如何在缩放时绑定图像平移（HTML Canvas） [英] How to bound image pan when zooming (HTML Canvas)
本文介绍了如何在缩放时绑定图像平移（HTML Canvas）的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我试图限制边界，我遇到了问题。我从另一个画布上放大图像，然后实施缩放和平移。我的问题（下面的代码）是限制/限制offsetx / y，以便您永远不会看到空白;只有图像的一部分。
赦免混乱！任何帮助表示赞赏！ ：P
var zoomIntensity = 0.2; var canvas = document.getElementById（ var canvas =canvas）; var canvas2 = document.getElementById（canvas2）; var context = canvas.getContext（2d）; var context2 = canvas2.getContext（2d）; var width = 200; var height = 200; var scale = 1; var originx = 0; var originy = 0; var offset = {x：0，y：0}; //为（var x = 0; x <100; x ++）用随机像素填充小画布（var y = 0; y <100; y ++）{var rando = function（）{return Math.floor（Math.random（）* 9）}; var val = rando（）; context2.fillStyle =＃+ val + val + val; context2.fillRect（x，y，1,1）;} //绘制较大的canvas函数draw（）{context.imageSmoothingEnabled = false; //将屏幕清除为白色。 context.fillStyle =white; context.fillRect（originx - offset.x，originy - offset.y，width / scale，height / scale）; context.drawImage（canvas2,0,0，width，height）;} //在60FPS.setInterval（draw，1000/60）绘制循环; canvas.onmousewheel = function（event）{event.preventDefault（）; //获取鼠标偏移量。 var mousex = event.clientX - canvas.offsetLeft; var mousey = event.clientY - canvas.offsetTop; //将车轮标准化为+1或-1。 var wheel = event.wheelDelta / 120; //计算缩放因子。 var zoom = Math.exp（wheel * zoomIntensity）; //翻译所以可见原点位于上下文的原点。 context.translate（originx - offset.x，originy - offset.y）; // offset is panning //确保我们不会比正常缩放范围缩小var resultsScale = scale * zoom;如果（结果缩放比例<1）缩放比例= 1 /比例; //计算新的可见原点。最初鼠标距离角落的距离是鼠标/距离，我们希望鼠标下面的点在缩放后保持在同一个地方，但是这个//位于距离角落的鼠标/ new_scale处。因此，我们需要//移动原点（拐角的坐标）来解决这个问题。 originx - = mousex /（scale * zoom） - mousex / scale;原始 - =鼠标/（缩放*缩放） - 鼠标/缩放; //缩放（由于上面的转换，以原点为中心）。 context.scale（zoom，zoom）; //将可见原点偏移到适当的位置。 context.translate（-originx + offset.x，-originy + offset.y）; //偏移量正在平移//更新缩放比例等。 scale * = zoom;} document.onkeydown = function（evt）{var offsetx = 0; var offsety = 0; switch（evt.which）{case 37：// left offsetx = 1;打破;案例38：// up offsety = 1;打破;情况39：// right offsetx = -1 break;情况40：// down offsety = -1;打破; } offsetx / = scale; offsety / =规模; offset.x + = offsetx; offset.y + = offsety; context.translate（offsetx，offsety）;}
< canvas id =canvaswidth =200height =200>< / canvas>< canvas id =canvas2width =100height =100> code>
解决方案
一个视图
为了约束您需要将图像的角坐标转换为屏幕坐标的位置。由于在浏览器中实现转换仍然不是标准，所以下面的演示包含转换的副本。
对象视图保存画布视图。当您使用函数 view.setBounds（top，left，right，bottom）; 时，视图将被锁定到该区域（您正在查看的图像为0,0,100,100）
缩放和位置（原点）将被限制为保持边界在外部或由 view.setContext（context ）。
函数 scaleAt（pos，amount）; 指定的pos（例如鼠标位置）
要设置转换，使用 view.apply（），这将更新视图转换并设置上下文转换。
以下是其他一些可能很方便查看代码的函数。
演示使用鼠标点击拖动来平移和滚动以进行缩放。
演示是OP的示例宽度修改以复制问题的副本。
div {user-select：none;} / *鼠标阻止拖动选择内容* / canvas {border：2px solid black;}
< div>< canvas id =canvaswidth =200height =200>< / canvas>< canvas id =canvas2width =100height = 100>< / canvas>< p>鼠标滚轮进行缩放。 < / div>< / code>< / pre>< / div>< / div>< p>< p> >
I'm trying to limit boundaries and I'm running into issues. I'm upscaling an image from another canvas and then implementing zoom and pan. My issue (code below) is with limiting/capping the offsetx/y so that you never see the whitespace; only parts of the image.
Pardon the mess! Any help is appreciated! :P
var zoomIntensity = 0.2;
var canvas = document.getElementById("canvas");
var canvas2 = document.getElementById("canvas2");
var context = canvas.getContext("2d");
var context2 = canvas2.getContext("2d");
var width = 200;
var height = 200;
var scale = 1;
var originx = 0;
var originy = 0;
var offset = {x:0, y:0};
//fill smaller canvas with random pixels
for(var x = 0; x < 100; x++)
for(var y = 0; y < 100; y++)
{
var rando = function(){return Math.floor(Math.random() * 9)};
var val = rando();
context2.fillStyle = "#" + val + val + val;
context2.fillRect(x,y,1,1);
}
//draw the larger canvas
function draw()
{
context.imageSmoothingEnabled = false;
// Clear screen to white.
context.fillStyle = "white";
context.fillRect(originx - offset.x, originy - offset.y, width/scale, height/scale);
context.drawImage(canvas2, 0,0, width, height);
}
// Draw loop at 60FPS.
setInterval(draw, 1000/60);
canvas.onmousewheel = function (event){
event.preventDefault();
// Get mouse offset.
var mousex = event.clientX - canvas.offsetLeft;
var mousey = event.clientY - canvas.offsetTop;
// Normalize wheel to +1 or -1.
var wheel = event.wheelDelta/120;
// Compute zoom factor.
var zoom = Math.exp(wheel*zoomIntensity);
// Translate so the visible origin is at the context's origin.
context.translate(originx - offset.x, originy - offset.y); //offset is panning
//make sure we don't zoom out further than normal scale
var resultingScale = scale * zoom;
if(resultingScale < 1)
zoom = 1/scale;
// Compute the new visible origin. Originally the mouse is at a
// distance mouse/scale from the corner, we want the point under
// the mouse to remain in the same place after the zoom, but this
// is at mouse/new_scale away from the corner. Therefore we need to
// shift the origin (coordinates of the corner) to account for this.
originx -= mousex/(scale*zoom) - mousex/scale;
originy -= mousey/(scale*zoom) - mousey/scale;
// Scale it (centered around the origin due to the trasnslate above).
context.scale(zoom, zoom);
// Offset the visible origin to it's proper position.
context.translate(-originx + offset.x, -originy + offset.y); //offset is panning
// Update scale and others.
scale *= zoom;
}
document.onkeydown = function (evt)
{
var offsetx = 0;
var offsety = 0;
switch(evt.which)
{
case 37: //left
offsetx = 1;
break;
case 38: //up
offsety = 1;
break;
case 39: //right
offsetx = -1
break;
case 40: //down
offsety = -1;
break;
}
offsetx /= scale;
offsety /= scale;
offset.x += offsetx;
offset.y += offsety;
context.translate(offsetx,offsety);
}
<canvas id="canvas" width="200" height="200"></canvas>
<canvas id="canvas2" width="100" height="100"></canvas>
解决方案 Using transformation matrix to constrain a view
To constrain the position you need to transform the corner coordinates of the image to screen coordinates. As getting the transform is still not standard across browsers the demo below holds a copy of the transform.
The object view holds the canvas view. When you use the function view.setBounds(top,left,right,bottom); the view will be locked to that area (the image you are viewing 0,0,100,100)
The scale and position (origin) will be constrained to keep the bounds outside or one the edge of the canvas context set by view.setContext(context).
The function scaleAt(pos,amount); will scale at a specified pos (eg mouse position)
To set the transform use view.apply() this will update the view transform and set the context transform.
The are a few other functions that may prove handy see code.
Demo uses mouse click drag to pan and wheel to zoom.
Demo is a copy of the OP's example width modifications to answer question.
// use requestAnimationFrame when doing any form of animation via javascript
requestAnimationFrame(draw);
var zoomIntensity = 0.2;
var canvas = document.getElementById("canvas");
var canvas2 = document.getElementById("canvas2");
var context = canvas.getContext("2d");
var context2 = canvas2.getContext("2d");
var width = 200;
var height = 200;
context.font = "24px arial";
context.textAlign = "center";
context.lineJoin = "round"; // to prevent miter spurs on strokeText
//fill smaller canvas with random pixels
for(var x = 0; x < 100; x++){
for(var y = 0; y < 100; y++) {
var rando = function(){return Math.floor(Math.random() * 9)};
var val = rando();
if(x === 0 || y === 0 || x === 99 || y === 99){
context2.fillStyle = "#FF0000";
}else{
context2.fillStyle = "#" + val + val + val;
}
context2.fillRect(x,y,1,1);
}
}
// mouse holds mouse position button state, and if mouse over canvas with overid
var mouse = {
pos : {x : 0, y : 0},
worldPos : {x : 0, y : 0},
posLast : {x : 0, y : 0},
button : false,
overId : "", // id of element mouse is over
dragging : false,
whichWheel : -1, // first wheel event will get the wheel
wheel : 0,
}
// View handles zoom and pan (can also handle rotate but have taken that out as rotate can not be contrained without losing some of the image or seeing some of the background.
const view = (()=>{
const matrix = [1,0,0,1,0,0]; // current view transform
const invMatrix = [1,0,0,1,0,0]; // current inverse view transform
var m = matrix; // alias
var im = invMatrix; // alias
var scale = 1; // current scale
const bounds = {
topLeft : 0,
left : 0,
right : 200,
bottom : 200,
}
var useConstraint = true; // if true then limit pan and zoom to
// keep bounds within the current context
var maxScale = 1;
const workPoint1 = {x :0, y : 0};
const workPoint2 = {x :0, y : 0};
const wp1 = workPoint1; // alias
const wp2 = workPoint2; // alias
var ctx;
const pos = { // current position of origin
x : 0,
y : 0,
}
var dirty = true;
const API = {
canvasDefault () { ctx.setTransform(1,0,0,1,0,0) },
apply(){
if(dirty){ this.update() }
ctx.setTransform(m[0],m[1],m[2],m[3],m[4],m[5]);
},
getScale () { return scale },
getMaxScale () { return maxScale },
matrix, // expose the matrix
invMatrix, // expose the inverse matrix
update(){ // call to update transforms
dirty = false;
m[3] = m[0] = scale;
m[1] = m[2] = 0;
m[4] = pos.x;
m[5] = pos.y;
if(useConstraint){
this.constrain();
}
this.invScale = 1 / scale;
// calculate the inverse transformation
var cross = m[0] * m[3] - m[1] * m[2];
im[0] = m[3] / cross;
im[1] = -m[1] / cross;
im[2] = -m[2] / cross;
im[3] = m[0] / cross;
},
constrain(){
maxScale = Math.min(
ctx.canvas.width / (bounds.right - bounds.left) ,
ctx.canvas.height / (bounds.bottom - bounds.top)
);
if (scale < maxScale) { m[0] = m[3] = scale = maxScale }
wp1.x = bounds.left;
wp1.y = bounds.top;
this.toScreen(wp1,wp2);
if (wp2.x > 0) { m[4] = pos.x -= wp2.x }
if (wp2.y > 0) { m[5] = pos.y -= wp2.y }
wp1.x = bounds.right;
wp1.y = bounds.bottom;
this.toScreen(wp1,wp2);
if (wp2.x < ctx.canvas.width) { m[4] = (pos.x -= wp2.x - ctx.canvas.width) }
if (wp2.y < ctx.canvas.height) { m[5] = (pos.y -= wp2.y - ctx.canvas.height) }
},
toWorld(from,point = {}){ // convert screen to world coords
var xx, yy;
if(dirty){ this.update() }
xx = from.x - m[4];
yy = from.y - m[5];
point.x = xx * im[0] + yy * im[2];
point.y = xx * im[1] + yy * im[3];
return point;
},
toScreen(from,point = {}){ // convert world coords to screen coords
if(dirty){ this.update() }
point.x = from.x * m[0] + from.y * m[2] + m[4];
point.y = from.x * m[1] + from.y * m[3] + m[5];
return point;
},
scaleAt(at, amount){ // at in screen coords
if(dirty){ this.update() }
scale *= amount;
pos.x = at.x - (at.x - pos.x) * amount;
pos.y = at.y - (at.y - pos.y) * amount;
dirty = true;
},
move(x,y){ // move is in screen coords
pos.x += x;
pos.y += y;
dirty = true;
},
setContext(context){
ctx = context;
dirty = true;
},
setBounds(top,left,right,bottom){
bounds.top = top;
bounds.left = left;
bounds.right = right;
bounds.bottom = bottom;
useConstraint = true;
dirty = true;
}
};
return API;
})();
view.setBounds(0,0,canvas2.width,canvas2.height);
view.setContext(context);
//draw the larger canvas
function draw(){
view.canvasDefault(); // se default transform to clear screen
context.imageSmoothingEnabled = false;
context.fillStyle = "white";
context.fillRect(0, 0, width, height);
view.apply(); // set the current view
context.drawImage(canvas2, 0,0);
view.canvasDefault();
if(view.getScale() === view.getMaxScale()){
context.fillStyle = "black";
context.strokeStyle = "white";
context.lineWidth = 2.5;
context.strokeText("Max scale.",context.canvas.width / 2,24);
context.fillText("Max scale.",context.canvas.width / 2,24);
}
requestAnimationFrame(draw);
if(mouse.overId === "canvas"){
canvas.style.cursor = mouse.button ? "none" : "move";
}else{
canvas.style.cursor = "default";
}
}
// add events to document so that mouse is captured when down on canvas
// This allows the mouseup event to be heard no matter where the mouse has
// moved to.
"mousemove,mousedown,mouseup,mousewheel,wheel,DOMMouseScroll".split(",")
.forEach(eventName=>document.addEventListener(eventName,mouseEvent));
function mouseEvent (event){
mouse.overId = event.target.id;
if(event.target.id === "canvas" || mouse.dragging){ // only interested in canvas mouse events including drag event started on the canvas.
mouse.posLast.x = mouse.pos.x;
mouse.posLast.y = mouse.pos.y;
mouse.pos.x = event.clientX - canvas.offsetLeft;
mouse.pos.y = event.clientY - canvas.offsetTop;
view.toWorld(mouse.pos, mouse.worldPos); // gets the world coords (where on canvas 2 the mouse is)
if (event.type === "mousemove"){
if(mouse.button){
view.move(
mouse.pos.x - mouse.posLast.x,
mouse.pos.y - mouse.posLast.y
)
}
} else if (event.type === "mousedown") { mouse.button = true; mouse.dragging = true }
else if (event.type === "mouseup") { mouse.button = false; mouse.dragging = false }
else if(event.type === "mousewheel" && (mouse.whichWheel === 1 || mouse.whichWheel === -1)){
mouse.whichWheel = 1;
mouse.wheel = event.wheelDelta;
}else if(event.type === "wheel" && (mouse.whichWheel === 2 || mouse.whichWheel === -1)){
mouse.whichWheel = 2;
mouse.wheel = -event.deltaY;
}else if(event.type === "DOMMouseScroll" && (mouse.whichWheel === 3 || mouse.whichWheel === -1)){
mouse.whichWheel = 3;
mouse.wheel = -event.detail;
}
if(mouse.wheel !== 0){
event.preventDefault();
view.scaleAt(mouse.pos, Math.exp((mouse.wheel / 120) *zoomIntensity));
mouse.wheel = 0;
}
}
}
div { user-select: none;} /* mouse prevent drag selecting content */
canvas { border:2px solid black;}
<div>
<canvas id="canvas" width="200" height="200"></canvas>
<canvas id="canvas2" width="100" height="100"></canvas>
<p>Mouse wheel to zoom. Mouse click drag to pan.</p>
<p>Zoomed image constrained to canvas</p>
</div>
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