[SOLVED] QImage setPixel alpha issue

[bunjee]

Hi,

I'm replacing pixels in a QImage using that code :

for (int i = 0; i < height; i++)
	{
		for (int j = 0; j < width; j++)
		{
			int alpha = qAlpha(image.pixel(j, i));
			if (alpha > 0)
			{
				image.setPixel(j, i,
						qRgba(color.red(),
							  color.green(),
							  color.blue(),
							  alpha));
			}
		}
	}
 
q->QPixmap::operator=(QPixmap::fromImage(image));

for (int i = 0; i < height; i++)
	{
		for (int j = 0; j < width; j++)
		{
			int alpha = qAlpha(image.pixel(j, i));
			if (alpha > 0)
			{
				image.setPixel(j, i,
						qRgba(color.red(),
							  color.green(),
							  color.blue(),
							  alpha));
			}
		}
	}

q->QPixmap::operator=(QPixmap::fromImage(image));

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My image file is a PNG file.

For some reason, everytime I replace a "transparent" pixel. The pixel goes black instead of the choosen color. Plain pixels are replaced fine.

Any idea ?

[bunjee]

Solved.

QImage dissociates alpha and RGB channel.

void qkColorPixmapPrivate::refreshPixmap(const QColor & color)
{
	Q_Q(qkColorPixmap);
 
	if (this->color == color) return;
 
	QImage image = basePixmap.toImage();
	QImage alpha = image.alphaChannel();
 
	int width = basePixmap.width();
	int height = basePixmap.height();
 
	for (int i = 0; i < height; i++)
	{
		for (int j = 0; j < width; j++)
		{
			int a = qAlpha(image.pixel(j, i));
			if (a > 0)
			{
				image.setPixel(j, i,
						qRgb(color.red(),
							 color.green(),
							 color.blue()));
 
				alpha.setPixel(j, i, a);
			}
		}
	}
 
	image.setAlphaChannel(alpha);
 
	q->QPixmap::operator=(QPixmap::fromImage(image));
 
	this->color = color;
}

void qkColorPixmapPrivate::refreshPixmap(const QColor & color)
{
	Q_Q(qkColorPixmap);

	if (this->color == color) return;

	QImage image = basePixmap.toImage();
	QImage alpha = image.alphaChannel();

	int width = basePixmap.width();
	int height = basePixmap.height();

	for (int i = 0; i < height; i++)
	{
		for (int j = 0; j < width; j++)
		{
			int a = qAlpha(image.pixel(j, i));
			if (a > 0)
			{
				image.setPixel(j, i,
						qRgb(color.red(),
							 color.green(),
							 color.blue()));

				alpha.setPixel(j, i, a);
			}
		}
	}

	image.setAlphaChannel(alpha);

	q->QPixmap::operator=(QPixmap::fromImage(image));

	this->color = color;
}

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