From 0327a137e069e0cfbdd775f7c40f03e088b765d6 Mon Sep 17 00:00:00 2001
From: "zejian.su" <zejian.su@starfivetech.com>
Date: Wed, 8 Nov 2023 09:23:01 +0800
Subject: [PATCH 2/2] Make the qt preview work in debian. 1. Fill the NV12 data
 into the QT buffer. 2. For the low performance of QWidget, reduce the FPS to
 15.

Signed-off-by: zejian.su <zejian.su@starfivetech.com>
---
 preview/preview.cpp    | 37 ++++++++++++++-----------------------
 preview/qt_preview.cpp | 20 ++++++++++++++++----
 2 files changed, 30 insertions(+), 27 deletions(-)

diff --git a/preview/preview.cpp b/preview/preview.cpp
index b67edb3..d2c511a 100644
--- a/preview/preview.cpp
+++ b/preview/preview.cpp
@@ -19,47 +19,38 @@ Preview *make_preview(Options const *options)
 	if (options->nopreview)
 		return make_null_preview(options);
 #if QT_PRESENT
-	else if (options->qt_preview)
+	else
 	{
 		Preview *p = make_qt_preview(options);
 		if (p)
 			LOG(1, "Made QT preview window");
 		return p;
 	}
-#endif
-	else
+#else
+	try
+	{
+		throw std::runtime_error("qt5 libraries unavailable.");
+	}
+	catch(std::exception const &e)
 	{
 		try
 		{
-#if LIBEGL_PRESENT
-			Preview *p = make_egl_preview(options);
+#if LIBDRM_PRESENT
+			Preview *p = make_drm_preview(options);
 			if (p)
-				LOG(1, "Made X/EGL preview window");
+				LOG(1, "Made DRM preview window");
 			return p;
 #else
-			throw std::runtime_error("egl libraries unavailable.");
+			throw std::runtime_error("drm libraries unavailable.");
 #endif
 		}
 		catch (std::exception const &e)
 		{
-			try
-			{
-#if LIBDRM_PRESENT
-				Preview *p = make_drm_preview(options);
-				if (p)
-					LOG(1, "Made DRM preview window");
-				return p;
-#else
-				throw std::runtime_error("drm libraries unavailable.");
-#endif
-			}
-			catch (std::exception const &e)
-			{
-				LOG(1, "Preview window unavailable");
-				return make_null_preview(options);
-			}
+			LOG(1, "Preview window unavailable");
+			return make_null_preview(options);
 		}
 	}
+#endif
 
 	return nullptr; // prevents compiler warning in debug builds
 }
diff --git a/preview/qt_preview.cpp b/preview/qt_preview.cpp
index f595db7..8196a8e 100644
--- a/preview/qt_preview.cpp
+++ b/preview/qt_preview.cpp
@@ -58,7 +58,7 @@ protected:
 class QtPreview : public Preview
 {
 public:
-	QtPreview(Options const *options) : Preview(options)
+	QtPreview(Options const *options) : Preview(options), frame_counter_(0)
 	{
 		window_width_ = options->preview_width;
 		window_height_ = options->preview_height;
@@ -83,6 +83,12 @@ public:
 	void SetInfoText(const std::string &text) override { main_window_->setWindowTitle(QString::fromStdString(text)); }
 	virtual void Show(int fd, libcamera::Span<uint8_t> span, StreamInfo const &info) override
 	{
+		if((frame_counter_++) & 1) {
+			// Return the buffer to the camera system.
+			done_callback_(fd);
+			return;
+		}
+		
 		// Quick and simple nearest-neighbour-ish resampling is used here.
 		// We further share U,V samples between adjacent output pixel pairs
 		// (even when downscaling) to speed up the conversion.
@@ -131,6 +137,7 @@ public:
 		// take a copy of each row used. This is a speedup provided memcpy() is vectorized.
 		tmp_stripe_.resize(2 * info.stride);
 		uint8_t const *Y_start = span.data();
+		uint8_t const *UV_start = Y_start + info.height * info.stride;
 		uint8_t *Y_row = &tmp_stripe_[0];
 		uint8_t *U_row = Y_row + info.stride;
 		uint8_t *V_row = U_row + (info.stride >> 1);
@@ -146,8 +153,11 @@ public:
 			unsigned x_pos = x_step >> 1;
 
 			memcpy(Y_row, Y_start + row * info.stride, info.stride);
-			memcpy(U_row, Y_start + ((4 * info.height + row) >> 1) * (info.stride >> 1), info.stride >> 1);
-			memcpy(V_row, Y_start + ((5 * info.height + row) >> 1) * (info.stride >> 1), info.stride >> 1);
+			//memcpy(U_row, Y_start + ((4 * info.height + row) >> 1) * (info.stride >> 1), info.stride >> 1);
+			//memcpy(V_row, Y_start + ((5 * info.height + row) >> 1) * (info.stride >> 1), info.stride >> 1);
+			uint8_t const *cur_uv = UV_start + (row >> 1) * info.width;
+			for(unsigned int uv_idx = 0; uv_idx < info.width >> 1; uv_idx++, cur_uv += 2)
+				U_row[uv_idx] = cur_uv[0], V_row[uv_idx] = cur_uv[1];
 
 			for (unsigned int x = 0; x < window_width_; x += 2)
 			{
@@ -183,7 +193,7 @@ public:
 	}
 	// Reset the preview window, clearing the current buffers and being ready to
 	// show new ones.
-	void Reset() override {}
+	void Reset() override {frame_counter_ = 0;}
 	// Check if preview window has been shut down.
 	bool Quit() override { return main_window_->quit; }
 	// There is no particular limit to image sizes, though large images will be very slow.
@@ -218,6 +228,8 @@ private:
 	std::mutex mutex_;
 	std::condition_variable cond_var_;
 	std::vector<uint8_t> tmp_stripe_;
+
+	unsigned int frame_counter_;
 };
 
 Preview *make_qt_preview(Options const *options)
-- 
2.34.1