Display an image using the video pipeline

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Original author	Amir Hassan (kallaballa) amir@.nosp@m.viel.nosp@m.-zu.o.nosp@m.rg
Compatibility	OpenCV >= 4.7

Using the video pipeline

Actually there are several ways to display an image using V4D. The most convenient way is to use the video pipeline to feed an image to V4D. That has the advantage that the image is automatically resized (preserving aspect ratio) to framebuffer size and color converted (the framebuffer is BGRA while video frames are expected to be BGR).

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#include <opencv2/v4d/v4d.hpp>
#include <opencv2/imgcodecs.hpp>
 
using namespace cv;
using namespace cv::v4d;
 
class DisplayImagePlan : public Plan {
    UMat image_;
public:
    void setup(Ptr<V4D> win) override {
        win->parallel([](cv::UMat& image){
#ifdef __EMSCRIPTEN__
        image = read_embedded_image("doc/lena.png").getUMat(ACCESS_READ);
#else
        image = imread(samples::findFile("lena.jpg")).getUMat(ACCESS_READ);
#endif
        }, image_);
    }
 
    void infer(Ptr<V4D> win) override {
        //Feeds the image to the video pipeline
        win->feed(image_);
    }
};
 
int main() {
    //Creates a V4D window for on screen rendering with a window size of 960x960 and a framebuffer of the same size.
    //Please note that while the window size may change the framebuffer size may not. If you need multiple framebuffer
    //sizes you need multiple V4D objects
    cv::Ptr<V4D> window = V4D::make(960, 960, "Display an Image");
    window->run<DisplayImagePlan>(0);
}