pointer/hw: rollback the swapchain on multiple renders without a commit

fixes the hack

2 files changed, 21 insertions, 6 deletions

diff --git a/src/managers/PointerManager.cpp b/src/managers/PointerManager.cpp
index 55bd0509..3b425688 100644
--- a/src/managers/PointerManager.cpp
+++ b/src/managers/PointerManager.cpp
@@ -24,6 +24,14 @@ CPointerManager::CPointerManager() {
             },
             nullptr);
     });
+
+    hooks.monitorPreRender = g_pHookSystem->hookDynamic("preRender", [this](void* self, SCallbackInfo& info, std::any data) {
+        auto state = stateFor(std::any_cast<CMonitor*>(data)->self.lock());
+        if (!state)
+            return;
+
+        state->cursorRendered = false;
+    });
 }
 
 void CPointerManager::lockSoftwareAll() {
@@ -373,10 +381,7 @@ SP<Aquamarine::IBuffer> CPointerManager::renderHWCursorBuffer(SP<CPointerManager
 
         auto options     = state->monitor->cursorSwapchain->currentOptions();
         options.size     = maxSize;
-        // TODO: this is a band-aid. If the current cursor image has not yet been committed (no rendering has yet been done)
-        // we should revert the swapchain and avoid rendering to the front buffer.
-        // as a band-aid, extend the swapchain to 3 as we sometimes double-render on a cursor shape change.
-        options.length   = 3;
+        options.length   = 2;
         options.scanout  = true;
         options.cursor   = true;
         options.multigpu = state->monitor->output->getBackend()->preferredAllocator()->drmFD() != g_pCompositor->m_iDRMFD;
@@ -389,6 +394,14 @@ SP<Aquamarine::IBuffer> CPointerManager::renderHWCursorBuffer(SP<CPointerManager
         }
     }
 
+    // if we already rendered the cursor, revert the swapchain to avoid rendering the cursor over
+    // the current front buffer
+    // this flag will be reset in the preRender hook, so when we commit this buffer to KMS
+    if (state->cursorRendered)
+        state->monitor->cursorSwapchain->rollback();
+
+    state->cursorRendered = true;
+
     auto buf = state->monitor->cursorSwapchain->next(nullptr);
     if (!buf) {
         Debug::log(TRACE, "Failed to acquire a buffer from the cursor swapchain");
diff --git a/src/managers/PointerManager.hpp b/src/managers/PointerManager.hpp
index cf4f1a94..4a4c4f61 100644
--- a/src/managers/PointerManager.hpp
+++ b/src/managers/PointerManager.hpp
@@ -163,8 +163,9 @@ class CPointerManager {
         int                     softwareLocks  = 0;
         bool                    hardwareFailed = false;
         CBox                    box; // logical
-        bool                    entered   = false;
-        bool                    hwApplied = false;
+        bool                    entered        = false;
+        bool                    hwApplied      = false;
+        bool                    cursorRendered = false;
 
         SP<Aquamarine::IBuffer> cursorFrontBuffer;
     };
@@ -177,6 +178,7 @@ class CPointerManager {
 
     struct {
         SP<HOOK_CALLBACK_FN> monitorAdded;
+        SP<HOOK_CALLBACK_FN> monitorPreRender;
     } hooks;
 };