javascript - The picture I draw is invisible after I reset the width and height of the canvas -

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in js file:

function main_part2() {     var canvas = document.getelementbyid("viewport");     var context = canvas.getcontext("2d");     var eye = new vector(0.5, 0.5, -0.5);      raycasting(context, eye, part2); } function change_size() {     var canvas = document.getelementbyid("viewport");     var width = document.getelementbyid("width").value;     var height = document.getelementbyid("height").value;     canvas.width = width;     canvas.height = height;     main_part2(); }

in html file:

<body onload="main_part2();"> <canvas id="viewport" width="512" height="512" style="background-color: black"></canvas><br><br> <label for="width">width: </label><input id="width" type="number"><br><br> <label for="height">height: </label><input id="height" type="number"><br><br> <button type="submit" onclick="change_size()">change</button>

i try reset width , height of canvas through 2 inputs , draw new picture according new canvas. however, when click button, canvas resized, raycasting function, draw picture, makes no effect. how make work?


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