[fix] prevent green tint during NV12 scaling

src/common/nv12_scaler.cpp

@@ -0,0 +1,62 @@
+#include "nv12_scaler.h"
+
+#include <cstddef>
+#include <limits>
+
+#include "libyuv/planar_functions.h"
+
+namespace crossdesk {
+
+int ScaleNv12ViaI420(const uint8_t* src_y, int src_stride_y,
+                     const uint8_t* src_uv, int src_stride_uv, int src_width,
+                     int src_height, uint8_t* dst_y, int dst_stride_y,
+                     uint8_t* dst_uv, int dst_stride_uv, int dst_width,
+                     int dst_height, libyuv::FilterMode filtering,
+                     std::vector<uint8_t>* scratch_buffer) {
+  if (!src_y || !src_uv || !dst_y || !dst_uv || !scratch_buffer ||
+      src_width <= 0 || src_height <= 0 || dst_width <= 0 || dst_height <= 0 ||
+      (src_width & 1) != 0 || (src_height & 1) != 0 || (dst_width & 1) != 0 ||
+      (dst_height & 1) != 0) {
+    return -1;
+  }
+
+  const int src_chroma_width = src_width / 2;
+  const int src_chroma_height = src_height / 2;
+  const int dst_chroma_width = dst_width / 2;
+  const int dst_chroma_height = dst_height / 2;
+  const size_t src_chroma_size =
+      static_cast<size_t>(src_chroma_width) * src_chroma_height;
+  const size_t dst_chroma_size =
+      static_cast<size_t>(dst_chroma_width) * dst_chroma_height;
+  const size_t max_size = std::numeric_limits<size_t>::max();
+  if (src_chroma_size > max_size / 2 || dst_chroma_size > max_size / 2) {
+    return -1;
+  }
+
+  const size_t src_planes_size = 2 * src_chroma_size;
+  const size_t dst_planes_size = 2 * dst_chroma_size;
+  if (src_planes_size > max_size - dst_planes_size) {
+    return -1;
+  }
+  scratch_buffer->resize(src_planes_size + dst_planes_size);
+  uint8_t* src_u = scratch_buffer->data();
+  uint8_t* src_v = src_u + src_chroma_size;
+  uint8_t* dst_u = src_v + src_chroma_size;
+  uint8_t* dst_v = dst_u + dst_chroma_size;
+
+  libyuv::SplitUVPlane(src_uv, src_stride_uv, src_u, src_chroma_width, src_v,
+                       src_chroma_width, src_chroma_width, src_chroma_height);
+  const int result = libyuv::I420Scale(
+      src_y, src_stride_y, src_u, src_chroma_width, src_v, src_chroma_width,
+      src_width, src_height, dst_y, dst_stride_y, dst_u, dst_chroma_width,
+      dst_v, dst_chroma_width, dst_width, dst_height, filtering);
+  if (result != 0) {
+    return result;
+  }
+
+  libyuv::MergeUVPlane(dst_u, dst_chroma_width, dst_v, dst_chroma_width, dst_uv,
+                       dst_stride_uv, dst_chroma_width, dst_chroma_height);
+  return 0;
+}
+
+}  // namespace crossdesk

src/common/nv12_scaler.h

@@ -0,0 +1,23 @@
+#ifndef CROSSDESK_COMMON_NV12_SCALER_H_
+#define CROSSDESK_COMMON_NV12_SCALER_H_
+
+#include <cstdint>
+#include <vector>
+
+#include "libyuv/scale.h"
+
+namespace crossdesk {
+
+// Scales NV12 by separating the interleaved chroma plane before filtering.
+// This avoids the downward chroma rounding bias in libyuv::NV12Scale while
+// preserving the requested filtering quality.
+int ScaleNv12ViaI420(const uint8_t* src_y, int src_stride_y,
+                     const uint8_t* src_uv, int src_stride_uv, int src_width,
+                     int src_height, uint8_t* dst_y, int dst_stride_y,
+                     uint8_t* dst_uv, int dst_stride_uv, int dst_width,
+                     int dst_height, libyuv::FilterMode filtering,
+                     std::vector<uint8_t>* scratch_buffer);
+
+}  // namespace crossdesk
+
+#endif  // CROSSDESK_COMMON_NV12_SCALER_H_

src/gui/application/gui_application.cpp

@@ -29,6 +29,7 @@
 #include "crossdesk_ui.h"
 #include "fa_solid_900.h"
 #include "localization.h"
+#include "nv12_scaler.h"
 #include "platform.h"
 #if _WIN32
 #include <windows.h>
@@ -866,6 +867,7 @@ struct GuiApplication::SlintUi {
           std::make_shared<slint::VectorModel<slint::SharedString>>();
   std::unordered_map<std::string, uint64_t> displayed_frame_sequence;
   std::vector<uint8_t> scaled_video_frame;
+  std::vector<uint8_t> scaled_video_frame_scratch;
 #if !defined(__APPLE__)
   std::mutex video_gl_mutex;
   std::vector<uint8_t> video_gl_conversion_frame;
@@ -2651,10 +2653,11 @@ void GuiApplication::SyncStreamVideoFrame() {
     uint8_t* scaled_uv =
         scaled_y +
         static_cast<size_t>(render_size.width) * render_size.height;
-    if (libyuv::NV12Scale(y_plane, width, uv_plane, width, width, height,
-                         scaled_y, render_size.width, scaled_uv,
-                         render_size.width, render_size.width,
-                         render_size.height, libyuv::kFilterBox) == 0) {
+    if (ScaleNv12ViaI420(
+            y_plane, width, uv_plane, width, width, height, scaled_y,
+            render_size.width, scaled_uv, render_size.width, render_size.width,
+            render_size.height, libyuv::kFilterBox,
+            &ui_->scaled_video_frame_scratch) == 0) {
       y_plane = scaled_y;
       uv_plane = scaled_uv;
       output_width = render_size.width;

xmake/targets.lua

@@ -33,6 +33,7 @@ function setup_targets()
     target("common")
         set_kind("object")
         add_deps("rd_log")
+        add_packages("libyuv")
         add_files("src/common/*.cpp")
         remove_files("src/common/rounded_corner_button.cpp")
         if is_os("macosx") then