我有这样的功能:
function fillSlide(slideId){
var context_background = new Image();
context_background.src = './images/'+slideId+'.png';
context_background.onload = function(){
var canvas = document.getElementById(slideId);
window.addEventListener('resize', resizeCanvas, false);
if(canvas.getContext){
var context = canvas.getContext('2d');
var pattern = context.createPattern(this,'no-repeat');
function resizeCanvas() {
var width = window.innerWidth;
var height = document.getElementsByClassName('slidecont')[0].offsetHeight;
height += 50;
canvas.width = width;
canvas.height = height;
drawStuff(context,width,pattern);
}
resizeCanvas();
function drawStuff(ctx,w,p) {
var l = w/2 - 120;
var r = w/2 + 120;
context.fillStyle = p;
ctx.save();
ctx.beginPath();
ctx.moveTo(0,50);
ctx.lineTo(0,1924.06925);
ctx.lineTo(w,1924.06925);
ctx.lineTo(w,50);
ctx.lineTo(r,50);
ctx.bezierCurveTo((r-35),50,(r-70),0,(r-120),0);
ctx.bezierCurveTo((l+70),0,(l+49),50,l,50);
ctx.lineTo(0,50);
ctx.closePath();
ctx.fill();
ctx.restore();
}
}
};
}
如您所见,我正在使用 Image() 元素创建图案并用它填充上下文。我想用这个图案作为背景。但是 Canvas 中没有背景大小样式。
如我所见,我需要在填充 Canvas 之前剪切图案元素。我该如何管理?谢谢。
更新:JSFIDDLE
最佳答案
也许我的回复不值得添加答案,但我还不能添加评论。
我认为this可能对你有帮助。
编辑
您不需要 fillStyle 模式来用图像填充形状。 另一种方法是:
- 画出路径
- 在上下文对象上调用
clip
方法(这将裁剪每个绘制的对象以匹配路径指定的形状) - 使用
drawImage
方法代替图案,这样您就可以设置合适的尺寸。
看看我的jsfiddle snippet
var canvas = document.getElementById('slide');
var ctx = canvas.getContext('2d');
var img = new Image();
function draw() {
var w = canvas.width;
var h = canvas.height;
var l = w/2 - 120;
var r = w/2 + 120;
ctx.save();
ctx.beginPath();
ctx.moveTo(0,50);
ctx.lineTo(0,h);
ctx.lineTo(w,h);
ctx.lineTo(w,50);
ctx.lineTo(r,50);
ctx.bezierCurveTo((r-35),50,(r-70),0,(r-120),0);
ctx.bezierCurveTo((l+70),0,(l+49),50,l,50);
ctx.lineTo(0,50);
ctx.closePath();
ctx.clip();
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
ctx.restore();
}
function fitCanvasSize() {
canvas.width = document.body.clientWidth;
canvas.height = document.body.clientHeight;
}
window.addEventListener('resize', function () {
fitCanvasSize();
draw();
});
img.onload = function () {
draw();
}
fitCanvasSize();
img.src = 'https://placeholdit.imgix.net/~text?txtsize=28&txt=300%C3%97300&w=300&h=300';
编辑2,保持图片纵横比
为了保持图像的纵横比图像可以被切割和居中like here .为此,我们需要额外的变量:
var sx, sy, sWidth, sHeight;
var imgAspectRatio = img.width / img.height;
var areaAspectRatio = w / h;
sx, sx, sWidth, sHeight
的用途在 MDN 中有解释。
sx: The X coordinate of the top left corner of the sub-rectangle of the source image to draw into the destination context.
sy: The Y coordinate of the top left corner of the sub-rectangle of the source image to draw into the destination context.
sWidth: The width of the sub-rectangle of the source image to draw into the destination context. If not specified, the entire rectangle from the coordinates specified by sx and sy to the bottom-right corner of the image is used.
sHeight: The height of the sub-rectangle of the source image to draw into the destination context.
以下是默认值,如果 imgAspectRatio 等于 areaAspectRatio,这些值将保持不变:
sx = 0;
sy = 0;
sWidth = img.width;
sHeight = img.height;
否则:
if (imgAspectRatio > areaAspectRatio) {
// image is centered horizontally
sWidth = (areaAspectRatio / imgAspectRatio) * img.width;
sx = (img.width - sWidth ) / 2;
} else if (imgAspectRatio < areaAspectRatio) {
// image is centered vertically
sHeight = (imgAspectRatio / areaAspectRatio) * img.height;
sy = (img.height - sHeight) / 2;
}
下一张画图:
ctx.drawImage(img, sx, sy, sWidth, sHeight, 0, 0, canvas.width, canvas.height);
最终代码:
var canvas = document.getElementById('slide');
var ctx = canvas.getContext('2d');
var img = new Image();
function draw() {
var w = canvas.width;
var h = canvas.height;
var sx, sy, sWidth, sHeight;
var imgAspectRatio = img.width / img.height;
var areaAspectRatio = w / h;
// below values remains unchanged if
// image aspect ratio === area aspect ratio
sx = 0;
sy = 0;
sWidth = img.width;
sHeight = img.height;
if (imgAspectRatio > areaAspectRatio) {
// image is centered horizontally
sWidth = (areaAspectRatio / imgAspectRatio) * img.width;
sx = (img.width - sWidth ) / 2;
} else if (imgAspectRatio < areaAspectRatio) {
// image is centered vertically
sHeight = (imgAspectRatio / areaAspectRatio) * img.height;
sy = (img.height - sHeight) / 2;
}
var l = w/2 - 120;
var r = w/2 + 120;
ctx.save();
ctx.beginPath();
ctx.moveTo(0,50);
ctx.lineTo(0,h);
ctx.lineTo(w,h);
ctx.lineTo(w,50);
ctx.lineTo(r,50);
ctx.bezierCurveTo((r-35),50,(r-70),0,(r-120),0);
ctx.bezierCurveTo((l+70),0,(l+49),50,l,50);
ctx.lineTo(0,50);
ctx.closePath();
ctx.clip();
ctx.drawImage(img, sx, sy, sWidth, sHeight, 0, 0, canvas.width, canvas.height);
ctx.restore();
}
function fitCanvasSize() {
canvas.width = document.body.clientWidth;
canvas.height = document.body.clientHeight;
}
window.addEventListener('resize', function () {
fitCanvasSize();
draw();
});
img.onload = function () {
draw();
}
fitCanvasSize();
img.src = 'http://upload.wikimedia.org/wikipedia/commons/3/3f/Brown-bear-in-spring.jpg';
更简单的方法是保持 Canvas 纵横比而不是剪切图像。
此示例有效,因为 Canvas 是裁剪区域的边界框。 如果裁剪区域与 Canvas 相比较小,则:
the image will "float" around the clipped area (see markE comment)
如果有人要求,我可以写出这个问题的解决方案。
关于javascript - 使用图案覆盖 Canvas 中的路径,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30664430/