HTML5畫布drawImage圖像大小不正確

Question

您好我有問題我嘗試在畫布上使用drawImage函數50px x 50px在50px x 50px畫布上繪制圖像，但我比我需要的要小。

 var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var img = new Image(); img.onload = function() { $("canvas").css("width", 50); $("canvas").css("height", 50); ctx.drawImage(img, 0, 0, 50, 50); //bad here why not drawing 50x50px image on the canvas? } img.src = 'http://www.w3schools.com/tags/planets.gif'; 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script> <img src="http://www.w3schools.com/tags/planets.gif" width="100" height="100" style="position: absolute; top: 0px; left: 0px"> <canvas id="canvas" style="position: absolute; top: 0px; left: 120px; border: 1px solid #000"></canvas> 

Answer 1

不要通過CSS設置畫布的寬度和高度。 這將拉伸/壓縮實際畫布，縮放內容。

請改用舊的HTML width和height屬性：

 var canvas = document.getElementById("canvas"); var ctx = canvas.getContext("2d"); var img = new Image(); img.onload = function() { ctx.drawImage(img, 0, 0, 50, 50); } img.src = 'http://www.w3schools.com/tags/planets.gif'; 

 <img src="http://www.w3schools.com/tags/planets.gif" width="100" height="100" style="position: absolute; top: 0px; left: 0px"> <canvas id="canvas" style="position: absolute; top: 0px; left: 120px; border: 1px solid #000" width="50" height="50"> </canvas> 

這些屬性實際上會更改畫布的上下文的寬度和高度，從而產生與您期望的大小完全相同的圖像。