Create utility function for checking buffer damage

Makefile

@@ -6,6 +6,7 @@ SOURCES := \
 	src/vec.c \
 	src/zrle.c \
 	src/pixels.c \
+	src/damage.c \
 
 include common.mk
 

include/neatvnc.h

@@ -53,6 +53,7 @@ typedef void (*nvnc_fb_req_fn)(struct nvnc_client*, bool is_incremental,
                                uint16_t x, uint16_t y,
                                uint16_t width, uint16_t height);
 typedef void (*nvnc_client_fn)(struct nvnc_client*);
+typedef void (*nvnc_damage_fn)(struct pixman_region16 *damage, void *userdata);
 
 struct nvnc *nvnc_open(const char *addr, uint16_t port);
 void nvnc_close(struct nvnc *self);
@@ -80,3 +81,13 @@ void nvnc_set_client_cleanup_fn(struct nvnc_client *self, nvnc_client_fn fn);
  */
 int nvnc_update_fb(struct nvnc *self, const struct nvnc_fb* fb,
                    const struct pixman_region16* region);
+
+/*
+ * Find the regions that differ between fb0 and fb1. Regions outside the hinted
+ * rectangle region are not guaranteed to be checked.
+ *
+ * This is a utility function that may be used to reduce network traffic.
+ */
+int nvnc_check_damage(const struct nvnc_fb *fb0, const struct nvnc_fb *fb1,
+		      int x_hint, int y_hint, int width_hint, int height_hint,
+		      nvnc_damage_fn on_check_done, void *userdata);

src/damage.c

@@ -0,0 +1,156 @@
+#include "neatvnc.h"
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <pixman.h>
+#include <string.h>
+#include <sys/param.h>
+#include <libdrm/drm_fourcc.h>
+#include <uv.h>
+#include <assert.h>
+
+#define EXPORT __attribute__((visibility("default")))
+#define ALIGN_DOWN(a, b) (((a) / (b)) * (b))
+
+struct damage_check {
+	uv_work_t work;
+	const struct nvnc_fb *fb0;
+	const struct nvnc_fb *fb1;
+	int x_hint;
+	int y_hint;
+	int width_hint;
+	int height_hint;
+	nvnc_damage_fn on_done;
+	struct pixman_region16 damage;
+	void *userdata;
+};
+
+static bool fbs_are_compatible(const struct nvnc_fb *fb0,
+			       const struct nvnc_fb *fb1)
+{
+	return fb0->fourcc_format == fb1->fourcc_format
+	    && fb0->fourcc_modifier == fb1->fourcc_modifier
+	    && fb0->nvnc_modifier == fb1->nvnc_modifier
+	    && fb0->width == fb1->width
+	    && fb0->height == fb1->height;
+}
+
+static inline bool are_tiles_equal(const uint32_t* a, const uint32_t* b,
+				   int stride, int width, int height)
+{
+	for (int y = 0; y < height; ++y)
+		if (memcmp(a + y * stride, b + y * stride, width * 4) != 0)
+			return false;
+
+	return true;
+}
+
+#define TILE_SIDE_LENGTH 32
+int check_damage_linear(struct pixman_region16 *damage,
+			const struct nvnc_fb *fb0, const struct nvnc_fb *fb1,
+			int x_hint, int y_hint, int width_hint, int height_hint)
+{
+	uint32_t *b0 = fb0->addr;
+	uint32_t *b1 = fb1->addr;
+
+	int width = fb0->width;
+	int height = fb0->height;
+
+	assert(x_hint + width_hint <= width);
+	assert(y_hint + height_hint <= height);
+
+	int x_start = ALIGN_DOWN(x_hint, TILE_SIDE_LENGTH);
+	int y_start = ALIGN_DOWN(y_hint, TILE_SIDE_LENGTH);
+	
+	for (int y = y_start; y < y_start + height_hint;
+	     y += TILE_SIDE_LENGTH) {
+		int tile_height = MIN(TILE_SIDE_LENGTH, height - y);
+
+		for (int x = x_start; x < x_start + width_hint;
+		     x += TILE_SIDE_LENGTH) {
+			int tile_width = MIN(TILE_SIDE_LENGTH, width - x);
+
+			if (are_tiles_equal(b0 + x + y * width,
+					    b1 + x + y * width,
+					    width, tile_width, tile_height))
+				continue;
+
+			pixman_region_union_rect(damage, damage, x, y,
+						 tile_width, tile_height);
+		}
+	}
+
+	return 0;
+}
+#undef TILE_SIDE_LENGTH
+
+void do_damage_check_linear(uv_work_t *work)
+{
+	struct damage_check *check = (void*)work;
+
+	check_damage_linear(&check->damage, check->fb0, check->fb1,
+			    check->x_hint, check->y_hint,
+			    check->width_hint, check->height_hint);
+}
+
+void on_damage_check_done_linear(uv_work_t *work, int status)
+{
+	(void)status;
+
+	struct damage_check *check = (void*)work;
+
+	check->on_done(&check->damage, check->userdata);
+
+	pixman_region_fini(&check->damage);
+	free(check);
+}
+
+int check_damage_linear_threaded(const struct nvnc_fb *fb0,
+				 const struct nvnc_fb *fb1,
+				 int x_hint, int y_hint,
+				 int width_hint, int height_hint,
+				 nvnc_damage_fn on_check_done,
+				 void *userdata)
+{
+	struct damage_check *work = calloc(1, sizeof(*work));
+	if (!work)
+		return -1;
+
+	work->on_done = on_check_done;
+	work->userdata = userdata;
+	work->fb0 = fb0;
+	work->fb1 = fb1;
+	work->x_hint = x_hint;
+	work->y_hint = y_hint;
+	work->width_hint = width_hint;
+	work->height_hint = height_hint;
+	pixman_region_init(&work->damage);
+
+	/* TODO: Spread the work into more tasks */
+	int rc = uv_queue_work(uv_default_loop(), &work->work,
+			       do_damage_check_linear,
+			       on_damage_check_done_linear);
+	if (rc < 0)
+		free(work);
+
+	return rc;
+}
+
+EXPORT
+int nvnc_check_damage(const struct nvnc_fb *fb0, const struct nvnc_fb *fb1,
+		      int x_hint, int y_hint, int width_hint, int height_hint,
+		      nvnc_damage_fn on_check_done, void *userdata)
+{
+	if (!fbs_are_compatible(fb0, fb1))
+		return -1;
+
+	switch (fb0->fourcc_modifier) {
+	case DRM_FORMAT_MOD_LINEAR:
+		return check_damage_linear_threaded(fb0, fb1, x_hint, y_hint,
+						    width_hint, height_hint,
+						    on_check_done, userdata);
+	}
+
+	return -1;
+}