如何使用javascript捕获网络摄像头上的特定坐标？

Question

i know how to capture video , this is my code

var context = canvas.getContext('2d');
snap.addEventListener("click", function() {
    context.drawImage(video, 0, 0, 1000, 500);

});

but how to capture specific coordinates ?

change drawImage() function parametere just resize the picture but still capture whole picture

Answer 1

You can't avoid capturing the entire camera frame, because that's just how the camera API works. But you can use the overload of drawImage that takes a source rectangle as an argument:

context.drawImage(video, sx, sy, sWidth, sHeight, 0, 0, 1000, 500);

Here, sx, sy, sWidth, sHeight indicates the rectangle inside the video frame that you want to draw. This is then stretched to fit inside the destination rectangle; if you don't want any stretching, make sure the width and height are the same.