In diesem Artikel wird hauptsächlich die Methode zur Verwendung von JavaScript + Canvas zum Zuschneiden von Bildern vorgestellt.
Canvas ist ein Tag, mit dem wir Skriptzeichnungen verwenden können von Eigenschaften und Methoden. Damit können wir Grafikzeichnungen, Bildverarbeitung und sogar einfache Animationen und Spiele produzieren.
Das Canvas-Tag hat nur zwei Attribute: Breite und Höhe, die zum Festlegen der Breite und Höhe der Leinwand verwendet werden. Wenn sie nicht über Tag-Attribute oder Skripte festgelegt werden, ist der Standardwert 300*150;
Okay Okay, hier ist zuerst die Einführung in Canvas. Schauen wir uns den Code zum Zuschneiden von Bildern mit Javascript in Kombination mit Canvas an:
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 = $("<canvas></canvas>")[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;
}Das Obige ist der gesamte Inhalt dieses Artikels Wird für das Lernen aller hilfreich sein. Weitere Informationen finden Sie auf der chinesischen PHP-Website.
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