這次帶給大家如何使用canvas來製作好用的塗鴉畫板，使用canvas來製作好用的塗鴉畫板的注意事項有哪些，下面就是實戰案例，一起來看一下。在canvas中取得遊標座標
取得座標的程式碼很簡單:
<!DOCTYPE html><html lang="en"><head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
*{margin: 0;padding: 0} </style></head><body>
<canvas id="board" style="border: 1px #ccc solid;"></canvas>
<span id="point"></span>
<script>
var canvas = document.getElementById('board'); var context = canvas.getContext('2d'); var current = { color: 'black',//<===画笔颜色配置
width: 1//线条宽度
}; //获取点坐标
function getPoint(e) { if (e.touches && e.touches.length > 0) { var touch = e.touches[0]; return { x: touch.pageX, y: touch.pageY };
} return { x: e.clientX, y: e.clientY };
} //鼠标移动
function onMouseMove(e) { var p = getPoint(e); document.getElementById("point").innerHTML=p.x+"-"+p.y;
}
canvas.width = 600;
canvas.height = 300;
canvas.addEventListener('mousemove', onMouseMove, false); //<==兼容PC
canvas.addEventListener('touchmove', onMouseMove, false);//<===兼容安卓或其他系统
</script></body></html>登入後複製
注意:因為滑鼠與觸控螢幕的事件是不一樣的,滑鼠只要懸浮與canvas上就可以取得到了,而觸控螢幕是需要按下的,並且所回傳的Event 物件也是不一樣的。
2.控制是否繪製
控制是否繪製其實很簡單,就是在不同事件時判斷自定義變數drawing的值來控制
<!DOCTYPE html><html lang="en"><head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<style>
*{margin: 0;padding: 0} </style></head><body>
<canvas id="board" style="border: 1px #ccc solid;"></canvas>
<span id="point"></span>
<script>
var canvas = document.getElementById('board'); var context = canvas.getContext('2d'); var current = { color: 'black',//<===画笔颜色配置
width: 1//线条宽度
}; var drawing = false;//<===是否绘制
//获取点坐标
function getPoint(e) { if (e.touches && e.touches.length > 0) { var touch = e.touches[0]; return { x: touch.pageX, y: touch.pageY };
} return { x: e.clientX, y: e.clientY };
} //鼠标按下
function onMouseDown(e) {
drawing = true;
} //鼠标弹起
function onMouseUp(e) { if (!drawing) { return; }
drawing = false;
} //鼠标移动
function onMouseMove(e) { if (!drawing) { return; } var p = getPoint(e); document.getElementById("point").innerHTML=p.x+"-"+p.y;
}
canvas.width = 600;
canvas.height = 300;
canvas.addEventListener('mousedown', onMouseDown, false);
canvas.addEventListener('mouseup', onMouseUp, false);
canvas.addEventListener('mouseout', onMouseUp, false);
canvas.addEventListener('mousemove', onMouseMove, false);
canvas.addEventListener('touchstart', onMouseDown, false);
canvas.addEventListener('touchend', onMouseUp, false);
canvas.addEventListener('touchmove', onMouseMove, false); </script></body></html>登入後複製
3.線條繪製
線條繪製的程式碼也是很簡單的
....//线条绘制function drawLine(x0, y0, x1, y1, color, width) {
context.beginPath();
context.moveTo(x0, y0);
context.lineTo(x1, y1);
context.strokeStyle = color;
context.lineWidth = width;
context.stroke();
context.closePath();
}
....登入後複製
將繪製線條程式碼整合到事件中:
<!DOCTYPE html><html lang="en"><head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title></head><body>
<canvas id="board" style="border: 1px #ccc solid;"></canvas>
<span id="point"></span>
<script>
var canvas = document.getElementById('board'); var context = canvas.getContext('2d'); var current = { color: 'black',//<===画笔颜色配置
width: 1//线条宽度
}; var drawing = false;//<===是否绘制
//获取点坐标
function getPoint(e) { if (e.touches && e.touches.length > 0) { var touch = e.touches[0]; return { x: touch.pageX, y: touch.pageY };
} return { x: e.clientX, y: e.clientY };
} //线条绘制
function drawLine(x0, y0, x1, y1, color, width) {
context.beginPath();
context.moveTo(x0, y0);
context.lineTo(x1, y1);
context.strokeStyle = color;
context.lineWidth = width;
context.stroke();
context.closePath();
} //鼠标按下
function onMouseDown(e) {
drawing = true; //记录按下点
var p = getPoint(e);
current.x = p.x;
current.y = p.y;
} //鼠标弹起
function onMouseUp(e) { if (!drawing) { return; }
drawing = false; //绘制结束点
var p = getPoint(e);
drawLine(current.x, current.y, p.x, p.y, current.color, current.width);
} //鼠标移动
function onMouseMove(e) { if (!drawing) { return; } var p = getPoint(e); document.getElementById("point").innerHTML = p.x + "-" + p.y; //移动绘制
drawLine(current.x, current.y, p.x, p.y, current.color, current.width);
current.x = p.x;
current.y = p.y;
}
canvas.width = 600;
canvas.height = 300;
canvas.addEventListener('mousedown', onMouseDown, false);
canvas.addEventListener('mouseup', onMouseUp, false);
canvas.addEventListener('mouseout', onMouseUp, false);
canvas.addEventListener('mousemove', onMouseMove, false);
canvas.addEventListener('touchstart', onMouseDown, false);
canvas.addEventListener('touchend', onMouseUp, false);
canvas.addEventListener('touchmove', onMouseMove, false); </script></body></html>登入後複製
4.繪製線條最佳化
當繪製線條寬度比較小的時候還好,一旦比較粗就會有寫問題:
這時只要稍微改一下繪製的程式碼就行了
....//线条绘制function drawLine(x0, y0, x1, y1, color, width) {
context.beginPath();
context.moveTo(x0, y0);
context.lineTo(x1, y1);
context.strokeStyle = color;
context.lineWidth = width;
//-----加入-----
context.lineCap = "round";
context.lineJoin = "round"; //-----加入-----
context.stroke();
context.closePath();
}
....登入後複製
相信看了本文案例你已經掌握了方法，更多精彩請關注php中文網其它相關文章！
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以上是如何使用canvas來製作好用的塗鴉畫板的詳細內容。更多資訊請關注PHP中文網其他相關文章！
