Create a Sudoku Puzzle Generator using VB.NET - Printing Puzzles
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While developing the generator, I couldn’t think of an easy and succinct way to print the puzzle. I toyed with simulating a printable grid using ASCII line characters, Excel and various third-party tools, but each potential solution fell short of what I envisioned, even introducing needless complexity. This feature almost remained on the enhancement list until I thought about an old program I wrote back in the VB3 days that facilitated screen captures.
The idea of presenting a printable, WYSIWYG rendition of the puzzle to the user was appealing, but I didn’t have the old code and writing it from scratch was not an option, especially for an optional feature. So it was as good a time as any to “borrow” some code. My web search led me to the Developerfusion UK website and an article written by James Crowley entitled "Capture a Screen Shot". You can find the article and code at http://www.developerfusion.co.uk/show/4630/. I ported a portion of the original C# code to VB and you’ll find it in the cScreenCapture class. Due to constraints on this article’s length, I’ll defer study of its logic to you.
The CaptureWindow()method is tasked with getting a snap shot of any window given its handle. As you might expect, the call to it is encapsulated in the cSudokuBoard class’ Print()method. The File > Print menu’s Click Event handler passes the handle of the panel control (containing the numeric labels that comprise the 9x9 cell puzzle grid) to the method and it returns a bitmap rendition of the puzzle. To scale and print the returned screen shot, the PrintDocument object and PrintPreviewDialog dialog box are employed. The PrintDocument defines “a reusable object that sends output to a printer” while the PrintPreviewDialog dialog box allows us to preview the output before sending it to the printer. By hooking a handler into the PrintDocument’s PrintPage event and assigning the document to the Document property of the dialog, we can actually render our bitmap onto the PrintDocument. The call to the ShowDialog method sets this all in motion, raising the PrintPage event handler, PrintPuzzleBoard() shown in Listing 5. The routine literally owner-draws the puzzle bitmap and some text onto the canvas of the PrintDocument and displays the document for preview (See Figure 4) and eventual printing.
Listing 5 Render the puzzle onto the print preview document
Private Sub PrintPuzzleBoard(ByVal sender As Object, _
ByVal e As System.Drawing.Printing.PrintPageEventArgs) e System.Drawing.Printing.PrintPageEventArgs)
'This subroutine sinks the PrintPage event raised by the PrintDialog.
'It draws header and footer information and the captured puzzle bitmap unto the
'graphics canvas of the PrintDocument.
'
'Use GDI+ to scale the image for printing
With e.Graphics
'Make sure to draw the puzzle image within the bounds of the printed page's margins
'Image is scaled and centered automatically
.DrawImage(mbmp_PuzzleBoardImage, e.MarginBounds)
.DrawString(msb_PuzzlePrintHeader.ToString & me_SelectedComplexity.ToString, _
New Font("MS Trebuchet", 20, FontStyle.Bold), Brushes.Blue, _
e.MarginBounds.X, e.PageBounds.Y + 50)
.DrawString(msb_PuzzlePrintFooter.ToString, New Font("MS Trebuchet", 10, _
FontStyle.Bold), Brushes.Blue, e.MarginBounds.X, _
e.MarginBounds.Bottom + 5)
End With
e.HasMorePages = False
End Sub
Figure 4. The Puzzle Print Preview
Enhancing the Puzzle Generator
During the design phase, I came up with various ideas for improving the generator, but alas there are only so many hours in a day and I could not implement them all. Following are some of the better enhancement ideas you may wish to incorporate. Drop me an email if you do get around to implementing any or if you come up with a great one yourself!
1. Include some AI to generate challenging puzzles.
2. Create a user-drawn Graphical User Interface (GUI).
3. Support multiple solutions for puzzles of greater complexity.
4. Create a timed version of the puzzle.
5. Substitute colors, shapes, or text for the numbers.
In general, I find that nothing exercises a computer’s capabilities better than the development of a great puzzle, strategy, or arcade game. It’s not only an entertaining endeavor, but a rich learning experience. Hopefully you have come away with a better understanding of Sudoku and the different techniques used to provide its features. Maybe the next time you won’t be in such a hurry to buy or download the latest must-have game and instead you’ll challenge yourself to program it. Hope you enjoyed this as much as I did. Happy Programming and Gaming!
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