在html5的画布上绘制扭曲的图像

Question

是否有可能，如果是这样，如何绘制图像，其四个角被扭曲为非矩形形状。例如，如果您想要绘制图像，就好像它已经在3d空间中旋转一样。

Answer 1

我基于Thatcher Ulrich的代码（http://tulrich.com/geekstuff/canvas/perspective.html）创建了一个简单的4点变换。这个版本只是提取一小部分三角形代码并处理几何细分以进行适当的转换。享受！

http://jsfiddle.net/mrbendel/6rbtde5t/1/

var controls = [];
var canvas;
var context;
var image;
var triangles = [];
var dirtyTriangles = true;

var rand = function(s,e) {
    return Math.random() * (e-s) + s;
}

// dom ready
$(document).ready(function() {
    image = new Image();
    $(image).load(function() {
        setInterval(draw, 1000 / 60);
    });
    $(image).attr('src', 'http://media.giphy.com/media/NWb6sWXQQTqwg/giphy.gif');

    canvas = document.createElement('canvas');
    $(canvas).attr('width', 500);
    $(canvas).attr('height', 500);
    $('body').append(canvas);

    context = canvas.getContext('2d');

    //
    for (var i = 0; i < 4; ++i) {
        var control = document.createElement('div');
        $(control).addClass('node');
        $('body').append(control);
        controls.push(control);
    }

    $(controls[0]).css('left', rand(25, 225));
    $(controls[0]).css('top', rand(25, 225));

    $(controls[1]).css('left', rand(250, 475));
    $(controls[1]).css('top', rand(25, 225));

    $(controls[2]).css('left', rand(250, 475));
    $(controls[2]).css('top', rand(250, 475));

    $(controls[3]).css('left', rand(25, 225));
    $(controls[3]).css('top', rand(250, 475));

    $('body').mousedown(function(e) {
        if ($(e.target).hasClass('node')) {
            var node = e.target;

            $('body').mousemove(function(e) {
                var x = e.pageX;
                var y = e.pageY;
                $(node).css('left', x);
                $(node).css('top', y);
                dirtyTriangles = true;
            });

            $('body').mouseup(function(e) {
                $('body').off( "mousemove" );
                $('body').off( "mouseup" );
            });
        }
    });
});

var draw = function() {
    context.clearRect(0,0,500,500);

    var render = function(wireframe, image, tri) {

        if (wireframe) {
            context.strokeStyle = "black";
            context.beginPath();
            context.moveTo(tri.p0.x, tri.p0.y);
            context.lineTo(tri.p1.x, tri.p1.y);
            context.lineTo(tri.p2.x, tri.p2.y);
            context.lineTo(tri.p0.x, tri.p0.y);
            context.stroke();
            context.closePath();
        }

        if (image) {
            drawTriangle(context, image,
                         tri.p0.x, tri.p0.y,
                         tri.p1.x, tri.p1.y,
                         tri.p2.x, tri.p2.y,
                         tri.t0.u, tri.t0.v,
                         tri.t1.u, tri.t1.v,
                         tri.t2.u, tri.t2.v);
        }
    }

    if (dirtyTriangles) {
        dirtyTriangles = false;
        calculateGeometry();
    }

    for (triangle of triangles) {
        render(true, image, triangle);
    }
}

var calculateGeometry = function() {
    // clear triangles out
    triangles = [];

    // generate subdivision
    var subs = 7; // vertical subdivisions
    var divs = 7; // horizontal subdivisions

    var p1 = new Point(parseInt($(controls[0]).css('left')) + 6, parseInt($(controls[0]).css('top')) + 6);
    var p2 = new Point(parseInt($(controls[1]).css('left')) + 6, parseInt($(controls[1]).css('top')) + 6);
    var p3 = new Point(parseInt($(controls[2]).css('left')) + 6, parseInt($(controls[2]).css('top')) + 6);
    var p4 = new Point(parseInt($(controls[3]).css('left')) + 6, parseInt($(controls[3]).css('top')) + 6);

    var dx1 = p4.x - p1.x;
    var dy1 = p4.y - p1.y;
    var dx2 = p3.x - p2.x;
    var dy2 = p3.y - p2.y;

    var imgW = image.naturalWidth;
    var imgH = image.naturalHeight;

    for (var sub = 0; sub < subs; ++sub) {
        var curRow = sub / subs;
        var nextRow = (sub + 1) / subs;

        var curRowX1 = p1.x + dx1 * curRow;
        var curRowY1 = p1.y + dy1 * curRow;

        var curRowX2 = p2.x + dx2 * curRow;
        var curRowY2 = p2.y + dy2 * curRow;

        var nextRowX1 = p1.x + dx1 * nextRow;
        var nextRowY1 = p1.y + dy1 * nextRow;

        var nextRowX2 = p2.x + dx2 * nextRow;
        var nextRowY2 = p2.y + dy2 * nextRow;

        for (var div = 0; div < divs; ++div) {
            var curCol = div / divs;
            var nextCol = (div + 1) / divs;

            var dCurX = curRowX2 - curRowX1;
            var dCurY = curRowY2 - curRowY1;
            var dNextX = nextRowX2 - nextRowX1;
            var dNextY = nextRowY2 - nextRowY1;

            var p1x = curRowX1 + dCurX * curCol;
            var p1y = curRowY1 + dCurY * curCol;

            var p2x = curRowX1 + (curRowX2 - curRowX1) * nextCol;
            var p2y = curRowY1 + (curRowY2 - curRowY1) * nextCol;

            var p3x = nextRowX1 + dNextX * nextCol;
            var p3y = nextRowY1 + dNextY * nextCol;

            var p4x = nextRowX1 + dNextX * curCol;
            var p4y = nextRowY1 + dNextY * curCol;

            var u1 = curCol * imgW;
            var u2 = nextCol * imgW;
            var v1 = curRow * imgH;
            var v2 = nextRow * imgH;

            var triangle1 = new Triangle(
                new Point(p1x, p1y),
                new Point(p3x, p3y),
                new Point(p4x, p4y),
                new TextCoord(u1, v1),
                new TextCoord(u2, v2),
                new TextCoord(u1, v2)
            );

            var triangle2 = new Triangle(
                new Point(p1x, p1y),
                new Point(p2x, p2y),
                new Point(p3x, p3y),
                new TextCoord(u1, v1),
                new TextCoord(u2, v1),
                new TextCoord(u2, v2)
            );

            triangles.push(triangle1);
            triangles.push(triangle2);
        }
    }
}

// from http://tulrich.com/geekstuff/canvas/jsgl.js
var drawTriangle = function(ctx, im, x0, y0, x1, y1, x2, y2,
    sx0, sy0, sx1, sy1, sx2, sy2) {
    ctx.save();

    // Clip the output to the on-screen triangle boundaries.
    ctx.beginPath();
    ctx.moveTo(x0, y0);
    ctx.lineTo(x1, y1);
    ctx.lineTo(x2, y2);
    ctx.closePath();
    //ctx.stroke();//xxxxxxx for wireframe
    ctx.clip();

    /*
    ctx.transform(m11, m12, m21, m22, dx, dy) sets the context transform matrix.

    The context matrix is:

    [ m11 m21 dx ]
    [ m12 m22 dy ]
    [  0   0   1 ]

    Coords are column vectors with a 1 in the z coord, so the transform is:
    x_out = m11 * x + m21 * y + dx;
    y_out = m12 * x + m22 * y + dy;

    From Maxima, these are the transform values that map the source
    coords to the dest coords:

    sy0 (x2 - x1) - sy1 x2 + sy2 x1 + (sy1 - sy2) x0
    [m11 = - -----------------------------------------------------,
    sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

    sy1 y2 + sy0 (y1 - y2) - sy2 y1 + (sy2 - sy1) y0
    m12 = -----------------------------------------------------,
    sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

    sx0 (x2 - x1) - sx1 x2 + sx2 x1 + (sx1 - sx2) x0
    m21 = -----------------------------------------------------,
    sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

    sx1 y2 + sx0 (y1 - y2) - sx2 y1 + (sx2 - sx1) y0
    m22 = - -----------------------------------------------------,
    sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

    sx0 (sy2 x1 - sy1 x2) + sy0 (sx1 x2 - sx2 x1) + (sx2 sy1 - sx1 sy2) x0
    dx = ----------------------------------------------------------------------,
    sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

    sx0 (sy2 y1 - sy1 y2) + sy0 (sx1 y2 - sx2 y1) + (sx2 sy1 - sx1 sy2) y0
    dy = ----------------------------------------------------------------------]
    sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0
  */

    // TODO: eliminate common subexpressions.
    var denom = sx0 * (sy2 - sy1) - sx1 * sy2 + sx2 * sy1 + (sx1 - sx2) * sy0;
    if (denom == 0) {
        return;
    }
    var m11 = -(sy0 * (x2 - x1) - sy1 * x2 + sy2 * x1 + (sy1 - sy2) * x0) / denom;
    var m12 = (sy1 * y2 + sy0 * (y1 - y2) - sy2 * y1 + (sy2 - sy1) * y0) / denom;
    var m21 = (sx0 * (x2 - x1) - sx1 * x2 + sx2 * x1 + (sx1 - sx2) * x0) / denom;
    var m22 = -(sx1 * y2 + sx0 * (y1 - y2) - sx2 * y1 + (sx2 - sx1) * y0) / denom;
    var dx = (sx0 * (sy2 * x1 - sy1 * x2) + sy0 * (sx1 * x2 - sx2 * x1) + (sx2 * sy1 - sx1 * sy2) * x0) / denom;
    var dy = (sx0 * (sy2 * y1 - sy1 * y2) + sy0 * (sx1 * y2 - sx2 * y1) + (sx2 * sy1 - sx1 * sy2) * y0) / denom;

    ctx.transform(m11, m12, m21, m22, dx, dy);

    // Draw the whole image.  Transform and clip will map it onto the
    // correct output triangle.
    //
    // TODO: figure out if drawImage goes faster if we specify the rectangle that
    // bounds the source coords.
    ctx.drawImage(im, 0, 0);
    ctx.restore();
};

// point class

var Point = function(x,y) {
    this.x = x?x:0;
    this.y = y?y:0;
}

var p = Point.prototype;

p.length = function(point) {
    point = point?point:new Point();
    var xs =0, ys =0;
    xs = point.x - this.x;
    xs = xs * xs;

    ys = point.y - this.y;
    ys = ys * ys;
    return Math.sqrt( xs + ys );
}

var TextCoord = function(u,v) {
    this.u = u?u:0;
    this.v = v?v:0;
}

var Triangle = function(p0, p1, p2, t0, t1, t2) {
    this.p0 = p0;
    this.p1 = p1;
    this.p2 = p2;

    this.t0 = t0;
    this.t1 = t1;
    this.t2 = t2;
}

Answer 2

最简单的方法是在绘制图像之前将转换应用于画布。

http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#transformations

通过倾斜变换，您可以使其看起来像是以透视方式绘制的

这是一个非常简单的例子：

ctx.setTransform (1, -0.2, 0, 1, 0, 0);
ctx.drawImage(blah);

Answer 3

查看本教程，它使用光学错觉来模拟透视。 http://www.subshell.com/en/subshell/blog/image-manipulation-html5-canvas102.html

Answer 4

您可以尝试function transferPoint (xI, yI, source, destination)已解除here。

源和目标是源和目标矩形的四个点。该代码适用于（SVG）路径坐标（曲线和直线），但经过一些修改也适用于像素。

Answer 5

上面的许多评论者都要求隐藏三角形-这样做会消失（有关信息：@ erbridge，@ ConstantinGroß）：

以下内容仍归@AndyPoes所有，因为这是他的全部建议-我只添加他建议的完整版本。

更改此行：

render(true, image, triangle);

对此：

render(false, image, triangle);

...黑色三角形将消失，但是您将看到三角形之间的间隙，因此现在执行以下操作：

更改此：

var triangle1 = new Triangle(
            new Point(p1x, p1y),
            new Point(p3x, p3y),
            new Point(p4x, p4y),
            new TextCoord(u1, v1),
            new TextCoord(u2, v2),
            new TextCoord(u1, v2)
        );

        var triangle2 = new Triangle(
            new Point(p1x, p1y),
            new Point(p2x, p2y),
            new Point(p3x, p3y),
            new TextCoord(u1, v1),
            new TextCoord(u2, v1),
            new TextCoord(u2, v2)
        );

为此：

            var triangle1 = new Triangle(
            new Point(p1x-1, p1y),
            new Point(p3x+2, p3y+1),
            new Point(p4x-1, p4y+1),
            new TextCoord(u1, v1),
            new TextCoord(u2, v2),
            new TextCoord(u1, v2)
        );

        var triangle2 = new Triangle(
            new Point(p1x-2, p1y),
            new Point(p2x+1, p2y),
            new Point(p3x+1, p3y+1),
            new TextCoord(u1, v1),
            new TextCoord(u2, v1),
            new TextCoord(u2, v2)
        );

....并且差距将会缩小。

新提琴= fiddler off the roof

完整代码在这里：

var controls = [];
var canvas;
var context;
var image;
var triangles = [];
var dirtyTriangles = false;

var rand = function(s,e) {
    return Math.random() * (e-s) + s;
}

// dom ready
$(document).ready(function() {
image = new Image();
$(image).load(function() {
    setInterval(draw, 1000 / 60);
});
$(image).attr('src', 'https://images.unsplash.com/photo-1500964757637-c85e8a162699?ixlib=rb-1.2.1&q=80&fm=jpg');

canvas = document.createElement('canvas');
$(canvas).attr('width', 500);
$(canvas).attr('height', 500);
$('body').append(canvas);

context = canvas.getContext('2d');

//
for (var i = 0; i < 4; ++i) {
    var control = document.createElement('div');
    $(control).addClass('node');
    $('body').append(control);
    controls.push(control);
}

$(controls[0]).css('left', rand(25, 225));
$(controls[0]).css('top', rand(25, 225));

$(controls[1]).css('left', rand(250, 475));
$(controls[1]).css('top', rand(25, 225));

$(controls[2]).css('left', rand(250, 475));
$(controls[2]).css('top', rand(250, 475));

$(controls[3]).css('left', rand(25, 225));
$(controls[3]).css('top', rand(250, 475));

$('body').mousedown(function(e) {
    if ($(e.target).hasClass('node')) {
        var node = e.target;

        $('body').mousemove(function(e) {
            var x = e.pageX;
            var y = e.pageY;
            $(node).css('left', x);
            $(node).css('top', y);
            dirtyTriangles = true;
        });

        $('body').mouseup(function(e) {
            $('body').off( "mousemove" );
            $('body').off( "mouseup" );
        });
    }
});
});

var draw = function() {
context.clearRect(0,0,500,500);

var render = function(wireframe, image, tri) {
    
    if (wireframe) {
        context.strokeStyle = "black";
        context.beginPath();
        context.moveTo(tri.p0.x, tri.p0.y);
        context.lineTo(tri.p1.x, tri.p1.y);
        context.lineTo(tri.p2.x, tri.p2.y);
        context.lineTo(tri.p0.x, tri.p0.y);
        context.stroke();
        context.closePath();
    }

    if (image) {
        drawTriangle(context, image,
                     tri.p0.x, tri.p0.y,
                     tri.p1.x, tri.p1.y,
                     tri.p2.x, tri.p2.y,
                     tri.t0.u, tri.t0.v,
                     tri.t1.u, tri.t1.v,
                     tri.t2.u, tri.t2.v);
    }
}

if (dirtyTriangles) {
    dirtyTriangles = false;
    calculateGeometry();
}

for (triangle of triangles) {
    render(true, image, triangle);
}
}

var calculateGeometry = function() {
// clear triangles out
triangles = [];

// generate subdivision
var subs = 7; // vertical subdivisions
var divs = 7; // horizontal subdivisions

var p1 = new Point(parseInt($(controls[0]).css('left')) + 6, parseInt($(controls[0]).css('top')) + 6);
var p2 = new Point(parseInt($(controls[1]).css('left')) + 6, parseInt($(controls[1]).css('top')) + 6);
var p3 = new Point(parseInt($(controls[2]).css('left')) + 6, parseInt($(controls[2]).css('top')) + 6);
var p4 = new Point(parseInt($(controls[3]).css('left')) + 6, parseInt($(controls[3]).css('top')) + 6);

var dx1 = p4.x - p1.x;
var dy1 = p4.y - p1.y;
var dx2 = p3.x - p2.x;
var dy2 = p3.y - p2.y;

var imgW = image.naturalWidth;
var imgH = image.naturalHeight;

for (var sub = 0; sub < subs; ++sub) {
    var curRow = sub / subs;
    var nextRow = (sub + 1) / subs;

    var curRowX1 = p1.x + dx1 * curRow;
    var curRowY1 = p1.y + dy1 * curRow;
    
    var curRowX2 = p2.x + dx2 * curRow;
    var curRowY2 = p2.y + dy2 * curRow;

    var nextRowX1 = p1.x + dx1 * nextRow;
    var nextRowY1 = p1.y + dy1 * nextRow;
    
    var nextRowX2 = p2.x + dx2 * nextRow;
    var nextRowY2 = p2.y + dy2 * nextRow;

    for (var div = 0; div < divs; ++div) {
        var curCol = div / divs;
        var nextCol = (div + 1) / divs;

        var dCurX = curRowX2 - curRowX1;
        var dCurY = curRowY2 - curRowY1;
        var dNextX = nextRowX2 - nextRowX1;
        var dNextY = nextRowY2 - nextRowY1;

        var p1x = curRowX1 + dCurX * curCol;
        var p1y = curRowY1 + dCurY * curCol;

        var p2x = curRowX1 + (curRowX2 - curRowX1) * nextCol;
        var p2y = curRowY1 + (curRowY2 - curRowY1) * nextCol;

        var p3x = nextRowX1 + dNextX * nextCol;
        var p3y = nextRowY1 + dNextY * nextCol;

        var p4x = nextRowX1 + dNextX * curCol;
        var p4y = nextRowY1 + dNextY * curCol;

        var u1 = curCol * imgW;
        var u2 = nextCol * imgW;
        var v1 = curRow * imgH;
        var v2 = nextRow * imgH;

        var triangle1 = new Triangle(
            new Point(p1x-1, p1y),
            new Point(p3x+2, p3y+1),
            new Point(p4x-1, p4y+1),
            new TextCoord(u1, v1),
            new TextCoord(u2, v2),
            new TextCoord(u1, v2)
        );

        var triangle2 = new Triangle(
            new Point(p1x-2, p1y),
            new Point(p2x+1, p2y),
            new Point(p3x+1, p3y+1),
            new TextCoord(u1, v1),
            new TextCoord(u2, v1),
            new TextCoord(u2, v2)
        );

        triangles.push(triangle1);
        triangles.push(triangle2);
    }
}
}

// from http://tulrich.com/geekstuff/canvas/jsgl.js
var drawTriangle = function(ctx, im, x0, y0, x1, y1, x2, y2,
sx0, sy0, sx1, sy1, sx2, sy2) {
ctx.save();

// Clip the output to the on-screen triangle boundaries.
ctx.beginPath();
ctx.moveTo(x0, y0);
ctx.lineTo(x1, y1);
ctx.lineTo(x2, y2);
ctx.closePath();
//ctx.stroke();//xxxxxxx for wireframe
ctx.clip();

/*
ctx.transform(m11, m12, m21, m22, dx, dy) sets the context transform matrix.

The context matrix is:

[ m11 m21 dx ]
[ m12 m22 dy ]
[  0   0   1 ]

Coords are column vectors with a 1 in the z coord, so the transform is:
x_out = m11 * x + m21 * y + dx;
y_out = m12 * x + m22 * y + dy;

From Maxima, these are the transform values that map the source
coords to the dest coords:

sy0 (x2 - x1) - sy1 x2 + sy2 x1 + (sy1 - sy2) x0
[m11 = - -----------------------------------------------------,
sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

sy1 y2 + sy0 (y1 - y2) - sy2 y1 + (sy2 - sy1) y0
m12 = -----------------------------------------------------,
sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

sx0 (x2 - x1) - sx1 x2 + sx2 x1 + (sx1 - sx2) x0
m21 = -----------------------------------------------------,
sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

sx1 y2 + sx0 (y1 - y2) - sx2 y1 + (sx2 - sx1) y0
m22 = - -----------------------------------------------------,
sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

sx0 (sy2 x1 - sy1 x2) + sy0 (sx1 x2 - sx2 x1) + (sx2 sy1 - sx1 sy2) x0
dx = ----------------------------------------------------------------------,
sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0

sx0 (sy2 y1 - sy1 y2) + sy0 (sx1 y2 - sx2 y1) + (sx2 sy1 - sx1 sy2) y0
dy = ----------------------------------------------------------------------]
sx0 (sy2 - sy1) - sx1 sy2 + sx2 sy1 + (sx1 - sx2) sy0
  */

// TODO: eliminate common subexpressions.
var denom = sx0 * (sy2 - sy1) - sx1 * sy2 + sx2 * sy1 + (sx1 - sx2) * sy0;
if (denom == 0) {
    return;
}
var m11 = -(sy0 * (x2 - x1) - sy1 * x2 + sy2 * x1 + (sy1 - sy2) * x0) / denom;
var m12 = (sy1 * y2 + sy0 * (y1 - y2) - sy2 * y1 + (sy2 - sy1) * y0) / denom;
var m21 = (sx0 * (x2 - x1) - sx1 * x2 + sx2 * x1 + (sx1 - sx2) * x0) / denom;
var m22 = -(sx1 * y2 + sx0 * (y1 - y2) - sx2 * y1 + (sx2 - sx1) * y0) / denom;
var dx = (sx0 * (sy2 * x1 - sy1 * x2) + sy0 * (sx1 * x2 - sx2 * x1) + (sx2 * sy1 - sx1 * sy2) * x0) / denom;
var dy = (sx0 * (sy2 * y1 - sy1 * y2) + sy0 * (sx1 * y2 - sx2 * y1) + (sx2 * sy1 - sx1 * sy2) * y0) / denom;

ctx.transform(m11, m12, m21, m22, dx, dy);

// Draw the whole image.  Transform and clip will map it onto the
// correct output triangle.
//
// TODO: figure out if drawImage goes faster if we specify the rectangle that
// bounds the source coords.
ctx.drawImage(im, 0, 0);
ctx.restore();
};

// point class

var Point = function(x,y) {
this.x = x?x:0;
this.y = y?y:0;
}

var p = Point.prototype;

p.length = function(point) {
    point = point?point:new Point();
    var xs =0, ys =0;
    xs = point.x - this.x;
    xs = xs * xs;

    ys = point.y - this.y;
    ys = ys * ys;
    return Math.sqrt( xs + ys );
}

var TextCoord = function(u,v) {
this.u = u?u:0;
this.v = v?v:0;
}

var Triangle = function(p0, p1, p2, t0, t1, t2) {
this.p0 = p0;
this.p1 = p1;
this.p2 = p2;

this.t0 = t0;
this.t1 = t1;
this.t2 = t2;
}