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generate the "un-pressed" image first, and then reload the image into your bitmap editor and make the changes manually. (I usually prefer to do this while Zoomed into the image so that I have a better view of the pixels themselves.) Figure 2 shows the two images generated by this process. The text in the second button has been moved up, and that the shadow underneath the arrow has been moved down and to the right. When these two images are set up in a screen, you'll see that the shadow in the pressed button moves, but so does the rest of the image. This is because FoxPro moves the whole image down and to the right by a single pixel. This needs to be countered. Adjusting the position of the second image Moving the second image up and to the left by one pixel corrects the look of the button. The arrow and "OK" text stay in their original position, but the shadow will move down and to the right by two pixels. Figure 3 shows the two final images. Allow for white space if necessary In bitmaps, white represents the background. When FoxPro sees white in the bitmap, it turns it into whatever color required for the button background, gray for the "un-pressed" button and light gray for the pressed button. This becomes obvious if you have gray as the background of the button image (try some of the sample buttons that Microsoft ships with FoxPro for Windows). You can display the color white on your buttons, but the method isn't obvious. If, for example, you want to mimic the appearance of the Windows 3.x Information message box, you will want to have a white exclamation point inside a blue circle. Typically, this would be drawn as shown in Figure 4. As you might have guessed, the problem with this is that the exclamation point will be the same color as the background behind the button: gray in the un-pressed button and light gray in the pressed button. You can override this default appearance by creating a "mask" of the image. A mask is a .BMP file that has the same filename as the original image, but with .MSK as the extension. Of course, the easiest way to create this is to define the bitmap that you want first, then copy it to a file with the .MSK extension (see Figure 5). The mask file contains only two colors: black and white. Wherever the color is black, the image itself shows through. Where the mask is white and the image is white, the background of the button shows through, and where the mask is white and the image is anything other than white, it seems like a negative of the image shows through. Table 1 shows this a bit more clearly. Table 1. Mask file vs. the image. White areas of .BMP Non-white areas of .BMP White portion of .MSK file Button Background Negative of the .BMP color
Black portion of .MSK file White The .BMP Color Conclusion The FoxPro manual shows most of the commands and functions that you can use along with some straightforward examples. What the manual can't show you is what you can do with this information. Whenever I see constructive, inventive interface and reporting requirements, I try to figure out what the author did to get that effect. Frequently, as with both of the examples here, the answer was staring me in the face in the manual. RTFM (Remember The "Fantastic" Manual), because it can frequently solve an elusive problem. The manual might not be the easiest or the best place to look for an answer, but it should be the first place that you look. Paul Russell, a software specialist with Software Kinetics Ltd., is chairman of the Fox Users of Nova Scotia, and is an active member of the FoxPro sections on the Internet. He has been programming for more than 10 years, with more than seven of those years of experience with the Fox product line. Internet prussell@fox.nstn.ca, or russell@atl.sofkin.ca, CompuServe 102440,2125. Subclassing Visual FoxPro Base Classes Richard A. Schummer (2) To subclass or not to subclass, that's the question. When, if ever, should you use Visual FoxPro base classes directly in your applications? At DevCon 95 and during the Visual FoxPro beta, the conventional wisdom was that developers should subclass all of Visual FoxPro's base classes. I went with the crowd at first, but then I changed course and used the Visual FoxPro-provided base classes directly. This article is about a bad decision and a learning experience that I want to pass along to the readers of this fine publication. I debated this process all during the beta and finally saw the light I was looking for. The basics Visual FoxPro comes with 29 base classes. These internally defined classes are provided by Microsoft and can't be modified directly. You can use these classes directly within an application, and you can subclass them. The conventional wisdom in the FoxPro community is that the base classes shouldn't be used directly in your applications. Instead, each should be subclassed, and you should use those subclasses (and other subclasses derived from them) in your applications (see Table 1). This will allow you to customize and standardize each class to have the functionality, look, and feel that you prefer. All the changes made to the subclassed
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