使用一个QGraphicsScene
不会改善事情 - 它是一个额外的层QWidget
。您追求的是原始性能,所以您不应该使用它。
你可以实施一个QTextDocument
作为内存缓冲区/文件的可见部分的视图模型,但绘制新的QTextDocument
每次滚动不会比直接在屏幕上绘制东西快QWidget
.
Using QStaticText
是朝着正确方向迈出的一步,但还不够:渲染QStaticText
仍然需要字形形状的光栅化。您可以做得更好并缓存每个的像素图QChar, QColor
您希望渲染的组合:这比光栅化字符轮廓要快得多,无论是否使用QStaticText
or not.
然后,您可以从缓存中绘制像素图,而不是绘制单个字符。这次提交演示了这种方法。人物绘制方法为:
void drawChar(const QPointF & pos, QChar ch, QColor color, QPainter & p) {
auto & glyph = m_cache[{ch, color}];
if (glyph.isNull()) {
glyph = QPixmap{m_glyphRect.size().toSize()};
glyph.fill(Qt::white);
QPainter p{&glyph};
p.setPen(color);
p.setFont(m_font);
p.drawText(m_glyphPos, {ch});
}
p.drawPixmap(pos, glyph);
}
您还可以缓存每个(字符,前景,背景)元组。唉,当有很多前景/背景组合时,这种情况很快就会失控。
如果所有背景都是相同的颜色(例如白色),您希望存储角色的负掩码:glyph
具有白色背景和透明形状。这次提交演示了这种方法。字形矩形填充字形颜色,然后在顶部应用白色蒙版:
void drawChar(const QPointF & pos, QChar ch, QColor color, QPainter & p) {
auto & glyph = m_glyphs[ch];
if (glyph.isNull()) {
glyph = QImage{m_glyphRect.size().toSize(), QImage::Format_ARGB32_Premultiplied};
glyph.fill(Qt::white);
QPainter p{&glyph};
p.setCompositionMode(QPainter::CompositionMode_DestinationOut);
p.setFont(m_font);
p.drawText(m_glyphPos, {ch});
}
auto rect = m_glyphRect;
rect.moveTo(pos);
p.fillRect(rect, color);
p.drawImage(pos, glyph);
}
您可以只存储 alpha 遮罩并按需合成它们,而不是存储给定颜色的完全预渲染的字符:
- 从透明背景上预渲染的白色字形开始(
CompositionMode_Source
).
- 用背景填充字形矩形
CompositionMode_SourceOut
:背景将保留角色本身的孔。
- 用前景填充字形矩形
CompositionMode_DestinationOver
:前景将填补这个洞。
- (可选)如果您尚未在小部件上绘制,则在小部件上绘制合成。
事实证明,这相当快,并且渲染是完全可并行的 - 请参阅下面的示例。
注意:预渲染的字形可以使用颜色与 Alpha 的进一步预乘来显得不那么粗。
另一种具有出色性能的方法是使用 GPU 模拟文本模式显示。将预渲染的字形轮廓存储在纹理中,将要渲染的字形索引和颜色存储在数组中,并使用 OpenGL 和两个着色器进行渲染。这个例子可能是实施这种方法的起点。
下面是一个使用 CPU 跨多个线程渲染的完整示例。
我们从后备存储视图开始,用于生成QImage
是给定小部件的后备存储的视图,可用于并行绘制。
在 2013 iMac 上,此代码在大约 8 毫秒内重新绘制全屏小部件。
// https://github.com/KubaO/stackoverflown/tree/master/questions/hex-widget-40458515
#include <QtConcurrent>
#include <QtWidgets>
#include <algorithm>
#include <array>
#include <cmath>
struct BackingStoreView {
QImage *dst = {};
uchar *data = {};
const QWidget *widget = {};
explicit BackingStoreView(const QWidget *widget) {
if (!widget || !widget->window()) return;
dst = dynamic_cast<QImage*>(widget->window()->backingStore()->paintDevice());
if (!dst || dst->depth() % 8) return;
auto byteDepth = dst->depth()/8;
auto pos = widget->mapTo(widget->window(), {});
data = const_cast<uchar*>(dst->constScanLine(pos.y()) + byteDepth * pos.x());
this->widget = widget;
}
// A view onto the backing store of a given widget
QImage getView() const {
if (!data) return {};
QImage ret(data, widget->width(), widget->height(), dst->bytesPerLine(), dst->format());
ret.setDevicePixelRatio(widget->devicePixelRatio());
return ret;
}
// Is a given image exactly this view?
bool isAView(const QImage &img) const {
return data && img.bits() == data && img.depth() == dst->depth()
&& img.width() == widget->width() && img.height() == widget->height()
&& img.bytesPerLine() == dst->bytesPerLine() && img.format() == dst->format();
}
};
然后,CP437字符集:
static auto const CP437 = QStringLiteral(
" ☺☻♥♦♣♠•◘○◙♂♀♪♫☼▶◀↕‼¶§▬↨↑↓→←∟↔▲▼"
"␣!\"#$%&'()*+,-./0123456789:;<=>?"
"@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_"
"`abcdefghijklmnopqrstuvwxyz{|}~ "
"ÇüéâäàåçêëèïîìÄÅÉæÆôöòûùÿÖÜ¢£¥₧ƒ"
"áíóúñѪº¿⌐¬½¼¡«»░▒▓│┤╡╢╖╕╣║╗╝╜╛┐"
"└┴┬├─┼╞╟╚╔╩╦╠═╬╧╨╤╥╙╘╒╓╫╪┘┌█▄▌▐▀"
"αßΓπΣσµτΦΘΩδ∞φε∩≡±≥≤⌠⌡÷≈°∙·√ⁿ²■ ");
The HexView
小部件源自QAbstractScrollArea
并可视化内存映射的数据块:
class HexView : public QAbstractScrollArea {
Q_OBJECT
QImage const m_nullImage;
const int m_addressChars = 8;
const int m_dataMargin = 4;
const char * m_data = {};
size_t m_dataSize = 0;
size_t m_dataStart = 0;
QSize m_glyphSize;
QPointF m_glyphPos;
int m_charsPerLine, m_lines;
QMap<QChar, QImage> m_glyphs;
QFont m_font{"Monaco"};
QFontMetricsF m_fm{m_font};
struct DrawUnit { QPoint pos; const QImage *glyph; QColor fg, bg; };
QFutureSynchronizer<void> m_sync;
QVector<DrawUnit> m_chunks;
QVector<QImage> m_stores;
using chunk_it = QVector<DrawUnit>::const_iterator;
using store_it = QVector<QImage>::const_iterator;
static inline QChar decode(char ch) { return CP437[uchar(ch)]; }
inline int xStep() const { return m_glyphSize.width(); }
inline int yStep() const { return m_glyphSize.height(); }
void initData() {
int const width = viewport()->width() - m_addressChars*xStep() - m_dataMargin;
m_charsPerLine = (width > 0) ? width/xStep() : 0;
m_lines = viewport()->height()/yStep();
if (m_charsPerLine && m_lines) {
verticalScrollBar()->setRange(0, m_dataSize/m_charsPerLine);
verticalScrollBar()->setValue(m_dataStart/m_charsPerLine);
} else {
verticalScrollBar()->setRange(0, 0);
}
}
const QImage &glyph(QChar ch) {
auto &glyph = m_glyphs[ch];
if (glyph.isNull()) {
QPointF extent = m_fm.boundingRect(ch).translated(m_glyphPos).bottomRight();
glyph = QImage(m_glyphSize, QImage::Format_ARGB32_Premultiplied);
glyph.fill(Qt::transparent);
QPainter p{&glyph};
p.setPen(Qt::white);
p.setFont(m_font);
p.translate(m_glyphPos);
p.scale(std::min(1.0, (m_glyphSize.width()-1)/extent.x()),
std::min(1.0, (m_glyphSize.height()-1)/extent.y()));
p.drawText(QPointF{}, {ch});
}
return glyph;
}
并行渲染是在类方法中完成的 - 除了访问只读数据和渲染到后备存储之外,它们不会修改小部件的状态。每个线程都作用于存储中的隔离线。
static void drawChar(const DrawUnit & u, QPainter &p) {
const QRect rect(u.pos, u.glyph->size());
p.setCompositionMode(QPainter::CompositionMode_Source);
p.drawImage(u.pos, *u.glyph);
p.setCompositionMode(QPainter::CompositionMode_SourceOut);
p.fillRect(rect, u.bg);
p.setCompositionMode(QPainter::CompositionMode_DestinationOver);
p.fillRect(rect, u.fg);
}
static QFuture<void> submitChunks(chunk_it begin, chunk_it end, store_it store) {
return QtConcurrent::run([begin, end, store]{
QPainter p(const_cast<QImage*>(&*store));
for (auto it = begin; it != end; it++)
drawChar(*it, p);
});
}
此方法在线程之间分配工作块:
int processChunks() {
m_stores.resize(QThread::idealThreadCount());
BackingStoreView view(viewport());
if (!view.isAView(m_stores.last()))
std::generate(m_stores.begin(), m_stores.end(), [&view]{ return view.getView(); });
std::ptrdiff_t jobSize = std::max(128, (m_chunks.size() / m_stores.size())+1);
auto const cend = m_chunks.cend();
int refY = 0;
auto store = m_stores.cbegin();
for (auto it = m_chunks.cbegin(); it != cend;) {
auto end = it + std::min(cend-it, jobSize);
while (end != cend && (end->pos.y() == refY || (refY = end->pos.y(), false)))
end++; // break chunks across line boundaries
m_sync.addFuture(submitChunks(it, end, store));
it = end;
store++;
}
m_sync.waitForFinished();
m_sync.clearFutures();
m_chunks.clear();
return store - m_stores.cbegin();
}
其余的实现是没有争议的:
protected:
void paintEvent(QPaintEvent *ev) override {
QElapsedTimer time;
time.start();
QPainter p{viewport()};
QPoint pos;
QPoint const step{xStep(), 0};
auto dividerX = m_addressChars*xStep() + m_dataMargin/2.;
p.drawLine(dividerX, 0, dividerX, viewport()->height());
int offset = 0;
QRect rRect = ev->rect();
p.end();
while (offset < m_charsPerLine*m_lines && m_dataStart + offset < m_dataSize) {
const auto address = QString::number(m_dataStart + offset, 16);
pos += step * (m_addressChars - address.size());
for (auto c : address) {
if (QRect(pos, m_glyphSize).intersects(rRect))
m_chunks.push_back({pos, &glyph(c), Qt::black, Qt::white});
pos += step;
}
pos += {m_dataMargin, 0};
auto bytes = std::min(m_dataSize - offset, (size_t)m_charsPerLine);
for (int n = bytes; n; n--) {
if (QRect(pos, m_glyphSize).intersects(rRect))
m_chunks.push_back({pos, &glyph(decode(m_data[m_dataStart + offset])), Qt::red, Qt::white});
pos += step;
offset ++;
}
pos = {0, pos.y() + yStep()};
}
int jobs = processChunks();
newStatus(QStringLiteral("%1ms n=%2").arg(time.nsecsElapsed()/1e6).arg(jobs));
}
void resizeEvent(QResizeEvent *) override {
initData();
}
void scrollContentsBy(int, int dy) override {
m_dataStart = verticalScrollBar()->value() * (size_t)m_charsPerLine;
viewport()->scroll(0, dy * m_glyphSize.height(), viewport()->rect());
}
public:
HexView(QWidget * parent = nullptr) : HexView(nullptr, 0, parent) {}
HexView(const char * data, size_t size, QWidget * parent = nullptr) :
QAbstractScrollArea{parent}, m_data(data), m_dataSize(size)
{
QRectF glyphRectF{0., 0., 1., 1.};
for (int i = 0x20; i < 0xE0; ++i)
glyphRectF = glyphRectF.united(m_fm.boundingRect(CP437[i]));
m_glyphPos = -glyphRectF.topLeft();
m_glyphSize = QSize(std::ceil(glyphRectF.width()), std::ceil(glyphRectF.height()));
initData();
}
void setData(const char * data, size_t size) {
if (data == m_data && size == m_dataSize) return;
m_data = data;
m_dataSize = size;
m_dataStart = 0;
initData();
viewport()->update();
}
Q_SIGNAL void newStatus(const QString &);
};
我们利用现代 64 位系统并对源文件进行内存映射,以便通过小部件进行可视化。出于测试目的,还提供了字符集视图:
int main(int argc, char ** argv) {
QApplication app{argc, argv};
QFile file{app.applicationFilePath()};
if (!file.open(QIODevice::ReadOnly)) return 1;
auto *const map = (const char*)file.map(0, file.size(), QFile::MapPrivateOption);
if (!map) return 2;
QWidget ui;
QGridLayout layout{&ui};
HexView view;
QRadioButton exe{"Executable"};
QRadioButton charset{"Character Set"};
QLabel status;
layout.addWidget(&view, 0, 0, 1, 4);
layout.addWidget(&exe, 1, 0);
layout.addWidget(&charset, 1, 1);
layout.addWidget(&status, 1, 2, 1, 2);
QObject::connect(&exe, &QPushButton::clicked, [&]{
view.setData(map, (size_t)file.size());
});
QObject::connect(&charset, &QPushButton::clicked, [&]{
static std::array<char, 256> data;
std::iota(data.begin(), data.end(), char(0));
view.setData(data.data(), data.size());
});
QObject::connect(&view, &HexView::newStatus, &status, &QLabel::setText);
charset.click();
ui.resize(1000, 800);
ui.show();
return app.exec();
}
#include "main.moc"