Performance improvements, better readme and complete python bindings

examples/09_opencv_cellshade/main.cpp

@@ -8,6 +8,12 @@
 #include <thread>
 #include <chrono>
 
+// Teach KPN how many bytes a cv::Mat actually carries (header + pixel data).
+template<>
+struct kpn::ChannelDataSize<cv::Mat> {
+    static std::size_t bytes(const cv::Mat& m) { return m.total() * m.elemSize(); }
+};
+
 // ── Cell-shading pipeline ─────────────────────────────────────────────────────
 //
 //  [capture] --"colour"--> [quantise] ──────────────────────────┐
@@ -32,6 +38,7 @@ static cv::Mat make_gradient(int W, int H) {
 
 // ── Pipeline functions ────────────────────────────────────────────────────────
 
+// [snippet: capture_fn]
 static std::tuple<cv::Mat, cv::Mat> capture() {
     constexpr int W = 640, H = 480;
     static cv::VideoCapture cap;
@@ -68,6 +75,7 @@ static std::tuple<cv::Mat, cv::Mat> capture() {
     }
     return {frame.clone(), frame.clone()};
 }
+// [/snippet: capture_fn]
 
 static cv::Mat to_gray(cv::Mat bgr) {
     cv::Mat gray;
@@ -112,6 +120,7 @@ static std::tuple<cv::Mat, cv::Mat> composite(cv::Mat edge_mask, cv::Mat colour)
 // The constructor opens both windows on the main thread (Wayland requirement).
 // operator() is called by step() whenever both channels have a frame ready.
 
+// [snippet: display_node]
 class DisplayNode : public kpn::MainThreadNode<DisplayNode,
                                                kpn::in<"composite", "edges">,
                                                cv::Mat, cv::Mat> {
@@ -141,12 +150,14 @@ private:
         catch (const cv::Exception&) { return false; }
     }
 };
+// [/snippet: display_node]
 
 // ─────────────────────────────────────────────────────────────────────────────
 
 int main() {
     using namespace kpn;
 
+    // [snippet: opencv_network]
     auto src       = make_node<capture>  (out<"colour","grey">{},            8);
     auto gray_node = make_node<to_gray>  (in<"bgr">{},   out<"gray">{},      8);
     auto edge_node = make_node<edges_fn> (in<"gray">{},  out<"edges">{},     8);
@@ -171,13 +182,17 @@ int main() {
        .connect("comp",  comp.template output<"result">(),     "display", disp.template input<"composite">())
        .connect("comp",  comp.template output<"edges">(),      "display", disp.template input<"edges">())
        .build();
+    // [/snippet: opencv_network]
 
     net.set_watchdog_interval(std::chrono::milliseconds(5000));
+#ifdef KPN_WEB_DEBUG
     net.set_web_debug_port(9090);
+#endif
 
     std::cout << "Cell-shading pipeline running. Press 'q' to stop.\n";
     std::cout << "Web debug UI: http://localhost:9090\n";
 
+    // [snippet: main_thread_step]
     net.start();
 
     // Main thread drives display — imshow/waitKey stay on the GUI thread.
@@ -186,5 +201,6 @@ int main() {
         cv::waitKey(8); // yield event loop when no frame ready
 
     net.stop();
+    // [/snippet: main_thread_step]
     return 0;
 }