Fix initial rendering and mouse scaling

This commit adds first-run damage marking to ensure screen content is
rendered on startup instead of remaining blank until user interaction.
For mouse coordinate scaling, this scales EV_ABS coordinates from the
device range (0-32767) to actual screen resolution for correct cursor
positioning in touchscreen environments.

Close #62

Author: jserv

backend/fbdev.c

@@ -201,6 +201,16 @@ static bool twin_fbdev_work(void *closure)
     twin_fbdev_t *tx = PRIV(closure);
     twin_screen_t *screen = SCREEN(closure);
 
+    /* Mark entire screen as damaged on first run to ensure initial rendering.
+     * This is necessary because the screen content is not automatically
+     * rendered when the application starts.
+     */
+    static bool first_run = true;
+    if (first_run) {
+        first_run = false;
+        twin_screen_damage(screen, 0, 0, screen->width, screen->height);
+    }
+
     if (tx->vt_active && (tx->fb_base != MAP_FAILED)) {
         /* Unmap the fbdev */
         munmap(tx->fb_base, tx->fb_len);

backend/linux_input.c

@@ -79,16 +79,21 @@ static void twin_linux_input_events(struct input_event *ev,
         }
         break;
     case EV_ABS:
+        /* Scale absolute coordinates to screen resolution.
+         * Most touchscreens and absolute pointing devices report coordinates
+         * in the range 0-32767. We need to scale these to match the screen
+         * dimensions for correct cursor positioning.
+         */
         if (ev->code == ABS_X) {
-            tm->x = ev->value;
+            tm->x = ((int64_t) ev->value * tm->screen->width) / 32767;
             check_mouse_bounds(tm);
             tev.kind = TwinEventMotion;
             tev.u.pointer.screen_x = tm->x;
             tev.u.pointer.screen_y = tm->y;
             tev.u.pointer.button = tm->btns;
             twin_screen_dispatch(tm->screen, &tev);
         } else if (ev->code == ABS_Y) {
-            tm->y = ev->value;
+            tm->y = ((int64_t) ev->value * tm->screen->height) / 32767;
             check_mouse_bounds(tm);
             tev.kind = TwinEventMotion;
             tev.u.pointer.screen_x = tm->x;