Qt加载大图片（图片较大无法正常加载 显示空白处理方法）

最近在项目中实现壁纸预览功能时，遇到了图片无法正常加载的问题。开始策略是在重绘事件中直接加载硬盘中的图片文件，代码如下:

void YourClass::paintEvent(QPaintEvent* event){QPainter p(this);p.drawPixmap(0, 0, width(), height(), QPixmap("E:/c++proj/testBlog/StockSnap_3C5NLBSRKD.jpg").scaled(width(), height(), Qt::KeepAspectRatio));}

当图片较大的时候,主机性能较差时，界面显示白屏，无法正常加载图片。效果如下：

之后变选择使用imagereader的方法读取图片：代码如下：

void YourClass::paintEvent(QPaintEvent* event){QPainter p(this);QImageReader reader;QImage image;reader.setDecideFormatFromContent(true);reader.setScaledSize(QSize(width(), height()));reader.setFileName("E:/c++proj/testBlog/Image/StockSnap_3C5NLBSRKD.jpg");if (reader.canRead()){if (!reader.read(&image)){QImageReader::ImageReaderError error = reader.error();QString strError = reader.errorString();printf("last error:%s\n", strError.toStdString().c_str());return;}}p.drawPixmap(0, 0, width(), height(), QPixmap::fromImage(image)/*.scaled(width(), height(), Qt::KeepAspectRatio)*/);}

此时可正常显示：

但遇到一个100M的BMP图片无法加载的问题，查阅资料得知加载时较大的图片会因内存不足无法加载，显示一片空白，此时可通过分段读取的方法解决。

具体代码如下：

QBmpLoader.h

#pragma once#include <QtGui/QImageIOHandler>struct BMP_FILEHDR { // BMP file headerchar bfType[2];// "BM"qint32 bfSize; // size of fileqint16 bfReserved1;qint16 bfReserved2;qint32 bfOffBits; // pointer to the pixmap bits};struct BMP_INFOHDR { // BMP information headerqint32 biSize; // size of this structqint32 biWidth; // pixmap widthqint32 biHeight;// pixmap heightqint16 biPlanes;// should be 1qint16 biBitCount; // number of bits per pixelqint32 biCompression;// compression methodqint32 biSizeImage; // size of imageqint32 biXPelsPerMeter; // horizontal resolutionqint32 biYPelsPerMeter; // vertical resolutionqint32 biClrUsed; // number of colors usedqint32 biClrImportant; // number of important colors};namespace setting{class QBmpLoader{public:enum State {Ready,ReadHeader,Error};QIODevice* device();void setDevice(QIODevice *device);QBmpLoader();bool setImagePath(QString imagePath);bool read(QImage *image);bool read(QImage *image, const QRect& rc);bool read(QImage *image, const QRect& range, double dScalX, double dScalY);bool isOk() { return state != Error; }BMP_FILEHDR fileHeader;BMP_INFOHDR infoHeader;private:bool readHeader();int startpos;QString imagePath;State state;QIODevice *m_device;};}

QBmpLoader.cpp

#include "QBmploader.h"#include <qimage.h>#include <qvariant.h>#include <qvector.h>#include <QFile>#include <QDebug>#include <qmath.h>static void swapPixel01(QImage *image) // 1-bpp: swap 0 and 1 pixels{int i;if (image->depth() == 1 && image->colorCount() == 2) {register uint *p = (uint *)image->bits();int nbytes = image->byteCount();for (i = 0; i<nbytes / 4; i++) {*p = ~*p;p++;}uchar *p2 = (uchar *)p;for (i = 0; i<(nbytes & 3); i++) {*p2 = ~*p2;p2++;}QRgb t = image->color(0);// swap color 0 and 1image->setColor(0, image->color(1));image->setColor(1, t);}}/*QImageIO::defineIOHandler("BMP", "^BM", 0,read_bmp_image, write_bmp_image);*//*****************************************************************************BMP (DIB) image read/write functions*****************************************************************************/const int BMP_FILEHDR_SIZE = 14;// size of BMP_FILEHDR datastatic QDataStream &operator >> (QDataStream &s, BMP_FILEHDR &bf){ // read file headers.readRawData(bf.bfType, 2);s >> bf.bfSize >> bf.bfReserved1 >> bf.bfReserved2 >> bf.bfOffBits;return s;}static QDataStream &operator<<(QDataStream &s, const BMP_FILEHDR &bf){ // write file headers.writeRawData(bf.bfType, 2);s << bf.bfSize << bf.bfReserved1 << bf.bfReserved2 << bf.bfOffBits;return s;}const int BMP_OLD = 12; // old Windows/OS2 BMP sizeconst int BMP_WIN = 40; // Windows BMP v3 sizeconst int BMP_OS2 = 64; // new OS/2 BMP sizeconst int BMP_WIN4 = 108; // Windows BMP v4 sizeconst int BMP_WIN5 = 124; // Windows BMP v5 sizeconst int BMP_RGB = 0; // no compressionconst int BMP_RLE8 = 1; // run-length encoded, 8 bitsconst int BMP_RLE4 = 2; // run-length encoded, 4 bitsconst int BMP_BITFIELDS = 3; // RGB values encoded in data as bit-fieldsstatic QDataStream &operator >> (QDataStream &s, BMP_INFOHDR &bi){s >> bi.biSize;if (bi.biSize == BMP_WIN || bi.biSize == BMP_OS2 || bi.biSize == BMP_WIN4 || bi.biSize == BMP_WIN5) {s >> bi.biWidth >> bi.biHeight >> bi.biPlanes >> bi.biBitCount;s >> bi.biCompression >> bi.biSizeImage;s >> bi.biXPelsPerMeter >> bi.biYPelsPerMeter;s >> bi.biClrUsed >> bi.biClrImportant;}else {// probably old Windows formatqint16 w, h;s >> w >> h >> bi.biPlanes >> bi.biBitCount;bi.biWidth = w;bi.biHeight = h;bi.biCompression = BMP_RGB;// no compressionbi.biSizeImage = 0;bi.biXPelsPerMeter = bi.biYPelsPerMeter = 0;bi.biClrUsed = bi.biClrImportant = 0;}return s;}static QDataStream &operator<<(QDataStream &s, const BMP_INFOHDR &bi){s << bi.biSize;s << bi.biWidth << bi.biHeight;s << bi.biPlanes;s << bi.biBitCount;s << bi.biCompression;s << bi.biSizeImage;s << bi.biXPelsPerMeter << bi.biYPelsPerMeter;s << bi.biClrUsed << bi.biClrImportant;return s;}static int calc_shift(int mask){int result = 0;while (mask && !(mask & 1)) {result++;mask >>= 1;}return result;}static bool read_dib_fileheader(QDataStream &s, BMP_FILEHDR &bf){// read BMP file headers >> bf;if (s.status() != QDataStream::Ok)return false;// check headerif (qstrncmp(bf.bfType, "BM", 2) != 0)return false;return true;}static bool read_dib_infoheader(QDataStream &s, BMP_INFOHDR &bi){s >> bi;// read BMP info headerif (s.status() != QDataStream::Ok)return false;int nbits = bi.biBitCount;int comp = bi.biCompression;if (!(nbits == 1 || nbits == 4 || nbits == 8 || nbits == 16 || nbits == 24 || nbits == 32) ||bi.biPlanes != 1 || comp > BMP_BITFIELDS)return false;// weird BMP imageif (!(comp == BMP_RGB || (nbits == 4 && comp == BMP_RLE4) ||(nbits == 8 && comp == BMP_RLE8) || ((nbits == 16 || nbits == 32) && comp == BMP_BITFIELDS)))return false; // weird compression typereturn true;}static bool read_dib_body(QDataStream &s, const BMP_INFOHDR &bi, int offset, int startpos, QImage &image){QIODevice* d = s.device();if (d->atEnd()) // end of stream/filereturn false;#if 0qDebug("offset...........%d", offset);qDebug("startpos.........%d", startpos);qDebug("biSize...........%d", bi.biSize);qDebug("biWidth..........%d", bi.biWidth);qDebug("biHeight.........%d", bi.biHeight);qDebug("biPlanes.........%d", bi.biPlanes);qDebug("biBitCount.......%d", bi.biBitCount);qDebug("biCompression....%d", bi.biCompression);qDebug("biSizeImage......%d", bi.biSizeImage);qDebug("biXPelsPerMeter..%d", bi.biXPelsPerMeter);qDebug("biYPelsPerMeter..%d", bi.biYPelsPerMeter);qDebug("biClrUsed........%d", bi.biClrUsed);qDebug("biClrImportant...%d", bi.biClrImportant);#endifint w = bi.biWidth, h = bi.biHeight, nbits = bi.biBitCount;int t = bi.biSize, comp = bi.biCompression;int red_mask = 0;int green_mask = 0;int blue_mask = 0;int red_shift = 0;int green_shift = 0;int blue_shift = 0;int red_scale = 0;int green_scale = 0;int blue_scale = 0;int ncols = 0;int depth = 0;QImage::Format format;switch (nbits) {case 32:case 24:case 16:depth = 32;format = QImage::Format_RGB32;break;case 8:case 4:depth = 8;format = QImage::Format_Indexed8;break;default:depth = 1;format = QImage::Format_Mono;}if (bi.biHeight < 0)h = -h; // support images with negative heightif (image.size() != QSize(w, h) || image.format() != format) {image = QImage(w, h, format);if (image.isNull()) // could not create imagereturn false;}if (depth != 32) {ncols = bi.biClrUsed ? bi.biClrUsed : 1 << nbits;if (ncols > 256) // sanity check - don't run out of mem if color table is brokenreturn false;image.setColorCount(ncols);}image.setDotsPerMeterX(bi.biXPelsPerMeter);image.setDotsPerMeterY(bi.biYPelsPerMeter);if (!d->isSequential())d->seek(startpos + BMP_FILEHDR_SIZE + (bi.biSize >= BMP_WIN4 ? BMP_WIN : bi.biSize)); // goto start of colormapif (bi.biSize >= BMP_WIN4 || (comp == BMP_BITFIELDS && (nbits == 16 || nbits == 32))) {if (d->read((char *)&red_mask, sizeof(red_mask)) != sizeof(red_mask))return false;if (d->read((char *)&green_mask, sizeof(green_mask)) != sizeof(green_mask))return false;if (d->read((char *)&blue_mask, sizeof(blue_mask)) != sizeof(blue_mask))return false;// Read BMP v4+ headerif (bi.biSize >= BMP_WIN4) {int alpha_mask = 0;int CSType = 0;int gamma_red = 0;int gamma_green = 0;int gamma_blue = 0;int endpoints[9];if (d->read((char *)&alpha_mask, sizeof(alpha_mask)) != sizeof(alpha_mask))return false;if (d->read((char *)&CSType, sizeof(CSType)) != sizeof(CSType))return false;if (d->read((char *)&endpoints, sizeof(endpoints)) != sizeof(endpoints))return false;if (d->read((char *)&gamma_red, sizeof(gamma_red)) != sizeof(gamma_red))return false;if (d->read((char *)&gamma_green, sizeof(gamma_green)) != sizeof(gamma_green))return false;if (d->read((char *)&gamma_blue, sizeof(gamma_blue)) != sizeof(gamma_blue))return false;if (bi.biSize == BMP_WIN5) {qint32 intent = 0;qint32 profileData = 0;qint32 profileSize = 0;qint32 reserved = 0;if (d->read((char *)&intent, sizeof(intent)) != sizeof(intent))return false;if (d->read((char *)&profileData, sizeof(profileData)) != sizeof(profileData))return false;if (d->read((char *)&profileSize, sizeof(profileSize)) != sizeof(profileSize))return false;if (d->read((char *)&reserved, sizeof(reserved)) != sizeof(reserved) || reserved != 0)return false;}}}if (ncols > 0) { // read color tableuchar rgb[4];int rgb_len = t == BMP_OLD ? 3 : 4;for (int i = 0; i<ncols; i++) {if (d->read((char *)rgb, rgb_len) != rgb_len)return false;image.setColor(i, qRgb(rgb[2], rgb[1], rgb[0]));if (d->atEnd()) // truncated filereturn false;}}else if (comp == BMP_BITFIELDS && (nbits == 16 || nbits == 32)) {red_shift = calc_shift(red_mask);red_scale = 256 / ((red_mask >> red_shift) + 1);green_shift = calc_shift(green_mask);green_scale = 256 / ((green_mask >> green_shift) + 1);blue_shift = calc_shift(blue_mask);blue_scale = 256 / ((blue_mask >> blue_shift) + 1);}else if (comp == BMP_RGB && (nbits == 24 || nbits == 32)) {blue_mask = 0x000000ff;green_mask = 0x0000ff00;red_mask = 0x00ff0000;blue_shift = 0;green_shift = 8;red_shift = 16;blue_scale = green_scale = red_scale = 1;}else if (comp == BMP_RGB && nbits == 16) {blue_mask = 0x001f;green_mask = 0x03e0;red_mask = 0x7c00;blue_shift = 0;green_shift = 2;red_shift = 7;red_scale = 1;green_scale = 1;blue_scale = 8;}// offset can be bogus, be carefulif (offset >= 0 && startpos + offset > d->pos()) {if (!d->isSequential())d->seek(startpos + offset);// start of image data}int bpl = image.bytesPerLine();uchar *data = image.bits();if (nbits == 1) { // 1 bit BMP imagewhile (--h >= 0) {if (d->read((char*)(data + h*bpl), bpl) != bpl)break;}if (ncols == 2 && qGray(image.color(0)) < qGray(image.color(1)))swapPixel01(&image);// pixel 0 is white!}else if (nbits == 4) { // 4 bit BMP imageint buflen = ((w + 7) / 8) * 4;uchar *buf = new uchar[buflen];if (comp == BMP_RLE4) {// run length compressionint x = 0, y = 0, c, i;quint8 b;register uchar *p = data + (h - 1)*bpl;const uchar *endp = p + w;while (y < h) {if (!d->getChar((char *)&b))break;if (b == 0) { // escape codeif (!d->getChar((char *)&b) || b == 1) {y = h;// exit loop}else switch (b) {case 0: // end of linex = 0;y++;p = data + (h - y - 1)*bpl;break;case 2: // delta (jump){quint8 tmp;d->getChar((char *)&tmp);x += tmp;d->getChar((char *)&tmp);y += tmp;}// Protectionif ((uint)x >= (uint)w)x = w - 1;if ((uint)y >= (uint)h)y = h - 1;p = data + (h - y - 1)*bpl + x;break;default:// absolute mode// Protectionif (p + b > endp)b = endp - p;i = (c = b) / 2;while (i--) {d->getChar((char *)&b);*p++ = b >> 4;*p++ = b & 0x0f;}if (c & 1) {unsigned char tmp;d->getChar((char *)&tmp);*p++ = tmp >> 4;}if ((((c & 3) + 1) & 2) == 2)d->getChar(0); // align on word boundaryx += c;}}else { // encoded mode// Protectionif (p + b > endp)b = endp - p;i = (c = b) / 2;d->getChar((char *)&b);// 2 pixels to be repeatedwhile (i--) {*p++ = b >> 4;*p++ = b & 0x0f;}if (c & 1)*p++ = b >> 4;x += c;}}}else if (comp == BMP_RGB) {// no compressionmemset(data, 0, h*bpl);while (--h >= 0) {if (d->read((char*)buf, buflen) != buflen)break;register uchar *p = data + h*bpl;uchar *b = buf;for (int i = 0; i<w / 2; i++) { // convert nibbles to bytes*p++ = *b >> 4;*p++ = *b++ & 0x0f;}if (w & 1) // the last nibble*p = *b >> 4;}}delete[] buf;}else if (nbits == 8) { // 8 bit BMP imageif (comp == BMP_RLE8) {// run length compressionint x = 0, y = 0;quint8 b;register uchar *p = data + (h - 1)*bpl;const uchar *endp = p + w;while (y < h) {if (!d->getChar((char *)&b))break;if (b == 0) { // escape codeif (!d->getChar((char *)&b) || b == 1) {y = h;// exit loop}else switch (b) {case 0: // end of linex = 0;y++;p = data + (h - y - 1)*bpl;break;case 2: // delta (jump)// Protectionif ((uint)x >= (uint)w)x = w - 1;if ((uint)y >= (uint)h)y = h - 1;{quint8 tmp;d->getChar((char *)&tmp);x += tmp;d->getChar((char *)&tmp);y += tmp;}p = data + (h - y - 1)*bpl + x;break;default:// absolute mode// Protectionif (p + b > endp)b = endp - p;if (d->read((char *)p, b) != b)return false;if ((b & 1) == 1)d->getChar(0); // align on word boundaryx += b;p += b;}}else { // encoded mode// Protectionif (p + b > endp)b = endp - p;char tmp;d->getChar(&tmp);memset(p, tmp, b); // repeat pixelx += b;p += b;}}}else if (comp == BMP_RGB) {// uncompressedwhile (--h >= 0) {if (d->read((char *)data + h*bpl, bpl) != bpl)break;}}}else if (nbits == 16 || nbits == 24 || nbits == 32) { // 16,24,32 bit BMP imageregister QRgb *p;QRgb *end;uchar *buf24 = new uchar[bpl];int bpl24 = ((w*nbits + 31) / 32) * 4;uchar *b;int c;while (--h >= 0) {p = (QRgb *)(data + h*bpl);end = p + w;if (d->read((char *)buf24, bpl24) != bpl24)break;b = buf24;while (p < end) {c = *(uchar*)b | (*(uchar*)(b + 1) << 8);if (nbits != 16)c |= *(uchar*)(b + 2) << 16;*p++ = qRgb(((c & red_mask) >> red_shift) * red_scale,((c & green_mask) >> green_shift) * green_scale,((c & blue_mask) >> blue_shift) * blue_scale);b += nbits / 8;}}delete[] buf24;}if (bi.biHeight < 0) {// Flip the imageuchar *buf = new uchar[bpl];h = -bi.biHeight;for (int y = 0; y < h / 2; ++y) {memcpy(buf, data + y*bpl, bpl);memcpy(data + y*bpl, data + (h - y - 1)*bpl, bpl);memcpy(data + (h - y - 1)*bpl, buf, bpl);}delete[] buf;}return true;}static bool read_dib_bodyParitial(QDataStream &s, const BMP_INFOHDR &bi, int offset, int startpos, QImage &image, const QRect& rc, double dScalX, double dScalY){QIODevice* d = s.device();// if (d->atEnd()) // end of stream/file// return false;#if 0qDebug("offset...........%d", offset);qDebug("startpos.........%d", startpos);qDebug("biSize...........%d", bi.biSize);qDebug("biWidth..........%d", bi.biWidth);qDebug("biHeight.........%d", bi.biHeight);qDebug("biPlanes.........%d", bi.biPlanes);qDebug("biBitCount.......%d", bi.biBitCount);qDebug("biCompression....%d", bi.biCompression);qDebug("biSizeImage......%d", bi.biSizeImage);qDebug("biXPelsPerMeter..%d", bi.biXPelsPerMeter);qDebug("biYPelsPerMeter..%d", bi.biYPelsPerMeter);qDebug("biClrUsed........%d", bi.biClrUsed);qDebug("biClrImportant...%d", bi.biClrImportant);#endifint w = bi.biWidth, h = bi.biHeight, nbits = bi.biBitCount;int t = bi.biSize, comp = bi.biCompression;int red_mask = 0;int green_mask = 0;int blue_mask = 0;int red_shift = 0;int green_shift = 0;int blue_shift = 0;int red_scale = 0;int green_scale = 0;int blue_scale = 0;int ncols = 0;int depth = 0;QImage::Format format;switch (nbits) {case 32:case 24:case 16:depth = 32;format = QImage::Format_RGB32;break;case 8:case 4:depth = 8;format = QImage::Format_Indexed8;break;default:depth = 1;format = QImage::Format_Mono;}if (bi.biHeight < 0)h = -h; // support images with negative height// if(rc.bottom()>h||rc.right()>w){// return false;// }int w2 = rc.width();//w2= w;int h2 = rc.height();//h2= h;if (rc.bottom()>h) {h2 = h;}if (rc.right()>w) {w2 = w;}if (image.size() != QSize(w2, h2) || image.format() != format) {image = QImage(w2, h2, format);if (image.isNull()) // could not create imagereturn false;}if (depth != 32) {ncols = bi.biClrUsed ? bi.biClrUsed : 1 << nbits;if (ncols > 256) // sanity check - don't run out of mem if color table is brokenreturn false;image.setColorCount(ncols);}image.setDotsPerMeterX(bi.biXPelsPerMeter);image.setDotsPerMeterY(bi.biYPelsPerMeter);if (!d->isSequential())d->seek(startpos + BMP_FILEHDR_SIZE + (bi.biSize >= BMP_WIN4 ? BMP_WIN : bi.biSize)); // goto start of colormapif (bi.biSize >= BMP_WIN4 || (comp == BMP_BITFIELDS && (nbits == 16 || nbits == 32))) {if (d->read((char *)&red_mask, sizeof(red_mask)) != sizeof(red_mask))return false;if (d->read((char *)&green_mask, sizeof(green_mask)) != sizeof(green_mask))return false;if (d->read((char *)&blue_mask, sizeof(blue_mask)) != sizeof(blue_mask))return false;// Read BMP v4+ headerif (bi.biSize >= BMP_WIN4) {int alpha_mask = 0;int CSType = 0;int gamma_red = 0;int gamma_green = 0;int gamma_blue = 0;int endpoints[9];if (d->read((char *)&alpha_mask, sizeof(alpha_mask)) != sizeof(alpha_mask))return false;if (d->read((char *)&CSType, sizeof(CSType)) != sizeof(CSType))return false;if (d->read((char *)&endpoints, sizeof(endpoints)) != sizeof(endpoints))return false;if (d->read((char *)&gamma_red, sizeof(gamma_red)) != sizeof(gamma_red))return false;if (d->read((char *)&gamma_green, sizeof(gamma_green)) != sizeof(gamma_green))return false;if (d->read((char *)&gamma_blue, sizeof(gamma_blue)) != sizeof(gamma_blue))return false;if (bi.biSize == BMP_WIN5) {qint32 intent = 0;qint32 profileData = 0;qint32 profileSize = 0;qint32 reserved = 0;if (d->read((char *)&intent, sizeof(intent)) != sizeof(intent))return false;if (d->read((char *)&profileData, sizeof(profileData)) != sizeof(profileData))return false;if (d->read((char *)&profileSize, sizeof(profileSize)) != sizeof(profileSize))return false;if (d->read((char *)&reserved, sizeof(reserved)) != sizeof(reserved) || reserved != 0)return false;}}}if (ncols > 0) { // read color tableuchar rgb[4];int rgb_len = t == BMP_OLD ? 3 : 4;for (int i = 0; i<ncols; i++) {if (d->read((char *)rgb, rgb_len) != rgb_len)return false;image.setColor(i, qRgb(rgb[2], rgb[1], rgb[0]));if (d->atEnd()) // truncated filereturn false;}}else if (comp == BMP_BITFIELDS && (nbits == 16 || nbits == 32)) {red_shift = calc_shift(red_mask);red_scale = 256 / ((red_mask >> red_shift) + 1);green_shift = calc_shift(green_mask);green_scale = 256 / ((green_mask >> green_shift) + 1);blue_shift = calc_shift(blue_mask);blue_scale = 256 / ((blue_mask >> blue_shift) + 1);}else if (comp == BMP_RGB && (nbits == 24 || nbits == 32)) {blue_mask = 0x000000ff;green_mask = 0x0000ff00;red_mask = 0x00ff0000;blue_shift = 0;green_shift = 8;red_shift = 16;blue_scale = green_scale = red_scale = 1;}else if (comp == BMP_RGB && nbits == 16) {blue_mask = 0x001f;green_mask = 0x03e0;red_mask = 0x7c00;blue_shift = 0;green_shift = 2;red_shift = 7;red_scale = 1;green_scale = 1;blue_scale = 8;}// offset can be bogus, be carefulif (offset >= 0 && startpos + offset > d->pos()) {if (!d->isSequential())d->seek(startpos + offset);// start of image data}int bpl = image.bytesPerLine();unsigned char* data = image.bits();Q_ASSERT(data != NULL);if (nbits == 1) { // 1 bit BMP imagewhile (--h >= 0) {if (d->read((char*)(data + h*bpl), bpl) != bpl)break;}if (ncols == 2 && qGray(image.color(0)) < qGray(image.color(1)))swapPixel01(&image);// pixel 0 is white!}else if (nbits == 4) { // 4 bit BMP imageint buflen = ((w + 7) / 8) * 4;uchar *buf = new uchar[buflen];if (comp == BMP_RLE4) {// run length compressionint x = 0, y = 0, c, i;quint8 b;register uchar *p = data + (h - 1)*bpl;const uchar *endp = p + w;while (y < h) {if (!d->getChar((char *)&b))break;if (b == 0) { // escape codeif (!d->getChar((char *)&b) || b == 1) {y = h;// exit loop}else switch (b) {case 0: // end of linex = 0;y++;p = data + (h - y - 1)*bpl;break;case 2: // delta (jump){quint8 tmp;d->getChar((char *)&tmp);x += tmp;d->getChar((char *)&tmp);y += tmp;}// Protectionif ((uint)x >= (uint)w)x = w - 1;if ((uint)y >= (uint)h)y = h - 1;p = data + (h - y - 1)*bpl + x;break;default:// absolute mode// Protectionif (p + b > endp)b = endp - p;i = (c = b) / 2;while (i--) {d->getChar((char *)&b);*p++ = b >> 4;*p++ = b & 0x0f;}if (c & 1) {unsigned char tmp;d->getChar((char *)&tmp);*p++ = tmp >> 4;}if ((((c & 3) + 1) & 2) == 2)d->getChar(0); // align on word boundaryx += c;}}else { // encoded mode// Protectionif (p + b > endp)b = endp - p;i = (c = b) / 2;d->getChar((char *)&b);// 2 pixels to be repeatedwhile (i--) {*p++ = b >> 4;*p++ = b & 0x0f;}if (c & 1)*p++ = b >> 4;x += c;}}}else if (comp == BMP_RGB) {// no compressionmemset(data, 0, h*bpl);while (--h >= 0) {if (d->read((char*)buf, buflen) != buflen)break;register uchar *p = data + h*bpl;uchar *b = buf;for (int i = 0; i<w / 2; i++) { // convert nibbles to bytes*p++ = *b >> 4;*p++ = *b++ & 0x0f;}if (w & 1) // the last nibble*p = *b >> 4;}}delete[] buf;}else if (nbits == 8) { // 8 bit BMP imageif (comp == BMP_RLE8) {// run length compressionint x = 0, y = 0;quint8 b;register uchar *p = data + (h - 1)*bpl;const uchar *endp = p + w;while (y < h) {if (!d->getChar((char *)&b))break;if (b == 0) { // escape codeif (!d->getChar((char *)&b) || b == 1) {y = h;// exit loop}else switch (b) {case 0: // end of linex = 0;y++;p = data + (h - y - 1)*bpl;break;case 2: // delta (jump)// Protectionif ((uint)x >= (uint)w)x = w - 1;if ((uint)y >= (uint)h)y = h - 1;{quint8 tmp;d->getChar((char *)&tmp);x += tmp;d->getChar((char *)&tmp);y += tmp;}p = data + (h - y - 1)*bpl + x;break;default:// absolute mode// Protectionif (p + b > endp)b = endp - p;if (d->read((char *)p, b) != b)return false;if ((b & 1) == 1)d->getChar(0); // align on word boundaryx += b;p += b;}}else { // encoded mode// Protectionif (p + b > endp)b = endp - p;char tmp;d->getChar(&tmp);memset(p, tmp, b); // repeat pixelx += b;p += b;}}}else if (comp == BMP_RGB) {// uncompressedqint64 pos = d->pos();char* temp = new char[w + 1];if (qFuzzyCompare(dScalX, 1) && qFuzzyCompare(dScalY, 1)) {d->seek(pos + (h - rc.y() - h2) *w);// bplwhile (--h2 >= 0) {if (d->read(temp, w) != w)break;memcpy((char *)data + h2*bpl, temp + rc.x(), bpl);}}else {double yp = rc.y()*dScalY;int xp = rc.x();while (--h2 >= 0) {int hp = qRound(h2*dScalY);d->seek(pos + (h - yp - hp) *w);// bplif (d->read(temp, w) != w)break;char* p = (char *)data + h2*bpl;for (int i = 0; i<bpl; ++i) {int x = qRound((xp + i)*dScalX);if (x<w) {*(p + i) = *(temp + x);}else {*(p + i) = *(temp + w - 1);}}}}delete[]temp;}}else if (nbits == 16 || nbits == 24 || nbits == 32) { // 16,24,32 bit BMP imageregister QRgb *p;int bpl24 = ((w*nbits + 31) / 32) * 4;uchar *buf24 = new uchar[bpl24 + 1];memset(buf24, 0, bpl24 + 1);uchar *b;int c;qint64 pos = d->pos();QRgb *end;if (qFuzzyCompare(dScalX, 1) && qFuzzyCompare(dScalY, 1)) {d->seek(pos + (h - rc.y() - h2) *bpl24);// bplwhile (--h2 >= 0) {p = (QRgb *)(data + h2*bpl);end = p + w2;if (d->read((char *)buf24, bpl24) != bpl24)break;b = buf24;b += rc.x()*nbits / 8;// p += rc.x();while (p < end) {c = *(uchar*)b | (*(uchar*)(b + 1) << 8);if (nbits != 16)c |= *(uchar*)(b + 2) << 16;*p++ = qRgb(((c & red_mask) >> red_shift) * red_scale,((c & green_mask) >> green_shift) * green_scale,((c & blue_mask) >> blue_shift) * blue_scale);b += nbits / 8;}}}else {if (0) {//等距采样法，QT采用此方式，有一个缺点就是：缩小时未被选取的点的信息无法反映在缩小的图像上//，放大时会出现整个小块区域像素相同，图像不清晰的，特别是缩放比例很大时。while (--h2 >= 0) {d->seek(pos + (h - qRound((rc.y() + h2)*dScalX))*bpl24);// bplp = (QRgb *)(data + h2*bpl);end = p + w2;if (d->read((char *)buf24, bpl24) != bpl24)break;int startY = qCeil((rc.y() + h2)*dScalX);int endY = qFloor((rc.y() + h2 + 1)*dScalX);// qDebug()<<startY<<","<<endY;for (int i = 0; i<w2; ++i) {int offset = qRound((rc.x() + i)*dScalX)*nbits / 8;offset = offset >= bpl24 ? (bpl24 - 1) : offset;{b = buf24 + offset;c = *(uchar*)b | (*(uchar*)(b + 1) << 8);if (nbits != 16)c |= *(uchar*)(b + 2) << 16;*p++ = qRgb(((c & red_mask) >> red_shift) * red_scale,((c & green_mask) >> green_shift) * green_scale,((c & blue_mask) >> blue_shift) * blue_scale);}}}}if (0){// 双线性插值采样，解决上面缺点，但是速度会慢，查的数据多了啊h2 = rc.height();//h2= h;while (--h2 >= 0) {int startY = qRound((rc.y() + h2)*dScalX);int endY = qRound((rc.y() + h2 + 1)*dScalX);std::vector<std::string> datas;for (int i = startY; i<endY; ++i) {d->seek(pos + (h - qRound((rc.y() + h2)*dScalX))*bpl24);if (d->read((char *)buf24, bpl24) != bpl24)break;datas.push_back(std::string((char *)buf24, bpl24));}p = (QRgb *)(data + h2*bpl);for (int i = 0; i<w2; ++i) {int startX = qRound((rc.x() + i)*dScalX);int endX = qRound((rc.x() + i + 1)*dScalX);int total_red = 0;int total_green = 0;int total_blue = 0;int totalCount = 0;for (int j = startX; j<endX; ++j) {int offset = j*nbits / 8;for (int m = 0; m<datas.size(); ++m) {const std::string& rgbs = datas.at(m);if ((offset + 1)<rgbs.size()) {uchar a1 = rgbs.at(offset);uchar a2 = rgbs.at(offset + 1);uchar a3 = rgbs.at(2);c = (uchar)rgbs.at(offset) | ((uchar)rgbs.at(offset + 1) << 8);if (nbits != 16) {if ((offset + 2) >= rgbs.size())break;c |= (uchar)rgbs.at(offset + 2) << 16;}total_red += ((c & red_mask) >> red_shift) * red_scale;total_green += ((c & green_mask) >> green_shift) * green_scale;total_blue += ((c & blue_mask) >> blue_shift) * blue_scale;++totalCount;}else {break;}}}if (totalCount != 0) {*p = qRgb(total_red / totalCount,total_green / totalCount,total_blue / totalCount);}++p;}}}if (1) {//折中方案等距采样法，双线性插值采样太慢。while (--h2 >= 0) {d->seek(pos + (h - qRound((rc.y() + h2)*dScalX))*bpl24);// bplp = (QRgb *)(data + h2*bpl);end = p + w2;if (d->read((char *)buf24, bpl24) != bpl24)break;int startY = qCeil((rc.y() + h2)*dScalX);int endY = qFloor((rc.y() + h2 + 1)*dScalX);// qDebug()<<startY<<","<<endY;for (int i = 0; i<w2; ++i) {int startX = qRound((rc.x() + i)*dScalX);int endX = qRound((rc.x() + i + 1)*dScalX);int total_red = 0;int total_green = 0;int total_blue = 0;int totalCount = 0;for (int j = startX; j<endX; ++j) {int offset = j*nbits / 8;if (nbits != 16) {if ((offset + 2) >= bpl24)break;}else {if ((offset + 1) >= bpl24)break;}b = buf24 + offset;c = *(uchar*)b | (*(uchar*)(b + 1) << 8);if (nbits != 16)c |= *(uchar*)(b + 2) << 16;total_red += ((c & red_mask) >> red_shift) * red_scale;total_green += ((c & green_mask) >> green_shift) * green_scale;total_blue += ((c & blue_mask) >> blue_shift) * blue_scale;++totalCount;}if (totalCount != 0) {*p = qRgb(total_red / totalCount,total_green / totalCount,total_blue / totalCount);}++p;}}}}delete[] buf24;}if (bi.biHeight < 0) {// Flip the imageuchar *buf = new uchar[bpl];h = -bi.biHeight;for (int y = 0; y < h / 2; ++y) {memcpy(buf, data + y*bpl, bpl);memcpy(data + y*bpl, data + (h - y - 1)*bpl, bpl);memcpy(data + (h - y - 1)*bpl, buf, bpl);}delete[] buf;}return true;}// this is also used in qmime_win.cppbool qt_write_dib(QDataStream &s, QImage image){int nbits;int bpl_bmp;int bpl = image.bytesPerLine();QIODevice* d = s.device();if (!d->isWritable())return false;if (image.depth() == 8 && image.colorCount() <= 16) {bpl_bmp = (((bpl + 1) / 2 + 3) / 4) * 4;nbits = 4;}else if (image.depth() == 32) {bpl_bmp = ((image.width() * 24 + 31) / 32) * 4;nbits = 24;#ifdef Q_WS_QWS}else if (image.depth() == 1 || image.depth() == 8) {// Qt for Embedded Linux doesn't word align.bpl_bmp = ((image.width()*image.depth() + 31) / 32) * 4;nbits = image.depth();#endif}else {bpl_bmp = bpl;nbits = image.depth();}BMP_INFOHDR bi;bi.biSize = BMP_WIN;// build info headerbi.biWidth = image.width();bi.biHeight = image.height();bi.biPlanes = 1;bi.biBitCount = nbits;bi.biCompression = BMP_RGB;bi.biSizeImage = bpl_bmp*image.height();bi.biXPelsPerMeter = image.dotsPerMeterX() ? image.dotsPerMeterX(): 2834; // 72 dpi defaultbi.biYPelsPerMeter = image.dotsPerMeterY() ? image.dotsPerMeterY() : 2834;bi.biClrUsed = image.colorCount();bi.biClrImportant = image.colorCount();s << bi;// write info headerif (s.status() != QDataStream::Ok)return false;if (image.depth() != 32) {// write color tableuchar *color_table = new uchar[4 * image.colorCount()];uchar *rgb = color_table;QVector<QRgb> c = image.colorTable();for (int i = 0; i<image.colorCount(); i++) {*rgb++ = qBlue(c[i]);*rgb++ = qGreen(c[i]);*rgb++ = qRed(c[i]);*rgb++ = 0;}if (d->write((char *)color_table, 4 * image.colorCount()) == -1) {delete[] color_table;return false;}delete[] color_table;}if (image.format() == QImage::Format_MonoLSB)image = image.convertToFormat(QImage::Format_Mono);int y;if (nbits == 1 || nbits == 8) {// direct output#ifdef Q_WS_QWS// Qt for Embedded Linux doesn't word align.int pad = bpl_bmp - bpl;char padding[4];#endiffor (y = image.height() - 1; y >= 0; y--) {if (d->write((char*)image.scanLine(y), bpl) == -1)return false;#ifdef Q_WS_QWSif (d->write(padding, pad) == -1)return false;#endif}return true;}uchar *buf = new uchar[bpl_bmp];uchar *b, *end;register uchar *p;memset(buf, 0, bpl_bmp);for (y = image.height() - 1; y >= 0; y--) { // write the image bitsif (nbits == 4) { // convert 8 -> 4 bitsp = image.scanLine(y);b = buf;end = b + image.width() / 2;while (b < end) {*b++ = (*p << 4) | (*(p + 1) & 0x0f);p += 2;}if (image.width() & 1)*b = *p << 4;}else { // 32 bitsQRgb *p = (QRgb *)image.scanLine(y);QRgb *end = p + image.width();b = buf;while (p < end) {*b++ = qBlue(*p);*b++ = qGreen(*p);*b++ = qRed(*p);p++;}}if (bpl_bmp != d->write((char*)buf, bpl_bmp)) {delete[] buf;return false;}}delete[] buf;return true;}// this is also used in qmime_win.cppbool qt_read_dib(QDataStream &s, QImage &image){BMP_INFOHDR bi;if (!read_dib_infoheader(s, bi))return false;return read_dib_body(s, bi, -1, -BMP_FILEHDR_SIZE, image);}QBmpLoader::QBmpLoader(): state(Error), m_device(NULL){}void QBmpLoader::setDevice(QIODevice *device){this->m_device = device;}QIODevice* QBmpLoader::device() {return this->m_device;}bool QBmpLoader::setImagePath(QString imagePath) {this->imagePath = imagePath;QFile* pFile = new QFile(imagePath);pFile->open(QIODevice::ReadWrite);this->setDevice(pFile);return readHeader();}bool QBmpLoader::readHeader(){state = Error;QIODevice *d = device();QDataStream s(d);startpos = d->pos();qint64 size = d->size();// Intel byte orders.setByteOrder(QDataStream::LittleEndian);// read BMP file headerif (!read_dib_fileheader(s, fileHeader))return false;// read BMP info headerif (!read_dib_infoheader(s, infoHeader))return false;state = ReadHeader;return true;}bool QBmpLoader::read(QImage *image){if (state == Error)return false;if (!image) {qWarning("QBmpLoader::read: cannot read into null pointer");return false;}QIODevice *d = device();QDataStream s(d);// Intel byte orders.setByteOrder(QDataStream::LittleEndian);// read imageif (!read_dib_body(s, infoHeader, fileHeader.bfOffBits, startpos, *image))return false;state = Ready;return true;}bool QBmpLoader::read(QImage *image, const QRect& rc, double dScalX, double dScalY) {if (state == Error)return false;if (!image) {qWarning("QBmpLoader::read: cannot read into null pointer");return false;}QIODevice *d = device();QDataStream s(d);// Intel byte orders.setByteOrder(QDataStream::LittleEndian);QRect rc2 = rc;if (dScalX<1.0) {int l = rc2.left();int w = rc2.width();rc2.setLeft(l*dScalX);rc2.setWidth(w*dScalX);dScalX = 1.0;}if (dScalY<1.0) {int t = rc2.top();int h = rc2.height();rc2.setTop(t*dScalY);rc2.setHeight(h*dScalY);dScalY = 1.0;}// read imageif (!read_dib_bodyParitial(s, infoHeader, fileHeader.bfOffBits, startpos, *image, rc2, dScalX, dScalY))return false;if (image->size() != rc.size()) {*image = image->scaled(rc.size(), Qt::IgnoreAspectRatio, Qt::SmoothTransformation);}state = Ready;return true;}bool QBmpLoader::read(QImage *image, const QRect& rc) {return read(image, rc, 1.0, 100);}

加载图片cpp

QImageReader imageReader(url);QImage _image = QImage(1920, 1080, QImage::Format_ARGB32);QSize imageSize = imageReader.size();int imageWidth = imageSize.width();int imageHeight = imageSize.height();int imageWidthAfterScale = 1920;int imageHeightAfterScale = 1080;QBmpLoader* m_bmpLoader=new QBmpLoader();//表示是个大图，用BmpLoader进行加载if (imageSize.width() * imageSize.height() > 4096 * 2160){m_bmpLoader->setImagePath(url);int readTimes = imageSize.width() > imageSize.height() ? imageSize.width() / 4096 : imageSize.height() / 4096;if (readTimes < 2){readTimes = 2;}QImage* totalImage = new QImage(imageWidthAfterScale, imageHeightAfterScale,QImage::Format_RGB32);QPainter painter(totalImage);QImage* image = new QImage(1920, 1080, QImage::Format_RGB32);for (int i = 0; i < readTimes; ++i){for (int j = 0; j < readTimes; ++j){QRect rect(imageWidth / readTimes*i, imageHeight / readTimes*j, imageWidth / readTimes, imageHeight / readTimes);m_bmpLoader->read(image, rect);painter.drawImage(QRect(imageWidthAfterScale / readTimes*i,imageHeightAfterScale / readTimes*j, imageWidthAfterScale / readTimes, imageHeightAfterScale / readTimes), image->scaled(QSize(imageWidthAfterScale / readTimes, imageHeightAfterScale / readTimes), Qt::IgnoreAspectRatio, Qt::SmoothTransformation), QRect(0, 0, imageWidthAfterScale / readTimes, imageHeightAfterScale / readTimes));}}delete image;_image = (*totalImage);painter.end();delete totalImage;}delete m_bmpLoader;//最终结果便会保存在_image中

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