c++ - Qt- 改变 QPixmap 的不透明度

Question

如何改变QPixmap的不透明度？

我已经将图像设置为背景实际上我想改变它的不透明度，这是我的代码:

调用.h:

private:
    QPixmap m_avatar;

调用.cpp:

void Call::resizeEvent(QResizeEvent *e)
{
    QPalette pal = palette();
    pal.setBrush(backgroundRole(), m_avatar.scaled(e->size(), Qt::IgnoreAspectRatio, Qt::SmoothTransformation));
    setPalette(pal);
}

我已经更改了 resizeEvent 函数，但它不会更改背景的不透明度。

void Call::resizeEvent(QResizeEvent *e)
{
    QPixmap result_avatar(m_avatar.size());
    result_avatar.fill(Qt::transparent);
    QPainter painter;
    painter.setOpacity(0.5);
    painter.begin(&result_avatar);
    painter.drawPixmap(0, 0, m_avatar);
    painter.end();
    QPalette pal = palette();
    pal.setBrush(backgroundRole(), result_avatar.scaled(e->size(), Qt::IgnoreAspectRatio, Qt::SmoothTransformation));
    setPalette(pal);
}

有什么建议吗？

Answer 1

您没有使用本地 QPainter 对象。根据QWidget Events :

paintEvent() is called whenever the widget needs to be repainted. Every widget displaying custom content must implement it. Painting using a QPainter can only take place in a paintEvent() or a function called by a paintEvent().

这里有效:

void Call::paintEvent(QPaintEvent *)
{
    // create a new object scaled to widget size
    QPixmap result_avatar = m_avatar.scaled(size());

    QPainter painter(this);
    painter.setOpacity(0.5);
    // use scaled image or if needed not scaled m_avatar
    painter.drawPixmap(0, 0, result_avatar);
}

---

pixmap case 绘画更新

如果只需要使用 QPainter 在像素图上绘制一些不透明度，则必须仅在通过 QPainter::begin 激活 QPainter 之后设置不透明度()。因此，在更改顺序后，像素图 result_avatar 有两个图像(一个调整大小后不透明度为 1，原始像素图在顶部，不透明度为 0.5):

QPainter painter;
painter.begin(&result_avatar);
painter.setOpacity(0.5);
painter.drawPixmap(0, 0, m_avatar);
painter.end()