调整矩形HTML5画布(Resize Rectangle HTML5 Canvas)

我有一些功能来绘制canvas元素的矩形。 当元素绘制的，我希望能够通过拖动边角以调整其大小。

 var canvas = document.getElementById('canvas'), ctx = canvas.getContext('2d'), rect = {}, drag = false; function init() { canvas.addEventListener('mousedown', mouseDown, false); canvas.addEventListener('mouseup', mouseUp, false); canvas.addEventListener('mousemove', mouseMove, false); } function mouseDown(e) { rect.startX = e.pageX - this.offsetLeft; rect.startY = e.pageY - this.offsetTop; drag = true; } function mouseUp() { drag = false; } function mouseMove(e) { if (drag) { rect.w = (e.pageX - this.offsetLeft) - rect.startX; rect.h = (e.pageY - this.offsetTop) - rect.startY; ctx.clearRect(0, 0, canvas.width, canvas.height); draw(); } } function draw() { ctx.fillRect(rect.startX, rect.startY, rect.w, rect.h); } init(); 

 <canvas id="canvas" width="500" height="500"></canvas> 

Answer 1:

确保使用某种类型的阈值，以检查是否存在拖延的角落，使用closeEnough变量来保存这个阈值，则通过观察检查边角是否角点和鼠标点之间的差值的绝对值小于阈值。 除此之外，它仅仅是一个很多情况下要经过。 下面是它的一个的jsfiddle

var canvas = document.getElementById('canvas'),
    ctx = canvas.getContext('2d'),
    rect = {},
    drag = false,
    mouseX, 
    mouseY,
    closeEnough = 10,
    dragTL=dragBL=dragTR=dragBR=false;

function init() {
  canvas.addEventListener('mousedown', mouseDown, false);
  canvas.addEventListener('mouseup', mouseUp, false);
  canvas.addEventListener('mousemove', mouseMove, false);
}

function mouseDown(e) {
  mouseX = e.pageX - this.offsetLeft;
  mouseY = e.pageY - this.offsetTop;

  // if there isn't a rect yet
  if(rect.w === undefined){
    rect.startX = mouseY;
    rect.startY = mouseX;
    dragBR = true;
  }

  // if there is, check which corner
  //   (if any) was clicked
  //
  // 4 cases:
  // 1. top left
  else if( checkCloseEnough(mouseX, rect.startX) && checkCloseEnough(mouseY, rect.startY) ){
    dragTL = true;
  }
  // 2. top right
  else if( checkCloseEnough(mouseX, rect.startX+rect.w) && checkCloseEnough(mouseY, rect.startY) ){
    dragTR = true;

  }
  // 3. bottom left
  else if( checkCloseEnough(mouseX, rect.startX) && checkCloseEnough(mouseY, rect.startY+rect.h) ){
    dragBL = true;

  }
  // 4. bottom right
  else if( checkCloseEnough(mouseX, rect.startX+rect.w) && checkCloseEnough(mouseY, rect.startY+rect.h) ){
    dragBR = true;

  }
  // (5.) none of them
  else {
    // handle not resizing
  }

  ctx.clearRect(0,0,canvas.width,canvas.height);
  draw();

}

function checkCloseEnough(p1, p2){
  return Math.abs(p1-p2)<closeEnough;
}
function mouseUp() {
  dragTL = dragTR = dragBL = dragBR = false;
}

function mouseMove(e) {
  mouseX = e.pageX - this.offsetLeft;
  mouseY = e.pageY - this.offsetTop;
  if(dragTL){
    rect.w += rect.startX-mouseX;
    rect.h += rect.startY-mouseY;
    rect.startX = mouseX;
    rect.startY = mouseY;
  } else if(dragTR) {
    rect.w = Math.abs(rect.startX-mouseX);
    rect.h += rect.startY-mouseY;
    rect.startY = mouseY;
  } else if(dragBL) {
    rect.w += rect.startX-mouseX;
    rect.h = Math.abs(rect.startY-mouseY);
    rect.startX = mouseX;  
  } else if(dragBR) {
    rect.w = Math.abs(rect.startX-mouseX);
    rect.h = Math.abs(rect.startY-mouseY);
  }
    ctx.clearRect(0,0,canvas.width,canvas.height);
    draw();
}

function draw() {
  ctx.fillRect(rect.startX, rect.startY, rect.w, rect.h);
}

init();

Answer 2:

做一个处理系统：当鼠标移动，让距离各个角落拿到第一个就是近光标，然后将其保存，并根据其调整您的矩形。

下面是一个说明的jsfiddle它： http://jsfiddle.net/BaliBalo/9HXMG/

function getHandle(mouse) {
    if (dist(mouse, point(rect.x, rect.y)) <= handlesSize) return 'topleft';
    if (dist(mouse, point(rect.x + rect.w, rect.y)) <= handlesSize) return 'topright';
    if (dist(mouse, point(rect.x, rect.y + rect.h)) <= handlesSize) return 'bottomleft';
    if (dist(mouse, point(rect.x + rect.w, rect.y + rect.h)) <= handlesSize) return 'bottomright';
    if (dist(mouse, point(rect.x + rect.w / 2, rect.y)) <= handlesSize) return 'top';
    if (dist(mouse, point(rect.x, rect.y + rect.h / 2)) <= handlesSize) return 'left';
    if (dist(mouse, point(rect.x + rect.w / 2, rect.y + rect.h)) <= handlesSize) return 'bottom';
    if (dist(mouse, point(rect.x + rect.w, rect.y + rect.h / 2)) <= handlesSize) return 'right';
    return false;
}

文章来源: Resize Rectangle HTML5 Canvas