[fix] resolve failures in the WGC→DXGI→GDI fallback chain

src/screen_capturer/windows/screen_capturer_win.cpp

@@ -1,6 +1,9 @@
 #include "screen_capturer_win.h"
 
+#include <cmath>
 #include <memory>
+#include <string>
+#include <vector>
 
 #include "rd_log.h"
 #include "screen_capturer_dxgi.h"
@@ -14,7 +17,26 @@ ScreenCapturerWin::~ScreenCapturerWin() { Destroy(); }
 
 int ScreenCapturerWin::Init(const int fps, cb_desktop_data cb) {
   fps_ = fps;
-  cb_ = cb;
+  cb_orig_ = cb;
+  cb_ = [this](unsigned char* data, int size, int w, int h,
+               const char* display_name) {
+    std::string mapped_name;
+    {
+      std::lock_guard<std::mutex> lock(alias_mutex_);
+      auto it = label_alias_.find(display_name);
+      if (it != label_alias_.end())
+        mapped_name = it->second;
+      else
+        mapped_name = display_name;
+    }
+    {
+      std::lock_guard<std::mutex> lock(alias_mutex_);
+      if (canonical_labels_.find(mapped_name) == canonical_labels_.end()) {
+        return;
+      }
+    }
+    if (cb_orig_) cb_orig_(data, size, w, h, mapped_name.c_str());
+  };
 
   int ret = -1;
 
@@ -22,6 +44,7 @@ int ScreenCapturerWin::Init(const int fps, cb_desktop_data cb) {
   ret = impl_->Init(fps_, cb_);
   if (ret == 0) {
     LOG_INFO("Windows capturer: using WGC");
+    BuildCanonicalFromImpl();
     return 0;
   }
 
@@ -32,6 +55,7 @@ int ScreenCapturerWin::Init(const int fps, cb_desktop_data cb) {
   ret = impl_->Init(fps_, cb_);
   if (ret == 0) {
     LOG_INFO("Windows capturer: using DXGI Desktop Duplication");
+    BuildCanonicalFromImpl();
     return 0;
   }
 
@@ -42,6 +66,7 @@ int ScreenCapturerWin::Init(const int fps, cb_desktop_data cb) {
   ret = impl_->Init(fps_, cb_);
   if (ret == 0) {
     LOG_INFO("Windows capturer: using GDI BitBlt");
+    BuildCanonicalFromImpl();
     return 0;
   }
 
@@ -55,12 +80,52 @@ int ScreenCapturerWin::Destroy() {
     impl_->Destroy();
     impl_.reset();
   }
+  {
+    std::lock_guard<std::mutex> lock(alias_mutex_);
+    label_alias_.clear();
+    handle_to_canonical_.clear();
+    canonical_labels_.clear();
+  }
   return 0;
 }
 
 int ScreenCapturerWin::Start(bool show_cursor) {
   if (!impl_) return -1;
-  return impl_->Start(show_cursor);
+  int ret = impl_->Start(show_cursor);
+  if (ret == 0) return 0;
+
+  LOG_WARN("Windows capturer: Start failed (ret={}), trying fallback", ret);
+
+  auto try_init_start = [&](std::unique_ptr<ScreenCapturer> cand) -> bool {
+    int r = cand->Init(fps_, cb_);
+    if (r != 0) return false;
+    int s = cand->Start(show_cursor);
+    if (s == 0) {
+      impl_ = std::move(cand);
+      RebuildAliasesFromImpl();
+      return true;
+    }
+    return false;
+  };
+
+  if (dynamic_cast<ScreenCapturerWgc*>(impl_.get())) {
+    if (try_init_start(std::make_unique<ScreenCapturerDxgi>())) {
+      LOG_INFO("Windows capturer: fallback to DXGI");
+      return 0;
+    }
+    if (try_init_start(std::make_unique<ScreenCapturerGdi>())) {
+      LOG_INFO("Windows capturer: fallback to GDI");
+      return 0;
+    }
+  } else if (dynamic_cast<ScreenCapturerDxgi*>(impl_.get())) {
+    if (try_init_start(std::make_unique<ScreenCapturerGdi>())) {
+      LOG_INFO("Windows capturer: fallback to GDI");
+      return 0;
+    }
+  }
+
+  LOG_ERROR("Windows capturer: all fallbacks failed to start");
+  return ret;
 }
 
 int ScreenCapturerWin::Stop() {
@@ -88,4 +153,46 @@ std::vector<DisplayInfo> ScreenCapturerWin::GetDisplayInfoList() {
   return impl_->GetDisplayInfoList();
 }
 
-}  // namespace crossdesk
+void ScreenCapturerWin::BuildCanonicalFromImpl() {
+  std::lock_guard<std::mutex> lock(alias_mutex_);
+  handle_to_canonical_.clear();
+  label_alias_.clear();
+  canonical_displays_ = impl_->GetDisplayInfoList();
+  canonical_labels_.clear();
+  for (const auto& di : canonical_displays_) {
+    handle_to_canonical_[di.handle] = di.name;
+    canonical_labels_.insert(di.name);
+  }
+}
+
+void ScreenCapturerWin::RebuildAliasesFromImpl() {
+  std::lock_guard<std::mutex> lock(alias_mutex_);
+  label_alias_.clear();
+  auto current = impl_->GetDisplayInfoList();
+  auto similar = [&](const DisplayInfo& a, const DisplayInfo& b) {
+    int dl = std::abs(a.left - b.left);
+    int dt = std::abs(a.top - b.top);
+    int dw = std::abs(a.width - b.width);
+    int dh = std::abs(a.height - b.height);
+    return dl <= 10 && dt <= 10 && dw <= 20 && dh <= 20;
+  };
+  for (const auto& di : current) {
+    std::string canonical;
+    auto it = handle_to_canonical_.find(di.handle);
+    if (it != handle_to_canonical_.end()) {
+      canonical = it->second;
+    } else {
+      for (const auto& c : canonical_displays_) {
+        if (similar(di, c) || (di.is_primary && c.is_primary)) {
+          canonical = c.name;
+          break;
+        }
+      }
+    }
+    if (!canonical.empty() && canonical != di.name) {
+      label_alias_[di.name] = canonical;
+    }
+  }
+}
+
+}  // namespace crossdesk