Specifying Windows "Bounding Box" Coordinates

 Last reviewed: November 2, 1995
Article ID: Q27585
The information in this article applies to:
  • Microsoft Windows Software Development Kit (SDK) for Windows versions 3.1 and 3.0
  • Microsoft Win32 Application Programming Interface (API) included with: 

        - Microsoft Windows NT versions 3.5 and 3.51
    - Microsoft Windows 95 version 4.0

SUMMARY

GDI functions, such as Rectangle, Ellipse, RoundRect, Chord, and Pie, have parameters that specify the coordinates of a "bounding box" into which the figure is drawn. Windows draws the figure up to, but not including, the right and bottom coordinates.

MORE INFORMATION

Suppose the following call is made: 

   Rectangle(hDC, 1, 1, 5, 3)
Assuming that the device context is using the MM_TEXT mapping mode (in which case logical units map directly to physical pixels), the resulting rectangle will be 4 pixels wide and 2 pixels tall. The following diagram shows which pixels are affected: 

            ---0-----1-----2-----3-----4-----5-----6-
            |     |     |     |     |     |     |
            0     |     |     |     |     |     |
            |-----|-----|-----|-----|-----|-----|----
            |     |     |     |     |     |     |
            1     |  X  |  X  |  X  |  X  |     |
            |-----|-----|-----|-----|-----|-----|----
            |     |     |     |     |     |     |
            2     |  X  |  X  |  X  |  X  |     |
            |-----|-----|-----|-----|-----|-----|----
            |     |     |     |     |     |     |
            3     |     |     |     |     |     |
            |-----|-----|-----|-----|-----|-----|----
            |     |     |     |     |     |     |
            4     |     |     |     |     |     |
It may be helpful to think of the display as a grid, with each pixel contained in a grid cell. The X1, Y1, X2, and Y2 parameters to the Rectangle function specify an imaginary "bounding box" drawn on the grid. The rectangle is drawn within the bounding box.

The height, width, and area of the resulting rectangle have the following useful properties: 

   Height = X2 - X1
   Width  = Y2 - Y1
   Area   = Height * Width

Additional reference words: 3.00 3.10 3.50 4.00 95
KBCategory: kbgraphic
KBSubcategory: GdiDrw

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Last reviewed: November 2, 1995
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