我有这个fiddle，我需要知道我的网格始终从哪里开始的位置;
我可以缩放甚至拖放网格。
<!DOCTYPE html>
<!-- saved from url=(0048)http://phrogz.net/tmp/canvas_zoom_to_cursor.html -->
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Zooming via HTML5 Canvas Context</title>
<style type="text/css" media="screen">
body { background:#eee; margin:1em; text-align:center; }
canvas { display:block; margin:1em auto; background:#fff; border:1px solid #ccc }
</style>
</head>
<body style="-webkit-user-select: none;">
<canvas width="800" height="600"></canvas>
<script type="text/javascript" charset="utf-8">
var start_x = start_y = position_x = position_y = 50;
var canvas = document.getElementsByTagName('canvas')[0];
canvas.width = 800;
canvas.height = 600;
var gkhead = new Image;
var ball = new Image;
var square_size = 10;
window.onload = function() {
var ctx = canvas.getContext('2d');
trackTransforms(ctx);
function redraw() {
// Clear the entire canvas
var p1 = ctx.transformedPoint(0, 0);
var p2 = ctx.transformedPoint(canvas.width, canvas.height);
ctx.clearRect(p1.x, p1.y, p2.x - p1.x, p2.y - p1.y);
ctx.drawImage(gkhead, 50, 50);//punct stanga sus imagine cu marton
//console.log(ctx);
color = 'ff0000';
w = gkhead.width;
//console.log(w);
h = gkhead.height;
//console.log(h);
var i = 0;
i = i + 1;
if (i == 1)
color = 'ff0000';
if (i == 2)
color = '00ff00';
if (i == 3) {
color = '0000ff';
i = 0;
}
ctx.beginPath();
ctx.rect(50, 50, gkhead.width, gkhead.height);
ctx.lineWidth = 1;
ctx.strokeStyle = "#" + color;
ctx.stroke();
ctx.beginPath();
ctx.rect(51, 51, 8, 8);
ctx.lineWidth = 1;
ctx.fillStyle="#ffff00";
ctx.fill();
ctx.strokeStyle = "#ffff00";
ctx.stroke();
var ind = 0;
for (var j = 0; j < gkhead.width - square_size; j = j + square_size) {
ind++;
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'black';
ctx.moveTo(50 + (ind * square_size), 50);
ctx.lineTo(50 + (ind * square_size), 50 + gkhead.height);
ctx.stroke();
}
var ind = 0;
for (var j = 0; j < gkhead.height - square_size; j = j + square_size) {
ind++;
ctx.beginPath();
ctx.lineWidth = 1;
ctx.strokeStyle = 'blue';
ctx.moveTo(50, 50 + (ind * square_size));
ctx.lineTo(50 + gkhead.width, 50 + (ind * square_size));
ctx.stroke();
}
ctx.save();
ctx.translate(438.5, 223);
ctx.strokeStyle = '#06c';
ctx.beginPath();
ctx.lineWidth = 0.05;
for (var i = 0; i < 60; ++i) {
ctx.rotate(6 * i * Math.PI / 180);
ctx.moveTo(9, 0);
ctx.lineTo(10, 0);
ctx.rotate(-6 * i * Math.PI / 180);
}
ctx.stroke();
ctx.restore();
}
redraw();
var lastX = canvas.width / 2, lastY = canvas.height / 2;
var dragStart, dragged;
canvas.addEventListener('mousedown', function(evt) {
document.body.style.mozUserSelect = document.body.style.webkitUserSelect = document.body.style.userSelect = 'none';
lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
console.log('mousedown' + ' ' + lastX + ' ' + lastY);
dragStart = ctx.transformedPoint(lastX, lastY);
dragged = false;
}, false);
canvas.addEventListener('mousemove', function(evt) {
lastX = evt.offsetX || (evt.pageX - canvas.offsetLeft);
lastY = evt.offsetY || (evt.pageY - canvas.offsetTop);
dragged = true;
if (dragStart) {
var pt = ctx.transformedPoint(lastX, lastY);
ctx.translate(pt.x - dragStart.x, pt.y - dragStart.y);
console.log('dragStart: ' + ' ' + dragStart.x + ' ' + dragStart.y);
console.log('mousemove dragStart' + ' ' + (lastX) + ' ' + (lastY));
if (lastX != start_x) {
if (lastX > start_x)
position_x = position_x + lastX - start_x;
else
position_x = position_x + start_x - lastX;
}
if (lastY != start_y) {
if (lastY > start_y)
position_y = position_y + lastY - start_y;
else
position_y = position_y + start_y - lastY;
}
console.log('position: ' + position_x + ' ' + position_y);
redraw();
}
}, false);
canvas.addEventListener('mouseup', function(evt) {
dragStart = null;
if (!dragged)
zoom(evt.shiftKey ? -1 : 1);
}, false);
var scaleFactor = 1.1;
var zoom = function(clicks) {
var pt = ctx.transformedPoint(lastX, lastY);
ctx.translate(pt.x, pt.y);
var factor = Math.pow(scaleFactor, clicks);
ctx.scale(factor, factor);
ctx.translate(-pt.x, -pt.y);
redraw();
}
var handleScroll = function(evt) {
var delta = evt.wheelDelta ? evt.wheelDelta / 40 : evt.detail ? -evt.detail : 0;
if (delta)
zoom(delta);
return evt.preventDefault() && false;
};
canvas.addEventListener('DOMMouseScroll', handleScroll, false);
canvas.addEventListener('mousewheel', handleScroll, false);
};
gkhead.src = 'http://www.william.ro/wp-content/uploads/2013/07/13.jpg';
ball.src = 'http://phrogz.net/tmp/alphaball.png';
// Adds ctx.getTransform() - returns an SVGMatrix
// Adds ctx.transformedPoint(x,y) - returns an SVGPoint
function trackTransforms(ctx) {
var svg = document.createElementNS("http://www.w3.org/2000/svg", 'svg');
var xform = svg.createSVGMatrix();
ctx.getTransform = function() {
return xform;
};
var savedTransforms = [];
var save = ctx.save;
ctx.save = function() {
savedTransforms.push(xform.translate(0, 0));
return save.call(ctx);
};
var restore = ctx.restore;
ctx.restore = function() {
xform = savedTransforms.pop();
return restore.call(ctx);
};
var scale = ctx.scale;
ctx.scale = function(sx, sy) {
xform = xform.scaleNonUniform(sx, sy);
return scale.call(ctx, sx, sy);
};
var rotate = ctx.rotate;
ctx.rotate = function(radians) {
xform = xform.rotate(radians * 180 / Math.PI);
return rotate.call(ctx, radians);
};
var translate = ctx.translate;
ctx.translate = function(dx, dy) {
xform = xform.translate(dx, dy);
return translate.call(ctx, dx, dy);
};
var transform = ctx.transform;
ctx.transform = function(a, b, c, d, e, f) {
var m2 = svg.createSVGMatrix();
m2.a = a;
m2.b = b;
m2.c = c;
m2.d = d;
m2.e = e;
m2.f = f;
xform = xform.multiply(m2);
return transform.call(ctx, a, b, c, d, e, f);
};
var setTransform = ctx.setTransform;
ctx.setTransform = function(a, b, c, d, e, f) {
xform.a = a;
xform.b = b;
xform.c = c;
xform.d = d;
xform.e = e;
xform.f = f;
return setTransform.call(ctx, a, b, c, d, e, f);
};
var pt = svg.createSVGPoint();
ctx.transformedPoint = function(x, y) {
pt.x = x;
pt.y = y;
return pt.matrixTransform(xform.inverse());
}
}
</script>
</body>
</html>
答案 0 :(得分：6)
您可以通过这种方式获取相对于画布的鼠标坐标（与mousemove事件一起使用以检测鼠标是否在内部）：
canvas.onmousemove = function(e) {
var pos = getMousePos(this, e), /// provide this canvas and event
x = pos.x,
y = pos.y;
/// check x and y against the grid
}
/// the main function
function getMousePos(canvas, e) {
/// getBoundingClientRect is supported in most browsers and gives you
/// the absolute geometry of an element
var rect = canvas.getBoundingClientRect();
/// as mouse event coords are relative to document you need to
/// subtract the element's left and top position:
return {x: e.clientX - rect.left, y: e.clientY - rect.top};
}
或者可选：
canvas.addEventListener('mousemove', function(e) {
var pos = getMousePos(canvas, e), /// provide this canvas and event
x = pos.x,
y = pos.y;
/// check x and y against the grid
}, false);
function getMousePos(canvas, e) {
var rect = canvas.getBoundingClientRect();
return {x: e.clientX - rect.left, y: e.clientY - rect.top};
}