Question

所以我目前正在开发一个迷你项目，需要帮助我使用一些代码来放大和缩小HTML画布。

我想添加限制：

放大和缩小的距离（对象的最小和最大尺寸）。
您可以在屏幕上平移多远。（屏幕的初始边缘作为限制）

这是我正在使用的代码

var canvas = document.querySelector('canvas');  // selecting the canvas element in html file, the assigning to a variable

canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

var ctx = canvas.getContext('2d');

window.onload = function(){		
    
		    
            trackTransforms(ctx);
            
    function Object (x, y, radius, color) {
        this.x = x;
        this.y = y;
        this.radius = radius;
        this.color = color;
    
        this.draw = function () {
            ctx.beginPath();
            ctx.arc(this.x, this.y, this.radius, 0, Math.PI*2, false);
            ctx.fillStyle = this.color;
            ctx.fill();
            ctx.closePath();
        };
    }
    
    function init(x, systemRadi, systemColor, scaleVal){
        var y = canvas.height/2
        var planets = [];
        for (var i= 0; i< systemRadi.length; i++){
            planets.push(new Object(x[i], y, systemRadi[i]*scaleVal, systemColor[i]))
        }
        animate(planets);
    
    }    
    function animate(planets){
            planets.forEach(function(Object) {
                Object.draw();
            }, this);
        }
    
    
    
    function main(){
        var scaleVal = 100;
        var r = [0.6957,0.0049,0.0121,0.0128,0.0068,0.143,0.1205,0.0511,0.0495,0.0028];
        var x =[-r[0]*scaleVal/4,11.6 + r[0]*scaleVal,21.6 + r[0]*scaleVal,29.9 + r[0]*scaleVal,45.6 + r[0]*scaleVal,155.8 + r[0]*scaleVal,286 + r[0]*scaleVal,574 + r[0]*scaleVal,899 + r[0]*scaleVal,1300 + r[0]*scaleVal];
        
        var col = ['rgb(242, 181, 50)','rgb(40, 8, 8)', 'rgb(124, 175, 35)','rgb(32, 32, 155)', 'rgb(196, 70, 39)', 'rgb(219, 125, 43)','rgb(219, 182, 37)', 'rgb(37, 140, 219)', 'rgb(37, 185, 219)', 'rgb(5, 10, 20)']
        init(x, r, col, scaleVal);
    
    
    }

    
		  
    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.save();
          ctx.setTransform(1,0,0,1,0,0);
          ctx.clearRect(0,0,canvas.width,canvas.height);
          ctx.restore();

          main();    // create image

        }
        redraw(); // redraw the image upon transformation

      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);
          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);
            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);
	};

	
	// 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());
      }
    }

<!DOCTYPE html>
<html>
    <head>
        <style type="text/css">
            canvas {
                border: thin solid black;
            }
            body{
                margin: 0;
            }
        </style>
    </head>
    <body>
        <canvas></canvas>
        <script src="tester.js"></script>
    </body>
</html>

我是javascript的新手，所以请以任何可能的方式提供帮助。如果可能的话，请解释一下你在做什么以及为什么我要更好地理解代码，而不仅仅是让一些有用的东西。

非常感谢。

Answer 1

scale(x, y)方法中的zoom函数调用是处理缩放的函数。 scale函数有两个参数x和y，x表示上下文应沿x轴缩放多少，y表示其对应的y。

因此，您可以做的是维护一个存储当前缩放级别的全局变量，并在每次触发缩放操作时对其进行检查。

您可以扩展相同的想法来限制平移（由mousedown和mousemove方法处理）。保持跟踪当前位置的全局值，并在每次触发平移动作时根据比例和边界对其进行检查。

HTML Canvas：使用限制进行缩放和平移

1 个答案: