fractional-scale: post error on taken fs objects

fixes #3735

2 files changed, 14 insertions, 1 deletions

diff --git a/src/protocols/FractionalScale.cpp b/src/protocols/FractionalScale.cpp
index f659a63a..19e60295 100644
--- a/src/protocols/FractionalScale.cpp
+++ b/src/protocols/FractionalScale.cpp
@@ -76,7 +76,13 @@ static void handleAddonDestroy(wl_resource* resource) {
 
 void CFractionalScaleProtocolManager::getFractionalScale(wl_client* client, wl_resource* resource, uint32_t id, wl_resource* surface) {
     const auto PSURFACE = wlr_surface_from_resource(surface);
-    const auto PADDON   = getAddonForSurface(PSURFACE);
+
+    if (addonExists(PSURFACE)) {
+        wl_resource_post_error(resource, WP_FRACTIONAL_SCALE_MANAGER_V1_ERROR_FRACTIONAL_SCALE_EXISTS, "Fractional scale exists.");
+        return;
+    }
+
+    const auto PADDON = getAddonForSurface(PSURFACE);
 
     PADDON->pResource = wl_resource_create(client, &wp_fractional_scale_v1_interface, wl_resource_get_version(resource), id);
     wl_resource_set_implementation(PADDON->pResource, &fractionalScaleAddonImpl, PADDON, handleAddonDestroy);
@@ -84,6 +90,12 @@ void CFractionalScaleProtocolManager::getFractionalScale(wl_client* client, wl_r
     wp_fractional_scale_v1_send_preferred_scale(PADDON->pResource, (uint32_t)std::round(PADDON->preferredScale * 120.0));
 }
 
+bool CFractionalScaleProtocolManager::addonExists(wlr_surface* surface) {
+    const auto IT = std::find_if(m_vFractionalScaleAddons.begin(), m_vFractionalScaleAddons.end(), [&](const auto& other) { return other->pSurface == surface; });
+
+    return IT != m_vFractionalScaleAddons.end();
+}
+
 SFractionalScaleAddon* CFractionalScaleProtocolManager::getAddonForSurface(wlr_surface* surface) {
     const auto IT = std::find_if(m_vFractionalScaleAddons.begin(), m_vFractionalScaleAddons.end(), [&](const auto& other) { return other->pSurface == surface; });
 
diff --git a/src/protocols/FractionalScale.hpp b/src/protocols/FractionalScale.hpp
index 71b2c858..99696319 100644
--- a/src/protocols/FractionalScale.hpp
+++ b/src/protocols/FractionalScale.hpp
@@ -30,6 +30,7 @@ class CFractionalScaleProtocolManager {
 
   private:
     SFractionalScaleAddon*                              getAddonForSurface(wlr_surface*);
+    bool                                                addonExists(wlr_surface*);
 
     std::vector<std::unique_ptr<SFractionalScaleAddon>> m_vFractionalScaleAddons;