free(img);
+	}
+}
+
+bool dummy_is_image_transparent(struct backend_base *base, void *image) {
+	auto dummy = (struct dummy_data *)base;
+	auto img = (struct dummy_image *)image;
+	struct dummy_image *tmp = NULL;
+	HASH_FIND_INT(dummy->images, &img->pixmap, tmp);
+	if (!tmp) {
+		log_warn("Using an invalid (possibly freed) image");
+	}
+	return img->transparent;
+}
+
+int dummy_buffer_age(struct backend_base *base attr_unused) {
+	return 2;
+}
+
+bool dummy_image_op(struct backend_base *base attr_unused, enum image_operations op attr_unused,
+                    void *image attr_unused, const region_t *reg_op attr_unused,
+                    const region_t *reg_visible attr_unused, void *args attr_unused) {
+	return true;
+}
+
+void *dummy_image_copy(struct backend_base *base, const void *image,
+                       const region_t *reg_visible attr_unused) {
+	auto dummy = (struct dummy_data *)base;
+	auto img = (struct dummy_image *)image;
+	struct dummy_image *tmp = NULL;
+	HASH_FIND_INT(dummy->images, &img->pixmap, tmp);
+	if (!tmp) {
+		log_warn("Using an invalid (possibly freed) image");
+	}
+	img->refcount++;
+	return img;
+}
+
+void *dummy_create_blur_context(struct backend_base *base attr_unused,
+                                enum blur_method method attr_unused, void *args attr_unused) {
+	static int dummy_context;
+	return &dummy_context;
+}
+
+void dummy_destroy_blur_context(struct backend_base *base attr_unused, void *ctx attr_unused) {
+
+}
+
+void dummy_get_blur_size(void *ctx attr_unused, int *width, int *height) {
+	// These numbers are arbitrary, to make sure the reisze_region code path is
+	// covered.
+	*width = 5;
+	*height = 5;
+}
+
+struct backend_operations dummy_ops = {
+    .init = dummy_init,
+    .deinit = dummy_deinit,
+    .compose = dummy_compose,
+    .fill = dummy_fill,
+    .blur = dummy_blur,
+    .bind_pixmap = dummy_bind_pixmap,
+    .render_shadow = default_backend_render_shadow,
+    .release_image = dummy_release_image,
+    .is_image_transparent = dummy_is_image_transparent,
+    .buffer_age = dummy_buffer_age,
+    .max_buffer_age = 5,
+
+    .image_op = dummy_image_op,
+    .copy = dummy_image_copy,
+    .create_blur_context = dummy_create_blur_context,
+    .destroy_blur_context = dummy_destroy_blur_context,
+    .get_blur_size = dummy_get_blur_size,
+
+};

src/backend/meson.build

@@ -1,5 +1,5 @@
 # enable xrender
-srcs += [ files('backend_common.c', 'xrender/xrender.c', 'backend.c', 'driver.c') ]
+srcs += [ files('backend_common.c', 'xrender/xrender.c', 'dummy/dummy.c', 'backend.c', 'driver.c') ]
 
 # enable opengl
 if get_option('opengl')

src/compton.c

@@ -80,9 +80,10 @@ const char *const WINTYPES[NUM_WINTYPES] = {
 };
 
 /// Names of backends.
-const char *const BACKEND_STRS[NUM_BKEND + 1] = {"xrender",              // BKEND_XRENDER
-                                                 "glx",                  // BKEND_GLX
-                                                 "xr_glx_hybrid",        // BKEND_XR_GLX_HYBRID
+const char *const BACKEND_STRS[] = {[BKEND_XRENDER] = "xrender",
+                                    [BKEND_GLX] = "glx",
+                                    [BKEND_XR_GLX_HYBRID] = "xr_glx_hybrid",
+                                    [BKEND_DUMMY] = "dummy",
                                     NULL};
 
 // === Global variables ===

src/config.h

@@ -34,6 +34,7 @@ enum backend {
 	BKEND_XRENDER,
 	BKEND_GLX,
 	BKEND_XR_GLX_HYBRID,
+	BKEND_DUMMY,
 	NUM_BKEND,
 };
 

src/render.c

@@ -1087,6 +1087,10 @@ static bool init_alpha_picts(session_t *ps) {
 }
 
 bool init_render(session_t *ps) {
+	if (ps->o.backend == BKEND_DUMMY) {
+		return false;
+	}
+
 	// Initialize OpenGL as early as possible
 #ifdef CONFIG_OPENGL
 	glxext_init(ps->dpy, ps->scr);