![[SEAV Softwares Logo]](../gfx/w_cologo.gif) |
  |
|
        |
Sure, you know how to display time using TIME$, but do you know how to draw a real-time analog clock? (You know the one with the hour hand, the minute hand, and the second hand?) Let's see if you can do it. Use screen mode 12. Make it fancy if you want. Download the B3 Zip file containing this page plus QBASIC files for you to try. Go back to the Case Study page. |
||||
|
|
||||||||
 |
It's very simple. If you're going to think about it, our problem is just a matter of converting the actual time to the angles that measure the rotation of the hour, the minute, and the second hand. The hour hand makes a complete revolution every 12 hours, the minute hand every hour, and the second hand every minute. Thus, we need a function to find the angles of the three hands given the time. Once we have the angles, we can use trigonometry to draw the hands. We can draw simple hands or complex hands—anything we want as long as we have the angles. Getting the hour, the minute, and the second. I know of two simple ways to get the hour, the minute, and the second, each in its own variable. One is to extract the data from the string returned by TIME$:
The other technique is by using TIMER:
Take note that the variable I used to copy the value of TIMER is in Long Integer format (instead of just Integer). Find the reason why? Now you know how to
extract those things. But that is not what we want. (Haha.) We still need
the fractional parts of their value. Why? If we just got the integral parts,
the clock hands will point at discrete directions. What I mean is, if the
time is 4:30, the hour hand will point at four, instead of between four and
five. See what I mean? So the correct code should be:
Here, we made the second value an integer value. If you want it to have fractional values so that the second hand will move continuously instead of jumping every second, you can do so. The reason why I made it that way is so that we just have to update the clock display every second, instead of continuously (which could be flickery). I've noticed that
there's no easy way to get the value for the minutes. I just made it so
that I extract the integer value and then I just add the fraction of the
minute depending on the second value.By the way, you may
notice that we reduced the hour value to 12-hour format instead of the
usual 24-hour format since the hour hand makes a complete revolution every
12 hours (actually, it won't really matter in some applications, but we
might use a specific range of angles through look-up tables and such...).Converting to the angles. Now that we have the time values in their respective variables, we can now find the angles corresponding to each value. For convenience, we'll redefine the angular system so that 0° points up, to the 12 o'clock position, and the angle values increase in the clockwise direction. So 90° points to the 3 o'clock position, 180° points at 6 o'clock, and so on. I said that the screen
mode we should use is SCREEN 12. Well, I plan on not changing the screen
coordinate system, which is just like the Cartesian Coordinate System
flipped along the x-axis (i.e., the positive x direction goes to the right
and the positive y direction goes downwards). And I plan on using the
trigonometric functions to convert the angle to the appropriate rectangular
coordinates. So my x-coordinate function would be sine (with respect
to my choice of angular system) and my y-coordinate function would be
negative cosine. Figure out why.With those things out
of the way, let's now proceed with the time-value-to-angle functions. By
simple computation, we find out that the hour hand moves 30° every
hour, while the minute and second hands both move 6° every minute
and every second respectively. So we just multiply their corresponding
unit interval angle with their values. We also convert the angles to
radians since we'll be using the trig functions.
Voila! Now we're through getting the angles! Displaying the clock. The next process is to display the clock. What I'm going to do here is to show a very simple display. The clock would be centered on the screen. It's border will be a circle with a radius of 200 pixels. The hands will just be lines radiating from the center, with the hour hand having a length of 120 pixels, the minute hand 180 pixels, and the second hand 190 pixels. Our center pixel is (320, 240). To make sure that we
update the the clock every second instead of continuously, we just do a
looping check for the integral value of TIMER
and redraw the clock whenever the value changes.
Here is code to draw the hands given the angles:
Why we still put the coordinates in their own variables will be apparent when we update the clock. Before, we can update the clock, we need to erase the hands first and it would be faster to erase the hands by redrawing over them with the background color instead of doing a CLS. Here's the complete
program with all the parts added and combined:
Here's a sample output: I took this screenshot at around 10:15 pm.A little bit of fancy. That clock display looks very boring. Lets spice it up a little by adding second tick marks on the border and by extending the hands in the other direction by 30 pixels. Here's the revised code (I've highlighted the changes):
Here's the output to that program. The modifications I made to the program
deal with drawing the second tick marks around the border and the addition
of six new variables to track the position of the other endpoint of every
hand. Looks better, doesn't it? |
||||||||
|
|||||||||
|
|
Try creating more fancier clock displays! If you'll download the B3 Zip file, you'd find the previous two programs plus one more program showing the possibilities. |
||||||||
|
Go back to the Case Study page. Home Page | Program Nook | Instructional | Open Forum Portfolio | Visitor's Area | Connections | About the Site Copyright © 1997-1999, SEAV Softwares. All rights reserved. Webmaster: Eugene Villar (SEAV); e-mail: evillar@iname.com |