[SOLVED] How is background grid drawn in Qt 4.8 undo example (see screenshot) ?

EdOfTheMountain

I am need to create a drawing app that supports undo and a grid that can be scaled to meters, or feet.

How is the background grid drawn in the Qt 4.8 Undo example?

http://qt-project.org/doc/qt-4.8/demos-undo.html

See screen shot below:

!http://qt-project.org/doc/qt-4.8/images/undodemo.png(Screenshot Qt4.8 Undo Example)!

Thanks in advance,

-Ed

Eddy

Have a look at the sources.

@
pal.setBrush(QPalette::Base, QPixmap(":/icons/background.png"));
@

EdOfTheMountain

How does the background.png image, which is a 20 pixel x 20 pixel white block, create a blue grid pattern on a white background?

@
/******************************************************************************
** Document
*/

Document::Document(QWidget *parent)
: QWidget(parent), m_currentIndex(-1), m_mousePressIndex(-1), m_resizeHandlePressed(false)
{
m_undoStack = new QUndoStack(this);

setAutoFillBackground(true);
setBackgroundRole(QPalette::Base);

QPalette pal = palette();
pal.setBrush(QPalette::Base, QPixmap(":/icons/background.png"));
pal.setColor(QPalette::HighlightedText, Qt::red);
setPalette(pal);

}

@

andreyc

If you zoom in you will see that background.png is not a white block.
It has two blue borders.

@
pal.setBrush(QPalette::Base, QPixmap(":/icons/background.png"));
@
uses a function "QPalette::setBrush":http://qt-project.org/doc/qt-5/qpalette.html#setBrush with the following signature
@
void QPalette::setBrush(ColorRole role, const QBrush & brush)
@
It calls "QBrush::QBrush":http://qt-project.org/doc/qt-5/qbrush.html#QBrush-7 contructructor
@
QBrush::QBrush(const QPixmap & pixmap)
@
"Constructs a brush with a black color and a texture set to the given pixmap. The style is set to "Qt::TexturePattern":http://qt-project.org/doc/qt-5/qt.html#BrushStyle-enum."

EdOfTheMountain

Thank you Eddy and Andre.

I zoomed into the 20 pixel square background.png image and saw that you are correct. There is a one pixel blue border on both right and bottom sides. I did not expect a grid to be implemented using an image like this.

I bet there are many useful background effects that could be accomplished using this technique. Thank you both for enlightening me.

-Ed