From 859c78fdc0f09045ffedf2345db486efe3bbecc5 Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Mon, 21 Jun 2021 22:04:59 +1000
Subject: [PATCH] DRMDisplay: Restore previous framebuffer on shutdown

---
 src/common/drm_display.cpp        | 17 +++++++++++++++++
 src/common/drm_display.h          |  5 +++++
 src/common/gl/context_egl_gbm.cpp |  2 ++
 3 files changed, 24 insertions(+)

diff --git a/src/common/drm_display.cpp b/src/common/drm_display.cpp
index a667475ed..ef64d3d47 100644
--- a/src/common/drm_display.cpp
+++ b/src/common/drm_display.cpp
@@ -19,6 +19,10 @@ DRMDisplay::DRMDisplay(int card /*= 1*/) : m_card_id(card) {}
 
 DRMDisplay::~DRMDisplay()
 {
+  // restore original buffer
+  if (m_prev_crtc)
+    RestoreBuffer();
+
   if (m_connector)
     drmModeFreeConnector(m_connector);
 
@@ -90,6 +94,18 @@ bool DRMDisplay::Initialize(u32 width, u32 height, float refresh_rate)
   return TryOpeningCard(m_card_id, width, height, refresh_rate);
 }
 
+void DRMDisplay::RestoreBuffer()
+{
+  if (m_prev_crtc)
+  {
+    u32 connector_id = m_connector->connector_id;
+    drmModeSetCrtc(m_card_fd, m_prev_crtc->crtc_id, m_prev_crtc->buffer_id, m_prev_crtc->x, m_prev_crtc->y,
+                   &connector_id, 1, &m_prev_crtc->mode);
+    drmModeFreeCrtc(m_prev_crtc);
+    m_prev_crtc = nullptr;
+  }
+}
+
 bool DRMDisplay::TryOpeningCard(int card, u32 width, u32 height, float refresh_rate)
 {
   if (m_card_fd >= 0)
@@ -201,6 +217,7 @@ bool DRMDisplay::TryOpeningCard(int card, u32 width, u32 height, float refresh_r
   drmModeFreeResources(resources);
 
   m_card_id = card;
+  m_prev_crtc = drmModeGetCrtc(m_card_fd, m_crtc_id);
   return true;
 }
 
diff --git a/src/common/drm_display.h b/src/common/drm_display.h
index 1ef019c33..4125681ce 100644
--- a/src/common/drm_display.h
+++ b/src/common/drm_display.h
@@ -15,6 +15,9 @@ public:
 
   bool Initialize(u32 width, u32 height, float refresh_rate);
 
+  /// Restores the buffer saved at startup.
+  void RestoreBuffer();
+
   int GetCardID() const { return m_card_id; }
   int GetCardFD() const { return m_card_fd; }
   u32 GetWidth() const { return m_mode->hdisplay; }
@@ -53,4 +56,6 @@ private:
   drmModeRes* m_resources = nullptr;
   drmModeConnector* m_connector = nullptr;
   drmModeModeInfo* m_mode = nullptr;
+
+  drmModeCrtc* m_prev_crtc = nullptr;
 };
diff --git a/src/common/gl/context_egl_gbm.cpp b/src/common/gl/context_egl_gbm.cpp
index 8a8163af2..2c67581c9 100644
--- a/src/common/gl/context_egl_gbm.cpp
+++ b/src/common/gl/context_egl_gbm.cpp
@@ -21,6 +21,8 @@ ContextEGLGBM::~ContextEGLGBM()
   Assert(!m_current_present_buffer);
 #endif
 
+  m_drm_display.RestoreBuffer();
+
   // We have to destroy the context before the surface/device.
   // Leaving it to the base class would be too late.
   DestroySurface();