dmonitoringmodeld: fix black padding not black after libyuv.I420Scale (#22971)

* true black

* set black once

* move def

* add commnet

* Update selfdrive/modeld/models/dmonitoring.cc

* Update selfdrive/modeld/models/dmonitoring.cc

* Update selfdrive/modeld/models/dmonitoring.cc

* Update selfdrive/modeld/models/dmonitoring.cc

Co-authored-by: Adeeb Shihadeh <adeebshihadeh@gmail.com>

selfdrive/modeld/models/dmonitoring.cc

@@ -13,11 +13,30 @@
 #define MODEL_HEIGHT 640
 #define FULL_W 852 // should get these numbers from camerad
 
+template <class T>
+static inline T *get_buffer(std::vector<T> &buf, const size_t size) {
+  if (buf.size() < size) buf.resize(size);
+  return buf.data();
+}
+
+static inline void init_yuv_buf(std::vector<uint8_t> &buf, const int width, int height) {
+  uint8_t *y = get_buffer(buf, width * height * 3 / 2);
+  uint8_t *u = y + width * height;
+  uint8_t *v = u + (width / 2) * (height / 2);
+
+  // needed on comma two to make the padded border black
+  // equivalent to RGB(0,0,0) in YUV space
+  memset(y, 16, width * height);
+  memset(u, 128, (width / 2) * (height / 2));
+  memset(v, 128, (width / 2) * (height / 2));
+}
+
 void dmonitoring_init(DMonitoringModelState* s) {
   s->is_rhd = Params().getBool("IsRHD");
   for (int x = 0; x < std::size(s->tensor); ++x) {
     s->tensor[x] = (x - 128.f) * 0.0078125f;
   }
+  init_yuv_buf(s->resized_buf, MODEL_WIDTH, MODEL_HEIGHT);
 
 #ifdef USE_ONNX_MODEL
   s->m = new ONNXModel("../../models/dmonitoring_model.onnx", &s->output[0], OUTPUT_SIZE, USE_DSP_RUNTIME);
@@ -26,12 +45,6 @@ void dmonitoring_init(DMonitoringModelState* s) {
 #endif
 }
 
-template <class T>
-static inline T *get_buffer(std::vector<T> &buf, const size_t size) {
-  if (buf.size() < size) buf.resize(size);
-  return buf.data();
-}
-
 static inline auto get_yuv_buf(std::vector<uint8_t> &buf, const int width, int height) {
   uint8_t *y = get_buffer(buf, width * height * 3 / 2);
   uint8_t *u = y + width * height;