!7

cm WebCamDemo > DynPrintLog {
  !include #1029545 // API for Eleu
  
  O html(IWebRequest request) {
    //ret "URI: " + request.uri();
    ret hsansserif() + hfullcenter(p("WebCam Preview")
      + hfulltag video("", autoplay := true, id := "webcamPreview",
          style := "width: 600px; height: 400px; border: 5px solid red;")
      + tag table(tr(
      td(p("Snapshot 1 " + hbutton("Grab", onclick := "snapshot(document.getElementById('snapshotCanvas1'))"))
      + hfulltag canvas("", id := "snapshotCanvas1", width := 300, height := 200, style := "border: 3px solid green;"))
      + td(p("Snapshot 2 " + hbutton("Grab", onclick := "snapshot(document.getElementById('snapshotCanvas2'))"))
      + hfulltag canvas("", id := "snapshotCanvas2", width := 300, height := 200, style := "border: 3px solid green;"))
      + td(p("Diff snapshots " + hbutton("Perform", onclick := "analysis()"))
      + hfulltag canvas("", id := "analysisCanvas", width := 300, height := 200, style := "border: 3px solid green;"))))
    ) + hscript([[
        var video = document.querySelector("#webcamPreview");

        if (navigator.mediaDevices.getUserMedia) {
          navigator.mediaDevices.getUserMedia({ video: true })
            .then(function (stream) {
              video.srcObject = stream;
              getVideoSize();
            })
            .catch(function (err0r) {
              console.log("Something went wrong: " + err0r);
            });
        };

        async function getVideoSize() {
          await new Promise(resolve => video.onloadedmetadata = resolve);
          console.log(`video size: ${video.videoWidth}x${video.videoHeight}`);
        }

        var snapshotW, snapshotH;

        function snapshot(canvas) {
          var w = video.videoWidth, h = video.videoHeight;
          var w2 = canvas.width, h2 = canvas.height;
          if (w/h > w2/h2)
            h2 = Math.round(h*w2/w);
          else
            w2 = Math.round(w*h2/h);
          snapshotW = w2; snapshotH = h2;
          canvas.getContext("2d").drawImage(video, 0, 0, w2, h2);
          canvas.grabbed = true;

          avgBrightness(canvas);
        }

        function avgBrightness(canvas) {
          var imageData = canvas.getContext("2d").getImageData(0, 0, snapshotW, snapshotH);
          var pixels = imageData.data;

          var sum = 0;
          for (var i = 0, il = pixels.length; i < il; i += 4) {
            sum += pixels[i]+pixels[i+1]+pixels[i+2];
          }
          console.log("Brightness: " + sum/(snapshotW*snapshotH*255*3)*100);
        }

        function analysis() {
          if (!document.getElementById('snapshotCanvas1').grabbed)
            snapshot(document.getElementById('snapshotCanvas1'));
            
          snapshot(document.getElementById('snapshotCanvas2'));
          
          var canvas1 = document.getElementById("snapshotCanvas1");
          var canvasCtx1 = canvas1.getContext("2d");
          var canvas2 = document.getElementById("snapshotCanvas2");
          var canvasCtx2 = canvas2.getContext("2d");
          var canvasOut = document.getElementById("analysisCanvas");
          var canvasCtxOut = canvasOut.getContext("2d");
          
          var size = snapshotW*snapshotH;
          var pixels = new Uint8ClampedArray(size*4);
          
          var pixels1 = canvasCtx1.getImageData(0, 0, snapshotW, snapshotH).data;
          var pixels2 = canvasCtx2.getImageData(0, 0, snapshotW, snapshotH).data;
          
          for (var i = 0; i < size*4; i++) {
            if ((i & 3) == 3)
              pixels[i] = 255; // alpha
            else
              pixels[i] = 128+(pixels2[i]-pixels1[i])*0.5;
          }
          
          var palette = canvasCtxOut.getImageData(0, 0, snapshotW, snapshotH);
          palette.data.set(pixels);
          canvasCtxOut.putImageData(palette, 0, 0);
        }
     ]]);
  }
}