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Clementine-audio-player-Mac-Linux-Windows
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Code Issues Releases Wiki Activity

Double buffer nyanalayzer cat drawing - trying to draw a pixmap into itself produces weird artifacts in Qt 4.8

This commit is contained in:
David Sansome 2011-12-01 17:29:27 +00:00
parent 782c4ad460
commit 0d2dd452e2
2 changed files with 18 additions and 9 deletions
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24
src/analyzers/nyancatanalyzer.cpp
View File

@ -32,6 +32,7 @@ NyanCatAnalyzer::NyanCatAnalyzer(QWidget* parent)
cat_(":/nyancat.png"),
timer_id_(startTimer(kFrameIntervalMs)),
frame_(0),
current_buffer_(0),
available_rainbow_width_(0),
px_per_frame_(0),
x_offset_(0),
@ -65,7 +66,8 @@ void NyanCatAnalyzer::timerEvent(QTimerEvent* e) {
void NyanCatAnalyzer::resizeEvent(QResizeEvent* e) {
// Invalidate the buffer so it's recreated from scratch in the next paint
// event.
buffer_ = QPixmap();
buffer_[0] = QPixmap();
buffer_[1] = QPixmap();
available_rainbow_width_ = width() - kCatWidth + kRainbowOverlap;
px_per_frame_ = float(available_rainbow_width_) / (kHistorySize-1) + 1;
@ -118,22 +120,28 @@ void NyanCatAnalyzer::analyze(QPainter& p, const Analyzer::Scope& s, bool new_fr
}
// Do we have to draw the whole rainbow into the buffer?
if (buffer_.isNull()) {
buffer_ = QPixmap(QSize(width() + x_offset_, height()));
buffer_.fill(background_brush_.color());
if (buffer_[0].isNull()) {
for (int i=0 ; i<2 ; ++i) {
buffer_[i] = QPixmap(QSize(width() + x_offset_, height()));
buffer_[i].fill(background_brush_.color());
}
current_buffer_ = 0;
QPainter buffer_painter(&buffer_);
QPainter buffer_painter(&buffer_[0]);
buffer_painter.setRenderHint(QPainter::Antialiasing);
for (int band=kRainbowBands-1 ; band>=0 ; --band) {
buffer_painter.setPen(colors_[band]);
buffer_painter.drawPolyline(&polyline[band*kHistorySize], kHistorySize);
}
} else {
const int last_buffer = current_buffer_;
current_buffer_ = (current_buffer_ + 1) % 2;
// We can just shuffle the buffer along a bit and draw the new frame's data.
QPainter buffer_painter(&buffer_);
QPainter buffer_painter(&buffer_[current_buffer_]);
buffer_painter.setRenderHint(QPainter::Antialiasing);
buffer_painter.drawPixmap(0, 0, buffer_,
buffer_painter.drawPixmap(0, 0, buffer_[last_buffer],
px_per_frame_, 0,
x_offset_ + available_rainbow_width_ - px_per_frame_, 0);
buffer_painter.fillRect(x_offset_ + available_rainbow_width_ - px_per_frame_, 0,
@ -148,7 +156,7 @@ void NyanCatAnalyzer::analyze(QPainter& p, const Analyzer::Scope& s, bool new_fr
}
// Draw the buffer on to the widget
p.drawPixmap(0, 0, buffer_, x_offset_, 0, 0, 0);
p.drawPixmap(0, 0, buffer_[current_buffer_], x_offset_, 0, 0, 0);
// Draw nyan cat (he's been waiting for this for 75 lines).
// Nyan nyan nyan nyan.

3
src/analyzers/nyancatanalyzer.h
View File

@ -70,7 +70,8 @@ private:
float history_[kHistorySize * kRainbowBands];
// A cache of the last frame's rainbow, so it can be used in the next frame.
QPixmap buffer_;
QPixmap buffer_[2];
int current_buffer_;
// Geometry information that's updated on resize:
// The width of the widget minus the space for the cat