如何使用JavaScript和canvas实现图片裁剪的功能
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canvas是一个可以让我们使用脚本绘图的标签,它提供了一系列完整的属性和方法。我们可以借此来实现图形绘制,图像处理甚至实现简单的动画和游戏制作。
canvas标签只有两个属性:width和height,用来设定画布的宽和高,如果没有通过标签属性或者脚本来设置,默认为300*150;
好了,canvas的介绍就先到这里,下面我们来看看javascript结合canvas实现图片的裁剪代码:
var selectObj = null; function ImageCrop(canvasId, imageSource, x, y, width, height) { var canvas = $("#" + canvasId); if (canvas.length == 0 && imageSource) { return; } function canvasMouseDown(e) { StopSelect(e); canvas.css("cursor", "default"); } function canvasMouseMove(e) { var canvasOffset = canvas.offset(); var pageX = e.pageX || event.targetTouches[0].pageX; var pageY = e.pageY || event.targetTouches[0].pageY; iMouseX = Math.floor(pageX - canvasOffset.left); iMouseY = Math.floor(pageY - canvasOffset.top); canvas.css("cursor", "default"); if (selectObj.bDragAll) { canvas.css("cursor", "move"); canvas.data("drag", true); var cx = iMouseX - selectObj.px; cx = cx < 0 ? 0 : cx; mx = ctx.canvas.width - selectObj.w; cx = cx > mx ? mx : cx; selectObj.x = cx; var cy = iMouseY - selectObj.py; cy = cy < 0 ? 0 : cy; my = ctx.canvas.height - selectObj.h; cy = cy > my ? my : cy; selectObj.y = cy; } for (var i = 0; i < 4; i++) { selectObj.bHow[i] = false; selectObj.iCSize[i] = selectObj.csize; } // hovering over resize cubes if (iMouseX > selectObj.x - selectObj.csizeh && iMouseX < selectObj.x + selectObj.csizeh && iMouseY > selectObj.y - selectObj.csizeh && iMouseY < selectObj.y + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[0] = true; selectObj.iCSize[0] = selectObj.csizeh; } if (iMouseX > selectObj.x + selectObj.w - selectObj.csizeh && iMouseX < selectObj.x + selectObj.w + selectObj.csizeh && iMouseY > selectObj.y - selectObj.csizeh && iMouseY < selectObj.y + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[1] = true; selectObj.iCSize[1] = selectObj.csizeh; } if (iMouseX > selectObj.x + selectObj.w - selectObj.csizeh && iMouseX < selectObj.x + selectObj.w + selectObj.csizeh && iMouseY > selectObj.y + selectObj.h - selectObj.csizeh && iMouseY < selectObj.y + selectObj.h + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[2] = true; selectObj.iCSize[2] = selectObj.csizeh; } if (iMouseX > selectObj.x - selectObj.csizeh && iMouseX < selectObj.x + selectObj.csizeh && iMouseY > selectObj.y + selectObj.h - selectObj.csizeh && iMouseY < selectObj.y + selectObj.h + selectObj.csizeh) { canvas.css("cursor", "pointer"); selectObj.bHow[3] = true; selectObj.iCSize[3] = selectObj.csizeh; } if (iMouseX > selectObj.x && iMouseX < selectObj.x + selectObj.w && iMouseY > selectObj.y && iMouseY < selectObj.y + selectObj.h) { canvas.css("cursor", "move"); } // in case of dragging of resize cubes var iFW, iFH, iFX, iFY, mx, my; if (selectObj.bDrag[0]) { iFX = iMouseX - selectObj.px; iFY = iMouseY - selectObj.py; iFW = selectObj.w + selectObj.x - iFX; iFH = selectObj.h + selectObj.y - iFY; canvas.data("drag", true); } if (selectObj.bDrag[1]) { iFX = selectObj.x; iFY = iMouseY - selectObj.py; iFW = iMouseX - selectObj.px - iFX; iFH = selectObj.h + selectObj.y - iFY; canvas.data("drag", true); } if (selectObj.bDrag[2]) { iFX = selectObj.x; iFY = selectObj.y; iFW = iMouseX - selectObj.px - iFX; iFH = iMouseY - selectObj.py - iFY; canvas.data("drag", true); } if (selectObj.bDrag[3]) { iFX = iMouseX - selectObj.px; iFY = selectObj.y; iFW = selectObj.w + selectObj.x - iFX; iFH = iMouseY - selectObj.py - iFY; canvas.data("drag", true); } if (iFW > selectObj.csizeh * 2 && iFH > selectObj.csizeh * 2) { selectObj.w = iFW; selectObj.h = iFH; selectObj.x = iFX; selectObj.y = iFY; } drawScene(); } function canvasMouseOut() { $(canvas).trigger("mouseup"); } function canvasMouseUp() { selectObj.bDragAll = false; for (var i = 0; i < 4; i++) { selectObj.bDrag[i] = false; } canvas.css("cursor", "default"); canvas.data("select", { x: selectObj.x, y: selectObj.y, w: selectObj.w, h: selectObj.h }); selectObj.px = 0; selectObj.py = 0; } function Selection(x, y, w, h) { this.x = x; // initial positions this.y = y; this.w = w; // and size this.h = h; this.px = x; // extra variables to dragging calculations this.py = y; this.csize = 4; // resize cubes size this.csizeh = 6; // resize cubes size (on hover) this.bHow = [false, false, false, false]; // hover statuses this.iCSize = [this.csize, this.csize, this.csize, this.csize]; // resize cubes sizes this.bDrag = [false, false, false, false]; // drag statuses this.bDragAll = false; // drag whole selection } Selection.prototype.draw = function () { ctx.strokeStyle = '#666'; ctx.lineWidth = 2; ctx.strokeRect(this.x, this.y, this.w, this.h); // draw part of original image if (this.w > 0 && this.h > 0) { ctx.drawImage(image, this.x, this.y, this.w, this.h, this.x, this.y, this.w, this.h); } // draw resize cubes ctx.fillStyle = '#999'; ctx.fillRect(this.x - this.iCSize[0], this.y - this.iCSize[0], this.iCSize[0] * 2, this.iCSize[0] * 2); ctx.fillRect(this.x + this.w - this.iCSize[1], this.y - this.iCSize[1], this.iCSize[1] * 2, this.iCSize[1] * 2); ctx.fillRect(this.x + this.w - this.iCSize[2], this.y + this.h - this.iCSize[2], this.iCSize[2] * 2, this.iCSize[2] * 2); ctx.fillRect(this.x - this.iCSize[3], this.y + this.h - this.iCSize[3], this.iCSize[3] * 2, this.iCSize[3] * 2); }; var drawScene = function () { ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height); // clear canvas // draw source image ctx.drawImage(image, 0, 0, ctx.canvas.width, ctx.canvas.height); // and make it darker ctx.fillStyle = 'rgba(0, 0, 0, 0.5)'; ctx.fillRect(0, 0, ctx.canvas.width, ctx.canvas.height); // draw selection selectObj.draw(); canvas.mousedown(canvasMouseDown); canvas.on("touchstart", canvasMouseDown); }; var createSelection = function (x, y, width, height) { var content = $("#imagePreview"); x = x || Math.ceil((content.width() - width) / 2); y = y || Math.ceil((content.height() - height) / 2); return new Selection(x, y, width, height); }; var ctx = canvas[0].getContext("2d"); var iMouseX = 1; var iMouseY = 1; var image = new Image(); image.onload = function () { selectObj = createSelection(x, y, width, height); canvas.data("select", { x: selectObj.x, y: selectObj.y, w: selectObj.w, h: selectObj.h }); drawScene(); }; image.src = imageSource; canvas.mousemove(canvasMouseMove); canvas.on("touchmove", canvasMouseMove); var StopSelect = function (e) { var canvasOffset = $(canvas).offset(); var pageX = e.pageX || event.targetTouches[0].pageX; var pageY = e.pageY || event.targetTouches[0].pageY; iMouseX = Math.floor(pageX - canvasOffset.left); iMouseY = Math.floor(pageY - canvasOffset.top); selectObj.px = iMouseX - selectObj.x; selectObj.py = iMouseY - selectObj.y; if (selectObj.bHow[0]) { selectObj.px = iMouseX - selectObj.x; selectObj.py = iMouseY - selectObj.y; } if (selectObj.bHow[1]) { selectObj.px = iMouseX - selectObj.x - selectObj.w; selectObj.py = iMouseY - selectObj.y; } if (selectObj.bHow[2]) { selectObj.px = iMouseX - selectObj.x - selectObj.w; selectObj.py = iMouseY - selectObj.y - selectObj.h; } if (selectObj.bHow[3]) { selectObj.px = iMouseX - selectObj.x; selectObj.py = iMouseY - selectObj.y - selectObj.h; } if (iMouseX > selectObj.x + selectObj.csizeh && iMouseX < selectObj.x + selectObj.w - selectObj.csizeh && iMouseY > selectObj.y + selectObj.csizeh && iMouseY < selectObj.y + selectObj.h - selectObj.csizeh) { selectObj.bDragAll = true; } for (var i = 0; i < 4; i++) { if (selectObj.bHow[i]) { selectObj.bDrag[i] = true; } } }; canvas.mouseout(canvasMouseOut); canvas.mouseup(canvasMouseUp); canvas.on("touchend", canvasMouseUp); this.getImageData = function (previewID) { var tmpCanvas = $("")[0]; var tmpCtx = tmpCanvas.getContext("2d"); if (tmpCanvas && selectObj) { tmpCanvas.width = selectObj.w; tmpCanvas.height = selectObj.h; tmpCtx.drawImage(image, selectObj.x, selectObj.y, selectObj.w, selectObj.h, 0, 0, selectObj.w, selectObj.h); if (document.getElementById(previewID)) { document.getElementById(previewID).src = tmpCanvas.toDataURL(); document.getElementById(previewID).style.border = "1px solid #ccc"; } return tmpCanvas.toDataURL(); } }; } function autoResizeImage(maxWidth, maxHeight, objImg) { var img = new Image(); img.src = objImg.src; var hRatio; var wRatio; var ratio = 1; var w = objImg.width; var h = objImg.height; wRatio = maxWidth / w; hRatio = maxHeight / h; if (w < maxWidth && h < maxHeight) { return; } if (maxWidth == 0 && maxHeight == 0) { ratio = 1; } else if (maxWidth == 0) { if (hRatio < 1) { ratio = hRatio; } } else if (maxHeight == 0) { if (wRatio < 1) { ratio = wRatio; } } else if (wRatio < 1 || hRatio < 1) { ratio = (wRatio <= hRatio ? wRatio : hRatio); } else { ratio = (wRatio <= hRatio ? wRatio : hRatio) - Math.floor(wRatio <= hRatio ? wRatio : hRatio); } if (ratio < 1) { if (ratio < 0.5 && w < maxWidth && h < maxHeight) { ratio = 1 - ratio; } w = w * ratio; h = h * ratio; } objImg.height = h; objImg.width = w; }
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