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VB 6 Helper Newsletter
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Rod Stephens
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May 07, 2009 07:03 PDT
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My book "Beginning Database Design Solutions" got two new, very positive
reviews at Amazon. Check 'em out at:
http://www.amazon.com/Beginning-Database-Design-Solutions-Programmer/product-reviews/0470385499/ref=dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1
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DevX posted another of my WPF articles:
WPF Wonders: An Alphabetical Compendium of WPF Controls
http://www.devx.com/dotnet/Article/41560
Among many other changes, WPF brings a completely new set of
controls. Learn which controls do what and pick up a few tips on getting
the most out of them in your WPF applications.
This article summarizes the most useful WPF controls. Some will be
familiar friends (TextBox, Label, Button) but others will be new
acquaintances (StackPanel, BulletDecorator, DocumentViewer).
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I've just posted an XAML-only robot arm example. It's pretty cool both
because of what it does and because it uses absolutely no code (other
than XAML code) to control three joints and a hand.
I'm not sure how much farther you could take this article and get
something actually useful out of it but it's impressive that you can get
this far without writing code.
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Have a great week and thanks for subscribing!
Rod
RodSte-@vb-helper.com
Books To Keep: http://www.BooksToKeep.com
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*** Now Available ***
Beginning Database Design Solutions
http://www.amazon.com/exec/obidos/ASIN/0470385499/vbhelper/
Visual Basic 2008 Programmer's Reference
http://www.amazon.com/exec/obidos/ASIN/0470182628/vbhelper/
==========
Both Contents:
1. New HowTo: Simulate a robot arm with three rotating joints and a hand
using XAML code
==========
++++++++++
<Both>
++++++++++
==========
1. New HowTo: Simulate a robot arm with three rotating joints and a hand
using XAML code
http://www.vb-helper.com/howto_xaml_robot_arm.html
http://www.vb-helper.com/HowTo/howto_xaml_robot_arm.zip
(Picture at http://www.vb-helper.com/howto_xaml_robot_arm.jpg.)
The basic idea is to consider the stages of the arm one after another
and use transformations to move from one to the next.
Suppose the three arm segments have lengths L1, L2, and L3 and the
angles of rotation at the three joints are A1, A2, and A3.
The first joint rotates the arm by angle A1 at a fixed shoulder. The
second joint is translated distance L1 away in the direction of the
first arm segment.
The second joint rotates the arm by angle A2 at the "elbow." The third
joint is translated distance L2 away in the direction of the second arm
segment.
The third joint rotates the arm by angle A3 at the "wrist." The end of
the arm is translated distance L3 away in the direction of the third arm
segment.
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To draw the arm, start by drawing the shoulder at the origin. This
example adds a translation first to center the shoulder in the drawing
area.
Next the code applies the rotation A1 at the shoulder and draws a
rectangle representing the first arm segment. There are is one tricky
issue here.
The rotation is <B>prepended</B> to the previous translation so the
rotation occurs before the translation that centers the shoulder.
Imagine the arm in its own world coordinate space with the shoulder at
the origin. The program draws a horizontal rectangle representing the
first arm segment. The transformations then rotate it to the correct
angle and translate it so the shoulder is centered. This puts the first
arm segment in the correct position.
Next the code must draw the elbow joint. To do this, it <B>prepends</B>
a translation of distance L1 in the X direction and 0 in the Y
direction. It then draws the elbow joint at the origin.
Again imagine the arm in world coordinate space and suppose you draw the
elbow at the origin. The new translation moves the joint to (L1, 0). The
rotation of angle A1 rotates the joint to match the rotation of the
first arm segment. Finally the shoulder's translation moves the whole
thing so the base of the first arm segment is centered in the drawing
area.
The code continues like this as many times as necessary to draw each arm
segment and joint. In eachv step, it prepends the new translations and
rotations.
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The following code shows how the program draws the third arm segment.
Notice how is uses binding to use the angles selected by the slider
controls sliJoint1, sliJoint2, and sliJoint3. The values L1 and L2 are
static resource values giving the arm lengths. The values Cx and Cy give
the center of the drawing area.
<!-- Third arm segment -->
<Line X1="0" Y1="0" X2="{StaticResource L3}" Y2="0">
<Line.RenderTransform>
<TransformGroup>
<RotateTransform Angle="{Binding ElementName=sliJoint3,
Path=Value}"/>
<TranslateTransform X="{StaticResource L2}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint2,
Path=Value}"/>
<TranslateTransform X="{StaticResource L1}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint1,
Path=Value}"/>
<TranslateTransform X="{StaticResource Cx}" Y="{StaticResource
Cy}"/>
</TransformGroup>
</Line.RenderTransform>
</Line>
The code finishes by drawing a hand with two fingers. As it does for the
rest of the arm, the code draws the pieces of the hand at the origin and
uses transformations to move it where it belongs. The following code
shows how the program draws the hand. There are lots of details but the
only real tricks is how the program draws Finger 1. The sliHand slider
control determines how far apart the fingers are. The program uses its
value directly to draw Finger 2. To draw Finger 1, it uses a
ScaleTransform to reflect the translation across the X axis, making the
finger move the negative of the distances selected by sliHand.
<!-- Hand - Palm -->
<Line X1="0" Y1="-15" X2="0" Y2="15" Stroke="Black" StrokeThickness="3">
<Line.RenderTransform>
<TransformGroup>
<TranslateTransform X="{StaticResource L3}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint3,
Path=Value}"/>
<TranslateTransform X="{StaticResource L2}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint2,
Path=Value}"/>
<TranslateTransform X="{StaticResource L1}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint1,
Path=Value}"/>
<TranslateTransform X="{StaticResource Cx}" Y="{StaticResource
Cy}"/>
</TransformGroup>
</Line.RenderTransform>
</Line>
<!-- Hand - Finger 1 -->
<Line X1="0" Y1="0" X2="20" Y2="0" Stroke="Black" StrokeThickness="3">
<Line.RenderTransform>
<TransformGroup>
<TranslateTransform X="0" Y="{Binding ElementName=sliHand,
Path=Value}"/>
<ScaleTransform ScaleX="1" ScaleY="-1"/>
<TranslateTransform X="{StaticResource L3}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint3,
Path=Value}"/>
<TranslateTransform X="{StaticResource L2}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint2,
Path=Value}"/>
<TranslateTransform X="{StaticResource L1}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint1,
Path=Value}"/>
<TranslateTransform X="{StaticResource Cx}" Y="{StaticResource
Cy}"/>
</TransformGroup>
</Line.RenderTransform>
</Line>
<!-- Hand - Finger 2 -->
<Line X1="0" Y1="0" X2="20" Y2="0" Stroke="Black" StrokeThickness="3">
<Line.RenderTransform>
<TransformGroup>
<TranslateTransform X="0" Y="{Binding ElementName=sliHand,
Path=Value}"/>
<TranslateTransform X="{StaticResource L3}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint3,
Path=Value}"/>
<TranslateTransform X="{StaticResource L2}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint2,
Path=Value}"/>
<TranslateTransform X="{StaticResource L1}" Y="0"/>
<RotateTransform Angle="{Binding ElementName=sliJoint1,
Path=Value}"/>
<TranslateTransform X="{StaticResource Cx}" Y="{StaticResource
Cy}"/>
</TransformGroup>
</Line.RenderTransform>
</Line>
==========
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