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In the example eVB project you will
see that the MouseDown event has been modified to
store the Y coordinate + 128, this sets the MSB of the Y
byte signifying the start of a new line. Coordinates stored
in the MouseMove event do not set the MSB, and are
therefore interpreted as being line ends.
After capturing the coordinates into
an array using this method, we are ready to store the results.
Personally I like to see my data, so in the example project
I've encoded the data into a text string that can easily
be stored in a database record or even written out as XML.
The string is simply the coordinates pairs stored in 8-bit
hexadecimal format, no delimiting is necessary as each pair
will always consist of 4 characters.
E.g. "XXYYxxyyxxyyxxyyXXYYxxyyxxyy"
(Capitals denote MSB set in Y)
Example Projects
The example Pocket PC eVB project included
with this article is a simple demonstration form that you
can sign. The encoded results are then displayed as text
as well as being written to the file "\my documents\signature.txt".
One notable feature of the demo is the "Sign Here"
watermark effect in the signature box, since we aren't storing
the actual graphics you could use any image you like!
To demonstrate how simple decoding is,
also included with this article is a desktop PC Visual Basic
project that will load the signature file, decode it, and
display the results.
Final analysis
In case you're not quite convinced,
take a look at the following example and scale the savings
made over the number of signatures you expect to capture
during a working session.
| Raw image |
19,200 bytes |
| GIF image |
1,400 bytes |
| Text Vector |
508 bytes |
| Raw Vector |
254 bytes |
I’m sure most people would be quite
happy with the loss of compression due to storing the vector
in text format, simply because it is so much easier to handle.
Best of all though, it’s all been possible without
adding any extra controls!
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