QT源码拾贝0-5（qimage和qpainter）
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目录
2. qpainter_p.h中SmallStack模板元结构体存放智能指针
3. qpainter.cpp的保存函数，状态对象赋值使用std::exchange函数
5. qpainter.cpp中QChar字节操作，使用u在字节前面
0 qt源码查看方法
使用vscode工具，加载qt源码路径，比如：C:\\Qt\\6.5.0\\Src
再按住ctrl+鼠标，可以方便查看引用函数的定义。
返回上次光标位置，使用快捷键Alt和方向左/右键
跳过单个变量，使用快捷键ctrl加方向左/右键
1. qimage.cpp中线程池使用方法
/*!
\\since 5.14
Applies the color transformation \\a transform to all pixels in the image.
*/
void QImage::applyColorTransform(const QColorTransform &transform)
if (transform.isIdentity())
return;
detach();
if (!d)
return;
if (pixelFormat().colorModel() == QPixelFormat::Indexed)
for (int i = 0; i < d->colortable.size(); ++i)
d->colortable[i] = transform.map(d->colortable[i]);
return;
QImage::Format oldFormat = format();
if (qt_fpColorPrecision(oldFormat))
if (oldFormat != QImage::Format_RGBX32FPx4 && oldFormat != QImage::Format_RGBA32FPx4
&& oldFormat != QImage::Format_RGBA32FPx4_Premultiplied)
convertTo(QImage::Format_RGBA32FPx4);
else if (depth() > 32)
if (oldFormat != QImage::Format_RGBX64 && oldFormat != QImage::Format_RGBA64
&& oldFormat != QImage::Format_RGBA64_Premultiplied)
convertTo(QImage::Format_RGBA64);
else if (oldFormat != QImage::Format_ARGB32 && oldFormat != QImage::Format_RGB32
&& oldFormat != QImage::Format_ARGB32_Premultiplied)
if (hasAlphaChannel())
convertTo(QImage::Format_ARGB32);
else
convertTo(QImage::Format_RGB32);
QColorTransformPrivate::TransformFlags flags = QColorTransformPrivate::Unpremultiplied;
switch (format())
case Format_ARGB32_Premultiplied:
case Format_RGBA64_Premultiplied:
case Format_RGBA32FPx4_Premultiplied:
flags = QColorTransformPrivate::Premultiplied;
break;
case Format_RGB32:
case Format_RGBX64:
case Format_RGBX32FPx4:
flags = QColorTransformPrivate::InputOpaque;
break;
case Format_ARGB32:
case Format_RGBA64:
case Format_RGBA32FPx4:
break;
default:
Q_UNREACHABLE();
std::function<void(int,int)> transformSegment;
if (qt_fpColorPrecision(format()))
transformSegment = [&](int yStart, int yEnd)
for (int y = yStart; y < yEnd; ++y)
QRgbaFloat32 *scanline = reinterpret_cast<QRgbaFloat32 *>(d->data + y * d->bytes_per_line);
QColorTransformPrivate::get(transform)->apply(scanline, scanline, width(), flags);
;
else if (depth() > 32)
transformSegment = [&](int yStart, int yEnd)
for (int y = yStart; y < yEnd; ++y)
QRgba64 *scanline = reinterpret_cast<QRgba64 *>(d->data + y * d->bytes_per_line);
QColorTransformPrivate::get(transform)->apply(scanline, scanline, width(), flags);
;
else
transformSegment = [&](int yStart, int yEnd)
for (int y = yStart; y < yEnd; ++y)
QRgb *scanline = reinterpret_cast<QRgb *>(d->data + y * d->bytes_per_line);
QColorTransformPrivate::get(transform)->apply(scanline, scanline, width(), flags);
;
#if QT_CONFIG(thread) && !defined(Q_OS_WASM)
int segments = (qsizetype(width()) * height()) >> 16;
segments = std::min(segments, height());
QThreadPool *threadPool = QThreadPool::globalInstance();
if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread()))
QSemaphore semaphore;
int y = 0;
for (int i = 0; i < segments; ++i)
int yn = (height() - y) / (segments - i);
threadPool->start([&, y, yn]()
transformSegment(y, y + yn);
semaphore.release(1);
);
y += yn;
semaphore.acquire(segments);
else
#endif
transformSegment(0, height());
if (oldFormat != format())
*this = std::move(*this).convertToFormat(oldFormat);
2. qpainter_p.h中SmallStack模板元结构体存放智能指针
std::unique_ptr<QPainterState> state;
template <typename T, std::size_t N = 8>
struct SmallStack : std::stack<T, QVarLengthArray<T, N>>
void clear() this->c.clear();
;
SmallStack<std::unique_ptr<QPainterState>> savedStates;
mutable std::unique_ptr<QPainterDummyState> dummyState;3. qpainter.cpp的保存函数，状态对象赋值使用std::exchange函数
void QPainter::save()
#ifdef QT_DEBUG_DRAW
if (qt_show_painter_debug_output)
printf("QPainter::save()\\n");
#endif
Q_D(QPainter);
if (!d->engine)
qWarning("QPainter::save: Painter not active");
return;
std::unique_ptr<QPainterState> prev;
if (d->extended)
// separate the creation of a new state from the update of d->state, since some
// engines access d->state directly (not via createState()'s argument)
std::unique_ptr<QPainterState> next(d->extended->createState(d->state.get()));
prev = std::exchange(d->state, std::move(next));
d->extended->setState(d->state.get());
else
d->updateState(d->state);
prev = std::exchange(d->state, std::make_unique<QPainterState>(d->state.get()));
d->engine->state = d->state.get();
d->savedStates.push(std::move(prev));
4. qpainter.cpp中获得类对象的方法
QBrush QPaintEngineState::brush() const
return static_cast<const QPainterState *>(this)->brush;
5. qpainter.cpp中QChar字节操作，使用u在字节前面
int old_offset = offset;
for (; offset < text.size(); offset++)
QChar chr = text.at(offset);
if (chr == u'\\r' || (singleline && chr == u'\\n'))
text[offset] = u' ';
else if (chr == u'\\n')
text[offset] = QChar::LineSeparator;
else if (chr == u'&')
++maxUnderlines;
else if (chr == u'\\t')
if (!expandtabs)
text[offset] = u' ';
else if (!tabarraylen && !tabstops)
tabstops = qRound(fm.horizontalAdvance(u'x')*8);
else if (chr == u'\\x9c')
// string with multiple length variants
hasMoreLengthVariants = true;
break;
QList<QTextLayout::FormatRange> underlineFormats;
int length = offset - old_offset;
if ((hidemnmemonic || showmnemonic) && maxUnderlines > 0)
QChar *cout = text.data() + old_offset;
QChar *cout0 = cout;
QChar *cin = cout;
int l = length;
while (l)
if (*cin == u'&')
++cin;
--length;
--l;
if (!l)
break;
if (*cin != u'&' && !hidemnmemonic && !(tf & Qt::TextDontPrint))
QTextLayout::FormatRange range;
range.start = cout - cout0;
range.length = 1;
range.format.setFontUnderline(true);
underlineFormats.append(range);
#ifdef Q_OS_MAC
else if (hidemnmemonic && *cin == u'(' && l >= 4 &&
cin[1] == u'&' && cin[2] != u'&' &&
cin[3] == u')')
int n = 0;
while ((cout - n) > cout0 && (cout - n - 1)->isSpace())
++n;
cout -= n;
cin += 4;
length -= n + 4;
l -= 4;
continue;
#endif //Q_OS_MAC
*cout = *cin;
++cout;
++cin;
--l;
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