Loading...

XML

Word

Printable

Details

Type: Bug
Resolution: Done
Priority: P2: Important
Fix Version/s: 5.6.3
Affects Version/s: 5.6.0
Component/s: GUI: Painting
Labels:
None
Environment:
Windows 10

Description

Using QPainter::drawTiledPixmap with a pixmap width > 2048 causes the image to repeat after 2048 pixel instead of after the actual width. The following sample triggers this (you need a big enough screen to stretch to the window to over 2048 pixel width in logical space. See also the attached image.

#include <QtGui>
#include <QWidget>
#include <QApplication>
class QTestWidget : public QWidget
{
	virtual void paintEvent(QPaintEvent* event) override
	{
		QPainter painter(this);
		const QRect rect = contentsRect();
		QImage img(rect.width(), 1, QImage::Format_ARGB32);
		for (int x = 0; x < img.width(); ++x)
		{
			QColor color = QColor::fromHslF((double)x / img.width(), 1, 0.5);
			img.setPixel(x, 0, color.rgba());
		}

		QImage img565 = img.convertToFormat(QImage::Format_RGB16);
		{
			QPainter painter565(&img565);
			QBrush brush(img565);
			// Triggers blend_tiled_rgb565 opague bug
			painter565.fillRect(rect.adjusted(0, 0, 0, -rect.width() / 2), brush);
		}

		painter.drawTiledPixmap(rect.adjusted(0, rect.height() / 2, 0, 0), QPixmap::fromImage(img565));
		// Triggers blend_tiled_argb bug
		painter.drawTiledPixmap(rect.adjusted(0, 0, 0, -rect.height() / 2), QPixmap::fromImage(img));
	}
};

int main(int argc, char *argv[])
{
	QApplication app(argc, argv);
	QTestWidget test;
	test.show();
	return qApp->exec();
}

The error is in the function blend_tiled_argb in qdrawhelper.cpp:

while (length) {
            int l = qMin(image_width - sx, length);
            if (buffer_size < l)
                l = buffer_size;
            const uint *src = (const uint *)data->texture.scanLine(sy) + sx;
            uint *dest = ((uint *)data->rasterBuffer->scanLine(spans->y)) + x;
            op.func(dest, src, l, coverage);
            x += l;
            length -= l;
            sx = 0;
}

Should be replaced with:

while (length) {
            int l = qMin(image_width - sx, length);
            if (buffer_size < l)
                l = buffer_size;
            const uint *src = (const uint *)data->texture.scanLine(sy) + sx;
            uint *dest = ((uint *)data->rasterBuffer->scanLine(spans->y)) + x;
            op.func(dest, src, l, coverage);
            x += l;
            sx += l;
            length -= l;
            if (sx >= image_width)
                sx = 0;
}

This way it would function the same as e.g. blend_tiled_generic_rgb64 above it in the same file. The same pattern is also used incorrectly in blend_tiled_rgb565. I've tested both on the current dev branch and the problem exists there as well.