Qt QImage写入透明通道
开发Thinkvd中的player,设置透明度用的是sdl来实现的,转换中的水印用的是png, 如何设置水印的透明度,实际上要求把图片转换成带alpha的32位即可。
实现代码:
//! [8]
void ImageComposer::recalculateResult()
{
int alpha = 100;
QPainter::CompositionMode mode = currentMode();
QPainter painter(&resultImage);
painter.setCompositionMode(QPainter::CompositionMode_Source);
painter.fillRect(resultImage.rect(), Qt::transparent);
painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
//painter.drawImage(0, 0, destinationImage);
//painter.setCompositionMode(mode);
painter.drawImage(0, 0, sourceImage);
//painter.setCompositionMode(QPainter::CompositionMode_DestinationOver);
//painter.fillRect(resultImage.rect(), Qt::white);
//painter.fillRect(resultImage.rect(), QColor(0, 0, 0, alpha));
painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);
painter.fillRect(resultImage.rect(), QColor(0, 0, 0, alpha));
painter.end();
resultImage.save("f:/tmp/dddd.png");
resultLabel->setPixmap(QPixmap::fromImage(resultImage));
}
注意:
1. painter.setCompositionMode(QPainter::CompositionMode_DestinationIn);不能少
2. painter.drawImage与 painter.fillRect(resultImage.rect(), QColor(0, 0, 0, alpha));顺序.