我想用一些文字覆盖背景图片，在Fabric.js中是否有办法模糊背景，以便文字更具可读性？
我尝试过滤镜，但只能将背景图像更改为灰度，模糊似乎没有任何效果。
提前致谢。
答案 0 :(得分：0)
可能是滤镜模糊： https://developer.mozilla.org/fr/docs/Web/API/CanvasRenderingContext2D/filter
示例：http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
答案 1 :(得分：0)
我创建了这个要点，它添加了叠加模糊作为结构类的过滤器。
https://gist.github.com/human-a/25b7f58565b89de4e999ef2f4de1982c
/**
* Stack blur filter for fabricjs
* Example:
* obj.filters.push(new fabric.Image.filters.StackBlur(6));
* obj.applyFilters(canvas.renderAll.bind(canvas));
*
* Heavily inspired by:
* https://gist.github.com/pierrickouw/2ab679159beee9d80ca6
* http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
* uses stackBlurCanvasRGBA function but could be swapped be stackBlurCanvasRGB
* @see: http://www.quasimondo.com/StackBlurForCanvas/StackBlur.js
*/
(function() {
var fabric = window.fabric,
extend = fabric.util.object.extend;
var mul_table = [
512,512,456,512,328,456,335,512,405,328,271,456,388,335,292,512,
454,405,364,328,298,271,496,456,420,388,360,335,312,292,273,512,
482,454,428,405,383,364,345,328,312,298,284,271,259,496,475,456,
437,420,404,388,374,360,347,335,323,312,302,292,282,273,265,512,
497,482,468,454,441,428,417,405,394,383,373,364,354,345,337,328,
320,312,305,298,291,284,278,271,265,259,507,496,485,475,465,456,
446,437,428,420,412,404,396,388,381,374,367,360,354,347,341,335,
329,323,318,312,307,302,297,292,287,282,278,273,269,265,261,512,
505,497,489,482,475,468,461,454,447,441,435,428,422,417,411,405,
399,394,389,383,378,373,368,364,359,354,350,345,341,337,332,328,
324,320,316,312,309,305,301,298,294,291,287,284,281,278,274,271,
268,265,262,259,257,507,501,496,491,485,480,475,470,465,460,456,
451,446,442,437,433,428,424,420,416,412,408,404,400,396,392,388,
385,381,377,374,370,367,363,360,357,354,350,347,344,341,338,335,
332,329,326,323,320,318,315,312,310,307,304,302,299,297,294,292,
289,287,285,282,280,278,275,273,271,269,267,265,263,261,259
];
var shg_table = [
9, 11, 12, 13, 13, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 17,
17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, 18, 18, 19,
19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 20, 20, 20,
20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 21,
21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
21, 21, 21, 21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22,
22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, 23,
23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23, 23,
23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24
];
function BlurStack() {
this.r = 0;
this.g = 0;
this.b = 0;
this.a = 0;
this.next = null;
}
fabric.Image.filters.StackBlur = fabric.util.createClass(fabric.Image.filters.BaseFilter,{
/**
* Filter type
*/
type: 'StackBlur',
/**
* Constructor
*/
initialize: function(radius) { //radius of the blur
this.radius = radius || 0;
if(this.radius > 180) {
this.radius = 180;
}
if(this.radius < 1) {
this.radius = 0;
}
},
/**
* Applies blur to canvas element
*/
applyTo: function(canvas) {
// Don't apply blur if it's zero
if (!this.radius) return;
var radius = this.radius;
var width = canvas.width;
var height = canvas.height;
var context = canvas.getContext("2d");
var imageData;
imageData = context.getImageData( 0, 0, width, height );
var pixels = imageData.data;
var x, y, i, p, yp, yi, yw, r_sum, g_sum, b_sum, a_sum,
r_out_sum, g_out_sum, b_out_sum, a_out_sum,
r_in_sum, g_in_sum, b_in_sum, a_in_sum,
pr, pg, pb, pa, rbs;
var div = radius + radius + 1;
var widthMinus1 = width - 1;
var heightMinus1 = height - 1;
var radiusPlus1 = radius + 1;
var sumFactor = radiusPlus1 * ( radiusPlus1 + 1 ) / 2;
var stackStart = new BlurStack();
var stack = stackStart;
for ( i = 1; i < div; i++ ) {
stack = stack.next = new BlurStack();
if ( i === radiusPlus1 ) var stackEnd = stack;
}
stack.next = stackStart;
var stackIn = null;
var stackOut = null;
yw = yi = 0;
var mul_sum = mul_table[radius];
var shg_sum = shg_table[radius];
for ( y = 0; y < height; y++ ) {
r_in_sum = g_in_sum = b_in_sum = a_in_sum = r_sum = g_sum = b_sum = a_sum = 0;
r_out_sum = radiusPlus1 * ( pr = pixels[yi] );
g_out_sum = radiusPlus1 * ( pg = pixels[yi+1] );
b_out_sum = radiusPlus1 * ( pb = pixels[yi+2] );
a_out_sum = radiusPlus1 * ( pa = pixels[yi+3] );
r_sum += sumFactor * pr;
g_sum += sumFactor * pg;
b_sum += sumFactor * pb;
a_sum += sumFactor * pa;
stack = stackStart;
for( i = 0; i < radiusPlus1; i++ ) {
stack.r = pr;
stack.g = pg;
stack.b = pb;
stack.a = pa;
stack = stack.next;
}
for( i = 1; i < radiusPlus1; i++ ) {
p = yi + (( widthMinus1 < i ? widthMinus1 : i ) << 2 );
r_sum += ( stack.r = ( pr = pixels[p])) * ( rbs = radiusPlus1 - i );
g_sum += ( stack.g = ( pg = pixels[p+1])) * rbs;
b_sum += ( stack.b = ( pb = pixels[p+2])) * rbs;
a_sum += ( stack.a = ( pa = pixels[p+3])) * rbs;
r_in_sum += pr;
g_in_sum += pg;
b_in_sum += pb;
a_in_sum += pa;
stack = stack.next;
}
stackIn = stackStart;
stackOut = stackEnd;
for ( x = 0; x < width; x++ ) {
pixels[yi+3] = pa = (a_sum * mul_sum) >> shg_sum;
if ( pa !== 0 )
{
pa = 255 / pa;
pixels[yi] = ((r_sum * mul_sum) >> shg_sum) * pa;
pixels[yi+1] = ((g_sum * mul_sum) >> shg_sum) * pa;
pixels[yi+2] = ((b_sum * mul_sum) >> shg_sum) * pa;
} else {
pixels[yi] = pixels[yi+1] = pixels[yi+2] = 0;
}
r_sum -= r_out_sum;
g_sum -= g_out_sum;
b_sum -= b_out_sum;
a_sum -= a_out_sum;
r_out_sum -= stackIn.r;
g_out_sum -= stackIn.g;
b_out_sum -= stackIn.b;
a_out_sum -= stackIn.a;
// eslint-disable-next-line
p = ( yw + ( ( p = x + radius + 1 ) < widthMinus1 ? p : widthMinus1 ) ) << 2;
r_in_sum += ( stackIn.r = pixels[p]);
g_in_sum += ( stackIn.g = pixels[p+1]);
b_in_sum += ( stackIn.b = pixels[p+2]);
a_in_sum += ( stackIn.a = pixels[p+3]);
r_sum += r_in_sum;
g_sum += g_in_sum;
b_sum += b_in_sum;
a_sum += a_in_sum;
stackIn = stackIn.next;
r_out_sum += ( pr = stackOut.r );
g_out_sum += ( pg = stackOut.g );
b_out_sum += ( pb = stackOut.b );
a_out_sum += ( pa = stackOut.a );
r_in_sum -= pr;
g_in_sum -= pg;
b_in_sum -= pb;
a_in_sum -= pa;
stackOut = stackOut.next;
yi += 4;
}
yw += width;
}
for ( x = 0; x < width; x++ ) {
g_in_sum = b_in_sum = a_in_sum = r_in_sum = g_sum = b_sum = a_sum = r_sum = 0;
yi = x << 2;
r_out_sum = radiusPlus1 * ( pr = pixels[yi]);
g_out_sum = radiusPlus1 * ( pg = pixels[yi+1]);
b_out_sum = radiusPlus1 * ( pb = pixels[yi+2]);
a_out_sum = radiusPlus1 * ( pa = pixels[yi+3]);
r_sum += sumFactor * pr;
g_sum += sumFactor * pg;
b_sum += sumFactor * pb;
a_sum += sumFactor * pa;
stack = stackStart;
for( i = 0; i < radiusPlus1; i++ )
{
stack.r = pr;
stack.g = pg;
stack.b = pb;
stack.a = pa;
stack = stack.next;
}
yp = width;
for( i = 1; i <= radius; i++ )
{
yi = ( yp + x ) << 2;
r_sum += ( stack.r = ( pr = pixels[yi])) * ( rbs = radiusPlus1 - i );
g_sum += ( stack.g = ( pg = pixels[yi+1])) * rbs;
b_sum += ( stack.b = ( pb = pixels[yi+2])) * rbs;
a_sum += ( stack.a = ( pa = pixels[yi+3])) * rbs;
r_in_sum += pr;
g_in_sum += pg;
b_in_sum += pb;
a_in_sum += pa;
stack = stack.next;
if( i < heightMinus1 )
{
yp += width;
}
}
yi = x;
stackIn = stackStart;
stackOut = stackEnd;
for ( y = 0; y < height; y++ )
{
p = yi << 2;
pixels[p+3] = pa = (a_sum * mul_sum) >> shg_sum;
if ( pa > 0 )
{
pa = 255 / pa;
pixels[p] = ((r_sum * mul_sum) >> shg_sum ) * pa;
pixels[p+1] = ((g_sum * mul_sum) >> shg_sum ) * pa;
pixels[p+2] = ((b_sum * mul_sum) >> shg_sum ) * pa;
} else {
pixels[p] = pixels[p+1] = pixels[p+2] = 0;
}
r_sum -= r_out_sum;
g_sum -= g_out_sum;
b_sum -= b_out_sum;
a_sum -= a_out_sum;
r_out_sum -= stackIn.r;
g_out_sum -= stackIn.g;
b_out_sum -= stackIn.b;
a_out_sum -= stackIn.a;
// eslint-disable-next-line
p = ( x + (( ( p = y + radiusPlus1) < heightMinus1 ? p : heightMinus1 ) * width )) << 2;
r_sum += ( r_in_sum += ( stackIn.r = pixels[p]));
g_sum += ( g_in_sum += ( stackIn.g = pixels[p+1]));
b_sum += ( b_in_sum += ( stackIn.b = pixels[p+2]));
a_sum += ( a_in_sum += ( stackIn.a = pixels[p+3]));
stackIn = stackIn.next;
r_out_sum += ( pr = stackOut.r );
g_out_sum += ( pg = stackOut.g );
b_out_sum += ( pb = stackOut.b );
a_out_sum += ( pa = stackOut.a );
r_in_sum -= pr;
g_in_sum -= pg;
b_in_sum -= pb;
a_in_sum -= pa;
stackOut = stackOut.next;
yi += width;
}
}
context.putImageData( imageData, 0, 0 );
},
/**
* Returns object representation of an instance
*/
toObject: function() {
return extend(this.callSuper('toObject'), {
radius: this.radius
});
}
});
fabric.Image.filters.StackBlur.fromObject = function(object) {
return new fabric.Image.filters.StackBlur(object);
};
})()