"Not so basic" drawing application

[lgeyer]

Well, a QPen consists of a QBrush consists of a QPixmap.

[Guest]

Yes, but it works nowhere near the way I need it to. Here is what it looks like:
!http://i42.tinypic.com/xd9nup.png(wrong)!

I don't need to fill the "volume" of the line with a pattern of the QBrush, I need to paint by dragging the brush for every pixel of the line. Notice the subtle difference? :)
!http://i44.tinypic.com/35a1w5t.png(right)!

[Eddy]

Have you looked at the scribble example?

[Guest]

Yes, it only uses an outline pen, it will work for the image posted above but it wont work for something like this:

!http://i41.tinypic.com/34hcewg.png(pixmap)!

The whole point is to not be restricted to a plain line (like scribble example is) but be able to paint by dragging the stencil you want to draw with.

Here is what scribble draws with:

@painter.setPen(QPen(myPenColor, myPenWidth, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin));
painter.drawLine(lastPoint, endPoint);@

And in fact, my very first post states that I failed to find what I need in the examples ;)

[andre]

Looks like this code will do exactly what you just showed above in your second example, and that you showed as an example of what you wanted...

[Guest]

There seems to be a form of miscommunication here, so lets go through everything step by step.

1 - this is my "brush" or stencil:
!http://i41.tinypic.com/34dr5nt.png(stencil)!

2 - this is what happens when I put the brush inside a QPixmap, which I put inside a QBrush, which I put inside a QPen
!http://i41.tinypic.com/21mde8j.png(wrong)!

The line is simply filled with a tiled pattern of the stencil
and the code for all of this:
@ QPainter painter(this);
QPixmap brush("c:/brush.png");
QBrush myBrush(Qt::red, brush);
QPen myPen;
myPen.setWidth(50);
myPen.setBrush(myBrush);
painter.setPen(myPen);
painter.drawLine(10, 10, 200, 50);@

note that I use the same method as in the scribble example, BUT this method only works for either solid or dashed lines, not for the stencil

3 - here is what dragging the stencil to draw should actually result it:
!http://i39.tinypic.com/2642m2e.png(right)!

drawLine can only draw strokes, not fills, strokes can only be solid or dashed but not pixmap, when a brush is set to a pen it tiles to fill the line, does not actually drag to draw it.

From DOC:

bq. The brush is used to fill strokes generated with the pen.

I don't need to fill the stroke with the brush, I need to DRAW it with the brush.
Is there a method to achieve the desired result?

[andre]

Wouldn't it as simple as interpolating between the two points, and simply blitting the stencil at every point in between? Just guessing here...

[Guest]

That was what I suggested many posts back as an alternative, in case there is no QPainter method to do that. It's just that you guys kept on insisting there is ;)

[Jake007]

Or you can use GIMP ;) .

Please mark thread as solved if you found the solution.

[Guest]

^^ And how exactly is your post helpful? From the many images I posted you should have concluded I already have a commercial image editor. And how exactly will GIMP help me to draw lines with stencils in my application? And thanks for your suggestion but I have plenty more questions on this topic, but those will have to wait till tomorrow. Geez... hunt rank much?

Anyway, I was able to do it with interpolation, the following is an actual screenshot, but it is a primitive, quick and dirty way to interpolate, and it shows - the lines are quite jagged, nowhere nearly as smooth as those in the images above, which I made in photoshop, will have to do some optimization tomorrow.
!http://i39.tinypic.com/2ntabgm.png(final)!

[andre]

Perhaps you can study how Krita works? From wat I read in the past, it is quite advanced in terms of brush handling.

[Guest]

Reinventing the wheel is usually a bad idea, but looking at the source code for Krita all I find is method calls within method calls within method calls, never really reaching the actual drawing logic. The project is so vast it will probably take me less time to reinvent the wheel in that particular case...

Perhaps if someone here is familiar with the project can give me a few pointers on where to look...

As for reinventing the wheel, I do realize I am stepping out of Qt land into generic algorithms so I will take it elsewhere.

[Guest]

BTW, here is my interpolation logic, it is fairly primitive, but I ain't no programmer yet, and I do realize Qt might have a better API for this, so any recommendations are welcome!

@void Widget::drawLine()
{
QPointF point, drawPoint;
point = newPos - lastPos;
int length = point.manhattanLength();
double xInc, yInc;

xInc = point.x() / length;
yInc = point.y() / length;

drawPoint = lastPos;

for (int x=0; x < length; ++x) {
    drawPoint.setX(drawPoint.x()+xInc);
    drawPoint.setY(drawPoint.y()+yInc);
    drawToCanvas(drawPoint);
}

}@

Edit: One optimization that comes to mind looking at the code now is use the rx and ry methods of QPoint that return references to use the += on and save the extra function call...