Event() : 事件處理器，每一個都對應一種型別的事件

When invoking paintEvent()

• In widget first displaying , system will generate a paint event
• In adjusting widget size, system will also generate a paint event
• In widget hiding and emerging, system will paint hiding area

Two methods for painting

void IconEditor::paintEvent(QPainEvent *event)
{
	QPainter painter(this);
	if (zoom >= 3)
	{
		painter.setPen(palette().foreground().color()); // 使用調色盤設定顏色
		for (int i = 0; i <= image.width(); ++i) // vertical line
		{
			painter.drawline
 
(zoom * i, 0, zoom * i, zoom * image.height());  
			/* 左邊兩個為座標起點，右邊兩個為座標終點 */
			/* Qt視窗部件左上角處的位置座標為（0，0） */
		}
		for (int j = 0; j <= image.height(); ++j) // horizontal line
		{
			painter.drawline(0, zoom * j, zoom * image.width(), zoom * j);
		}
		for (int i = 0; i < image.width(); ++i)
		{
			for (int
 
 j = 0; j < image.height(); ++j)
			{
				QRect rect = pixelRect(i, j);
				if (!event->region().intersect(rect).isEmpty())
				{
					QColor color = QColor::fromRgba(image.pixel(i, j));
					if (color.alpha() < 255) // paint background
						painter.fillRect(rect, Qt::White);
					painter.fillRect(rect, color); // fill rectangular
				}
			}
		}
	}
}

QRect IconEditor::pixelRect(int i, int j) const
{
	if (zoom >= 3)
	{
		return QRect(zoom * i + 1, zoom * j + 1, zoom - 1, zoom - 1);
		// QRect(x, y, width, height)
	}
	else
	{
		return QRect(zoom * i, zoom * j, zoom, zoom);
	}
}

Three Color Groups of Palette（調色盤）

• Active（啟用組） supply in current active windows’s widgets
• Inactive（非啟用組） supply in other window’s widgets
• Disabled（不可用組） supply in disabled widgets

void IconEditor::mousePressEvent(QMouseEvent *event)
{
	if (event->button() == Qt::LeftButton)
	{
		setImagePixel(event->pos(), true);
	}
	else if (event->button() == Qt::RightButton)
	{
		setImagePixel(event->pos(), false);
	}
}

void IconEditor::mouseMoveEvent(QMouseEvent *event)
{
	/*
		若是同時按下多個鍵，最終結果實際為QMouseEvent::buttons()
		的返回值與滑鼠的按鍵按照位或（|）運算的結果，因此需要
		位與（&）來判斷是否按下某個特定鍵
	*/
	if (event->button() & Qt::LeftButton)
	{
		setImagePixel(event->pos(), true);
	}
	else if (event->button() & Qt::RightButton)
	{
		setImagePixel(event->pos(), false);
	}
}

void IconEditor::setImagePixel(const QPoint &pos, bool opaque) 
{
	int i = pos.x() / zoom;
	int j = pos.y() / zoom;
	
	if (image.rect().contains(i, j))
	{
		if (opaque) // opaque（不透明的）
		{
			image.setPixel(i, j, penColor().rgba());
		}
		else
		{
			image.setPixel(i, j, qRgba(0, 0, 0, 0));
		}

		update(pixelRect(i, j);
	}
}