Vista - Drawing Line on Canvas

All:

OK - I know this seems like a ridiculously simply question, but I
cannot find an answer. In the "old days" of Windows programming (the
old days include .NET 2.0 Forms), one could somehow obtain a graphics
context, e.g., CreateGraphics() and draw on a form, etc.

How do you do the same thing in WPF (Windows Presentation Foundation)?
I am simply trying to draw (render) a line on a Canvas - that's it.

There does seem to be an equivalent of CreateGraphics() or GetDC() or
GetDrawingContext() - or anything one would naturally assume to be
present in an API of this type.

Examples?

Thank you,
jpuopolo

In article <1162607686.882875.230630@m7g2000cwm.googlegroups.com>,
puopolo@gmail.com says...
> All:
>
> OK - I know this seems like a ridiculously simply question, but I
> cannot find an answer. In the "old days" of Windows programming (the
> old days include .NET 2.0 Forms), one could somehow obtain a graphics
> context, e.g., CreateGraphics() and draw on a form, etc.
>
> How do you do the same thing in WPF (Windows Presentation Foundation)?
> I am simply trying to draw (render) a line on a Canvas - that's it.
>
> There does seem to be an equivalent of CreateGraphics() or GetDC() or
> GetDrawingContext() - or anything one would naturally assume to be
> present in an API of this type.
>
> Examples?
>
> Thank you,
> jpuopolo
>
>

Have a look at the SDK Documentation
(http://windowssdk.msdn.microsoft.com/en-
us/library/system.windows.media.drawingcontext.aspx) for the
DrawingContext class, especially the remarks which explain (in addition
to its differences with the old school device context):

"When you use a DrawingContext object's draw commands, you are actually
storing a set of rendering instructions (although the exact storage
mechanism depends on the type of object that supplies the
DrawingContext) that will later be used by the graphics system; you are
not drawing to the screen in real-time."
----
for just basic "line on a canvas...
From the SDK Documentation's "How to: Draw a Line"...

<Canvas Height="300" Width="300">

<!-- Draws a diagonal line from (10,10) to (50,50). -->
<Line
X1="10" Y1="10"
X2="50" Y2="50"
Stroke="Black"
StrokeThickness="4" />

<!-- Draws a diagonal line from (10,10) to (50,50)
and moves it 100 pixels to the right. -->
<Line
X1="10" Y1="10"
X2="50" Y2="50"
StrokeThickness="4"
Canvas.Left="100">
<Line.Stroke>
<RadialGradientBrush GradientOrigin="0.5,0.5" Center="0.5,0.5"
RadiusX="0.5" RadiusY="0.5">
<RadialGradientBrush.GradientStops>
<GradientStop Color="Red" Offset="0" />
<GradientStop Color="Blue" Offset="0.25" />
</RadialGradientBrush.GradientStops>
</RadialGradientBrush>
</Line.Stroke>
</Line>

<!-- Draws a horizontal line from (10,60) to (150,60). -->
<Line
X1="10" Y1="60"
X2="150" Y2="60"
Stroke="Black"
StrokeThickness="4"/>

</Canvas>

------------

// Add a Line Element
myLine = new Line();
myLine.Stroke = Brushes.LightSteelBlue;
myLine.X1 = 1;
myLine.X2 = 50;
myLine.Y1 = 1;
myLine.Y2 = 50;
myLine.HorizontalAlignment = HorizontalAlignment.Left;
myLine.VerticalAlignment = VerticalAlignment.Center;
myLine.StrokeThickness = 2;
myGrid.Children.Add(myLine);

-----------

Bob:

Thanks - works like a charm.

Best,
John

Bob wrote:
> In article <1162607686.882875.230630@m7g2000cwm.googlegroups.com>,
> puopolo@gmail.com says...
> > All:
> >
> > OK - I know this seems like a ridiculously simply question, but I
> > cannot find an answer. In the "old days" of Windows programming (the
> > old days include .NET 2.0 Forms), one could somehow obtain a graphics
> > context, e.g., CreateGraphics() and draw on a form, etc.
> >
> > How do you do the same thing in WPF (Windows Presentation Foundation)?
> > I am simply trying to draw (render) a line on a Canvas - that's it.
> >
> > There does seem to be an equivalent of CreateGraphics() or GetDC() or
> > GetDrawingContext() - or anything one would naturally assume to be
> > present in an API of this type.
> >
> > Examples?
> >
> > Thank you,
> > jpuopolo
> >
> >
>
> Have a look at the SDK Documentation
> (http://windowssdk.msdn.microsoft.com/en-
> us/library/system.windows.media.drawingcontext.aspx) for the
> DrawingContext class, especially the remarks which explain (in addition
> to its differences with the old school device context):
>
> "When you use a DrawingContext object's draw commands, you are actually
> storing a set of rendering instructions (although the exact storage
> mechanism depends on the type of object that supplies the
> DrawingContext) that will later be used by the graphics system; you are
> not drawing to the screen in real-time."
> ----
> for just basic "line on a canvas...
> From the SDK Documentation's "How to: Draw a Line"...
>
> <Canvas Height="300" Width="300">
>
> <!-- Draws a diagonal line from (10,10) to (50,50). -->
> <Line
> X1="10" Y1="10"
> X2="50" Y2="50"
> Stroke="Black"
> StrokeThickness="4" />
>
> <!-- Draws a diagonal line from (10,10) to (50,50)
> and moves it 100 pixels to the right. -->
> <Line
> X1="10" Y1="10"
> X2="50" Y2="50"
> StrokeThickness="4"
> Canvas.Left="100">
> <Line.Stroke>
> <RadialGradientBrush GradientOrigin="0.5,0.5" Center="0.5,0.5"
> RadiusX="0.5" RadiusY="0.5">
> <RadialGradientBrush.GradientStops>
> <GradientStop Color="Red" Offset="0" />
> <GradientStop Color="Blue" Offset="0.25" />
> </RadialGradientBrush.GradientStops>
> </RadialGradientBrush>
> </Line.Stroke>
> </Line>
>
> <!-- Draws a horizontal line from (10,60) to (150,60). -->
> <Line
> X1="10" Y1="60"
> X2="150" Y2="60"
> Stroke="Black"
> StrokeThickness="4"/>
>
> </Canvas>
>
> ------------
>
> // Add a Line Element
> myLine = new Line();
> myLine.Stroke = Brushes.LightSteelBlue;
> myLine.X1 = 1;
> myLine.X2 = 50;
> myLine.Y1 = 1;
> myLine.Y2 = 50;
> myLine.HorizontalAlignment = HorizontalAlignment.Left;
> myLine.VerticalAlignment = VerticalAlignment.Center;
> myLine.StrokeThickness = 2;
> myGrid.Children.Add(myLine);
>
> -----------

Old-world-style, you can also override OnRender. Looks like old-world DC
rendering, feels like old-world DC rendering, but it isn't. And it works
perfectly well. You can mix-and-match xaml and OnRender rendering as well.

My feeling: xaml is great, but sooner or later you'll need to render to a DC
directly.

> "john" wrote:

> Bob:
>
> Thanks - works like a charm.
>
> Best,
> John
>
> Bob wrote:
> > In article <1162607686.882875.230630@m7g2000cwm.googlegroups.com>,
> > puopolo@gmail.com says...
> > > All:
> > >
> > > OK - I know this seems like a ridiculously simply question, but I
> > > cannot find an answer. In the "old days" of Windows programming (the
> > > old days include .NET 2.0 Forms), one could somehow obtain a graphics
> > > context, e.g., CreateGraphics() and draw on a form, etc.
> > >
> > > How do you do the same thing in WPF (Windows Presentation Foundation)?
> > > I am simply trying to draw (render) a line on a Canvas - that's it.
> > >
> > > There does seem to be an equivalent of CreateGraphics() or GetDC() or
> > > GetDrawingContext() - or anything one would naturally assume to be
> > > present in an API of this type.
> > >
> > > Examples?
> > >
> > > Thank you,
> > > jpuopolo
> > >
> > >
> >
> > Have a look at the SDK Documentation
> > (http://windowssdk.msdn.microsoft.com/en-
> > us/library/system.windows.media.drawingcontext.aspx) for the
> > DrawingContext class, especially the remarks which explain (in addition
> > to its differences with the old school device context):
> >
> > "When you use a DrawingContext object's draw commands, you are actually
> > storing a set of rendering instructions (although the exact storage
> > mechanism depends on the type of object that supplies the
> > DrawingContext) that will later be used by the graphics system; you are
> > not drawing to the screen in real-time."
> > ----
> > for just basic "line on a canvas...
> > From the SDK Documentation's "How to: Draw a Line"...
> >
> > <Canvas Height="300" Width="300">
> >
> > <!-- Draws a diagonal line from (10,10) to (50,50). -->
> > <Line
> > X1="10" Y1="10"
> > X2="50" Y2="50"
> > Stroke="Black"
> > StrokeThickness="4" />
> >
> > <!-- Draws a diagonal line from (10,10) to (50,50)
> > and moves it 100 pixels to the right. -->
> > <Line
> > X1="10" Y1="10"
> > X2="50" Y2="50"
> > StrokeThickness="4"
> > Canvas.Left="100">
> > <Line.Stroke>
> > <RadialGradientBrush GradientOrigin="0.5,0.5" Center="0.5,0.5"
> > RadiusX="0.5" RadiusY="0.5">
> > <RadialGradientBrush.GradientStops>
> > <GradientStop Color="Red" Offset="0" />
> > <GradientStop Color="Blue" Offset="0.25" />
> > </RadialGradientBrush.GradientStops>
> > </RadialGradientBrush>
> > </Line.Stroke>
> > </Line>
> >
> > <!-- Draws a horizontal line from (10,60) to (150,60). -->
> > <Line
> > X1="10" Y1="60"
> > X2="150" Y2="60"
> > Stroke="Black"
> > StrokeThickness="4"/>
> >
> > </Canvas>
> >
> > ------------
> >
> > // Add a Line Element
> > myLine = new Line();
> > myLine.Stroke = Brushes.LightSteelBlue;
> > myLine.X1 = 1;
> > myLine.X2 = 50;
> > myLine.Y1 = 1;
> > myLine.Y2 = 50;
> > myLine.HorizontalAlignment = HorizontalAlignment.Left;
> > myLine.VerticalAlignment = VerticalAlignment.Center;
> > myLine.StrokeThickness = 2;
> > myGrid.Children.Add(myLine);
> >
> > -----------
>
>