Comments: This article mainly introduces the example of using canvas to implement the scratch Effect of html5. For more information, see.
The coating automatically adapts to the size of the new image when img. src is modified.
Modify the layer function to change the coating style.
The following is the HTML source code (supported by mobile devices ):
The Code is as follows:
<! DOCTYPE html>
<Html>
<Body>
<Canvas/>
<Script>
(Function (bodyStyle ){
BodyStyle. Required userselect = 'none ';
BodyStyle. webkitUserSelect = 'none ';
Var img = new Image ();
Var canvas = document. querySelector ('canvas ');
Canvas. style. backgroundColor = 'transparent ';
Canvas. style. position = 'absolute ';
Img. addEventListener ('load', function (e ){
Var ctx;
Var w = img. width,
H = img. height;
Var offsetX = canvas. offsetLeft,
OffsetY = canvas. offsetTop;
Var mousedown = false;
Function layer (ctx ){
Ctx. fillStyle = 'Gray ';
Ctx. fillRect (0, 0, w, h );
}
Function eventDown (e ){
E. preventDefault ();
Mousedown = true;
}
Function eventUp (e ){
E. preventDefault ();
Mousedown = false;
}
Function eventMove (e ){
E. preventDefault ();
If (mousedown ){
If (e. changedTouches ){
E = e. changedTouches [e. changedTouches. length-1];
}
Var x = (e. clientX + document. body. scrollLeft | e. pageX)-offsetX | 0,
Y = (e. clientY + document. body. scrollTop | e. pageY)-offsetY | 0;
With (ctx ){
BeginPath ()
Arc (x, y, 5, 0, Math. PI * 2 );
Fill ();
}
}
}
Canvas. width = w;
Canvas. height = h;
Canvas. style. backgroundImage = 'url ('+ img. src + ')';
Ctx = canvas. getContext ('2d ');
Ctx. fillStyle = 'transparent ';
Ctx. fillRect (0, 0, w, h );
Layer (ctx );
Ctx. globalCompositeOperation = 'destination-out ';
Canvas. addEventListener ('touchstart', eventDown );
Canvas. addEventListener ('touchend', eventUp );
Canvas. addEventListener ('touchmove ', eventMove );
Canvas. addEventListener ('mousedown ', eventDown );
Canvas. addEventListener ('mouseup', eventUp );
Canvas. addEventListener ('mousemove ', eventMove );
});
Img. src = 'data: image/png; base64, expires + expires/expires + gDefUO4flpP56 // vv + 9693/3 u/hour + average/Xw + average/xtHWht7/p2Ip/Baidu/Bo/Vn9QgY + weight/zgan6Rx2X + cy9V6W + authorization + signature/Signature + 3XWTxIScO14J/5jpA2DHYkhXvVisWM/authorization + L + signature + + yAlyRxsI0/authorization + 7/authorization + signature/Signature + GHDjdC8eIY/authorization + Jgop + Signature /release/T + release + 2 release/release + 24bbg1wPfE + release + + qDvWixgT8ZI4H/zTQGgBG + release + z + release/VY4U + release/release /examples/templates + examples/samples/fKk/templates/CvI5V + examples + y4PFGZYg/samples + examples/templates + bMqqQY5S + examples/samples + DT6qUJBiNuHxBV5cN8CCM/templates + MI8Ez + kernel + a5YX/kernel/SHSsPLf/NKW/kernel + kernel/z6lw + kernel + 3nht5 + P + kernel/vcqL/kernel + z21I3t0inVGaIe6AXpqTo/ release/release + release/LZ3tONvYm5x/l + E + Ekhlc9cyc5 + release/PJN/release ++ release + release/Y + utaOVDVh/a4yvKsQYrn/3cz + 383667j/release + release/BpiARkxL/M9ODO4aGNN + rGiHfbeaYWK/release + release/r/release + release/HL + V7cQp74Ya/EqSt0Pzy2y + release /clusters/packages/5K7ZWF3bwOx + packages + I2HpqfssIVqz + packages/packages + downloads/downloads + FMPzbDjAco + logs/XZAKJ89h1Ht + downloads /Qv + examples/examples + examples/JOw + examples/Uu40t/examples/B7ylwC/EDTM/+ examples + vSWvPCN1GPHbXvaK9Ry/examples/JdD6LFS/ listen + Z58Q + DYnti7UtxkOoyf/weight + weight/weight + dw6kp/pWXX5 + V4vKAVWv + PqCgZTjMWU/y/kV1qIqOF/weight/ub2aboj/Weight = ';
}) (Document. body. style );
</Script>
</Body>
</Html>
You need to determine whether to use this code to replace the eventUp event handler function of the original code when it is finished:
The Code is as follows:
E. preventDefault ();
Mousedown = false;
Var data = ctx. getImageData (0, 0, w, h). data;
For (var I = 0, j = 0; I <data. length; I ++ = 4 ){
If (data [I] & data [I + 1] & data [I + 2] & data [I + 3]) {
J ++;
}
}
If (j <= w * h * 0.1 ){
Alert ('OK ');
}
In this Code, 0.1 means 10%. When the area of the coating is less than or equal to 10%, a window is displayed, indicating that the coating is finished and can be adjusted as needed.
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