Reduce cursor latency by rendering to VNC framebuf

Previously, cursor movement was handled by passing pointer events into
twin screen, and then calculated the damage region for the cursor's new
position and transmitted it to the VNC framebuffer. This process
introduced latency in cursor display due to the multiple steps involved.
To address this delay, the cursor is now rendered directly within the
VNC framebuffer by leveraging neatvnc's internal cursor API. This change
bypasses the intermediate steps and provides a smoother and more
responsive cursor movement experience in the VNC backend.

Makefile

@@ -113,6 +113,7 @@ endif
 ifeq ($(CONFIG_BACKEND_VNC), y)
 BACKEND = vnc
 libtwin.a_files-y += backend/vnc.c
+libtwin.a_files-y += src/cursor.c
 libtwin.a_cflags-y += $(shell pkg-config --cflags neatvnc aml pixman-1)
 TARGET_LIBS += $(shell pkg-config --libs neatvnc aml pixman-1)
 endif

backend/vnc.c

@@ -47,6 +47,9 @@ typedef struct {
     enum nvnc_button_mask prev_button;
 } twin_peer_t;
 
+#define CURSOR_WIDTH 14
+#define CURSOR_HEIGHT 20
+
 static void _twin_vnc_put_begin(twin_coord_t left,
                                 twin_coord_t top,
                                 twin_coord_t right,
@@ -147,6 +150,21 @@ static void _twin_vnc_pointer_event(struct nvnc_client *client,
     twin_screen_dispatch(tx->screen, &tev);
 }
 
+static struct nvnc_fb *_twin_vnc_create_cursor()
+{
+    struct nvnc_fb *fb = nvnc_fb_new(CURSOR_WIDTH, CURSOR_HEIGHT,
+                                     DRM_FORMAT_ARGB8888, CURSOR_WIDTH);
+    uint32_t *pixels = nvnc_fb_get_addr(fb);
+    for (int i = 0; i < CURSOR_WIDTH * CURSOR_HEIGHT; i++) {
+        uint32_t a = _twin_cursor_default[i * 4];
+        uint32_t r = _twin_cursor_default[i * 4 + 1];
+        uint32_t g = _twin_cursor_default[i * 4 + 2];
+        uint32_t b = _twin_cursor_default[i * 4 + 3];
+        pixels[i] = (a << 24) | (r << 16) | (g << 8) | b;
+    }
+    return fb;
+}
+
 twin_context_t *twin_vnc_init(int width, int height)
 {
     twin_context_t *ctx = calloc(1, sizeof(twin_context_t));
@@ -200,6 +218,10 @@ twin_context_t *twin_vnc_init(int width, int height)
     nvnc_set_pointer_fn(tx->server, _twin_vnc_pointer_event);
     nvnc_set_new_client_fn(tx->server, _twin_vnc_new_client);
     nvnc_set_userdata(tx->server, tx, NULL);
+    struct nvnc_fb *cursor = _twin_vnc_create_cursor();
+    nvnc_set_cursor(tx->server, cursor, CURSOR_WIDTH, CURSOR_HEIGHT, 0, 0,
+                    true);
+    nvnc_fb_unref(cursor);
 
     ctx->screen = twin_screen_create(width, height, _twin_vnc_put_begin,
                                      _twin_vnc_put_span, ctx);

configs/Kconfig

@@ -41,6 +41,7 @@ comment "Logging is disabled"
 config CURSOR
     bool "Manipulate cursor"
     default n
+    depends on !BACKEND_VNC
 
 endmenu
 

include/twin.h

@@ -613,6 +613,8 @@ void twin_path_convolve(twin_path_t *dest,
  * cursor.c
  */
 
+extern const uint8_t _twin_cursor_default[];
+
 twin_pixmap_t *twin_make_cursor(int *hx, int *hy);
 
 /*

src/cursor.c

@@ -9,7 +9,7 @@
 #include <stddef.h>
 #include <twin.h>
 
-static const uint8_t _twin_cursor_default[] = {
+const uint8_t _twin_cursor_default[] = {
     0x19, 0x19, 0x19, 0xb8, 0x1e, 0x1e, 0x1e, 0xc8, 0x00, 0x00, 0x00, 0x13,
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x00,
     0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,