YangZhouDaYunHeDaDu/public/static/lib/canvas2Image.js

/*
 * Canvas2Image v0.1
 * Copyright (c) 2008 Jacob Seidelin, cupboy@gmail.com
 * MIT License [http://www.opensource.org/licenses/mit-license.php]
 */

var Canvas2Image = (function() {
    // check if we have canvas support
    var oCanvas = document.createElement("canvas"),
        sc = String.fromCharCode,
        strDownloadMime = "image/octet-stream",
        bReplaceDownloadMime = false;

    // no canvas, bail out.
    if (!oCanvas.getContext) {
        return {
            saveAsBMP : function(){},
            saveAsPNG : function(){},
            saveAsJPEG : function(){}
        }
    }

    var bHasImageData = !!(oCanvas.getContext("2d").getImageData),
        bHasDataURL = !!(oCanvas.toDataURL),
        bHasBase64 = !!(window.btoa);

    // ok, we're good
    var readCanvasData = function(oCanvas) {
        var iWidth = parseInt(oCanvas.width),
            iHeight = parseInt(oCanvas.height);
        return oCanvas.getContext("2d").getImageData(0,0,iWidth,iHeight);
    }

    // base64 encodes either a string or an array of charcodes
    var encodeData = function(data) {
        var i, aData, strData = "";

        if (typeof data == "string") {
            strData = data;
        } else {
            aData = data;
            for (i = 0; i < aData.length; i++) {
                strData += sc(aData[i]);
            }
        }
        return btoa(strData);
    }

    // creates a base64 encoded string containing BMP data takes an imagedata object as argument
    var createBMP = function(oData) {
        var strHeader = '',
            iWidth = oData.width,
            iHeight = oData.height;

        strHeader += 'BM';

        var iFileSize = iWidth*iHeight*4 + 54; // total header size = 54 bytes
        strHeader += sc(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
        strHeader += sc(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
        strHeader += sc(iFileSize % 256); iFileSize = Math.floor(iFileSize / 256);
        strHeader += sc(iFileSize % 256);

        strHeader += sc(0, 0, 0, 0, 54, 0, 0, 0); // data offset
        strHeader += sc(40, 0, 0, 0); // info header size

        var iImageWidth = iWidth;
        strHeader += sc(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
        strHeader += sc(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
        strHeader += sc(iImageWidth % 256); iImageWidth = Math.floor(iImageWidth / 256);
        strHeader += sc(iImageWidth % 256);

        var iImageHeight = iHeight;
        strHeader += sc(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
        strHeader += sc(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
        strHeader += sc(iImageHeight % 256); iImageHeight = Math.floor(iImageHeight / 256);
        strHeader += sc(iImageHeight % 256);

        strHeader += sc(1, 0, 32, 0); // num of planes & num of bits per pixel
        strHeader += sc(0, 0, 0, 0); // compression = none

        var iDataSize = iWidth*iHeight*4;
        strHeader += sc(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
        strHeader += sc(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
        strHeader += sc(iDataSize % 256); iDataSize = Math.floor(iDataSize / 256);
        strHeader += sc(iDataSize % 256);

        strHeader += sc(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0); // these bytes are not used

        var aImgData = oData.data,
            strPixelData = "",
            c, x, y = iHeight,
            iOffsetX, iOffsetY, strPixelRow;

        do {
            iOffsetY = iWidth*(y-1)*4;
            strPixelRow = "";
            for (x = 0; x < iWidth; x++) {
                iOffsetX = 4*x;
                strPixelRow += sc(
                    aImgData[iOffsetY + iOffsetX + 2], // B
                    aImgData[iOffsetY + iOffsetX + 1], // G
                    aImgData[iOffsetY + iOffsetX], // R
                    aImgData[iOffsetY + iOffsetX + 3] // A
                );
            }
            strPixelData += strPixelRow;
        } while (--y);

        return encodeData(strHeader + strPixelData);
    }

    // sends the generated file to the client
    var saveFile = function(strData) {
        if (!window.open(strData)) {
            document.location.href = strData;
        }
    }

    var makeDataURI = function(strData, strMime) {
        return "data:" + strMime + ";base64," + strData;
    }

    // generates a <img> object containing the imagedata
    var makeImageObject = function(strSource) {
        var oImgElement = document.createElement("img");
        oImgElement.src = strSource;
        return oImgElement;
    }

    var scaleCanvas = function(oCanvas, iWidth, iHeight) {
        if (iWidth && iHeight) {
            var oSaveCanvas = document.createElement("canvas");

            oSaveCanvas.width = iWidth;
            oSaveCanvas.height = iHeight;
            oSaveCanvas.style.width = iWidth+"px";
            oSaveCanvas.style.height = iHeight+"px";

            var oSaveCtx = oSaveCanvas.getContext("2d");

            oSaveCtx.drawImage(oCanvas, 0, 0, oCanvas.width, oCanvas.height, 0, 0, iWidth, iWidth);

            return oSaveCanvas;
        }
        return oCanvas;
    }

    return {
        saveAsPNG : function(oCanvas, bReturnImg, iWidth, iHeight) {
            if (!bHasDataURL) return false;
            var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight),
                strMime = "image/png",
                strData = oScaledCanvas.toDataURL(strMime);

            if (bReturnImg) {
                return makeImageObject(strData);
            } else {
                saveFile(bReplaceDownloadMime ? strData.replace(strMime, strDownloadMime) : strData);
            }
            return true;
        },

        saveAsJPEG : function(oCanvas, bReturnImg, iWidth, iHeight) {
            if (!bHasDaaURL) return false;

            var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight),
                strMime = "image/jpeg",
                strData = oScaledCanvas.toDataURL(strMime);

            // check if browser actually supports jpeg by looking for the mime type in the data uri. if not, return false
            if (strData.indexOf(strMime) != 5) return false;

            if (bReturnImg) {
                return makeImageObject(strData);
            } else {
                saveFile(bReplaceDownloadMime ? strData.replace(strMime, strDownloadMime) : strData);
            }
            return true;
        },

        saveAsBMP : function(oCanvas, bReturnImg, iWidth, iHeight) {
            if (!(bHasDataURL && bHasImageData && bHasBase64)) return false;

            var oScaledCanvas = scaleCanvas(oCanvas, iWidth, iHeight),
                strMime = "image/bmp",
                oData = readCanvasData(oScaledCanvas),
                strImgData = createBMP(oData);

            if (bReturnImg) {
                return makeImageObject(makeDataURI(strImgData, strMime));
            } else {
                saveFile(makeDataURI(strImgData, strMime));
            }
            return true;
        }
    };
})();