[refactor] modularize Slint video rendering backends

src/gui/platform/video_renderer.h

@@ -0,0 +1,70 @@
+#ifndef CROSSDESK_GUI_PLATFORM_VIDEO_RENDERER_H_
+#define CROSSDESK_GUI_PLATFORM_VIDEO_RENDERER_H_
+
+#include <cstddef>
+#include <cstdint>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace crossdesk {
+
+// Platform-independent contract for the native stream video renderer.
+//
+// Frame submission and snapshot methods may be called from MiniRTC callback
+// threads. Surface setup, rendering and teardown remain backend-specific and
+// are driven by the Slint presentation module on the UI thread.
+class VideoRenderer {
+public:
+  enum class SubmitResult {
+    submitted,
+    not_selected,
+    dropped,
+    failed,
+  };
+
+  enum class RenderResult {
+    rendered,
+    idle,
+    empty,
+    failed,
+  };
+
+  struct RenderOutcome {
+    RenderResult result = RenderResult::failed;
+    int width = 0;
+    int height = 0;
+    uint64_t sequence = 0;
+  };
+
+  virtual ~VideoRenderer() = default;
+
+  virtual bool IsReady() const = 0;
+
+  // True only while the renderer can accept and present native frames. Metal
+  // additionally requires attachment to an AppKit view; OpenGL requires an
+  // active Slint rendering context.
+  virtual bool IsActive() const = 0;
+
+  virtual bool SetSelectedStream(std::string remote_id) = 0;
+  virtual void DiscardStream(std::string_view remote_id) = 0;
+
+  virtual SubmitResult SubmitNv12(std::string_view remote_id,
+                                  const uint8_t* data, size_t size, int width,
+                                  int height) = 0;
+  virtual SubmitResult SubmitCachedNv12(std::string_view remote_id,
+                                        const uint8_t* data, size_t size,
+                                        int width, int height) = 0;
+
+  virtual bool CopyLatestNv12(std::string_view remote_id,
+                              std::vector<unsigned char>* output, int* width,
+                              int* height) const = 0;
+};
+
+// Exactly one factory implementation is linked for the target platform.
+std::unique_ptr<VideoRenderer> CreateVideoRenderer();
+
+}  // namespace crossdesk
+
+#endif  // CROSSDESK_GUI_PLATFORM_VIDEO_RENDERER_H_