Welcome to the CSIG, a Special Interest Group of the ACGNJ. The subject for this month is short journey into C++ Graphical Windows programming. In addition, mathematical and trigonometric functions will be discussed.

Let's build a clock using Windows Graphics. We could ask the system for the time and print the values to the screen in a large font but that's not very challenging. How about an analog clock: one with hands. How do the hands move? There are 43,200 seconds in a 12 hour rotation of a clock. This means that the hour hand moves 360 degrees in that many seconds. In order to design a program to move the hour hand every second, it would have to move 0.00833333333 degrees each time. Can this be done in C++ ? Sure. How about the minute hand. There are 3600 seconds in a 1 hour rotation.. This means that the minute hand moves 360 degrees in that many seconds. For each second it would have to move 0.1000 degrees. As you can see, there's a little bit of math involved. There's also trigonometry which we'll discuss at the meeting.

void TimePiece::show_time(void) /* display the clock */ { static struct DEGREES last_deg, deg; static int firstime = 1; current.hr = current.hr % 12; deg.hr = (double)current.hr*30.0 + (double)current.min/2.0 + (double)(current.sec & 0xFF)/120.0; deg.min = (double)current.min*6.0 + (double)(current.sec & 0xFF)/10.0; // was FE deg.sec = (double)current.sec*6.0; hand(0.50, deg.hr); /* hour hand */ hand(0.75, deg.min); /* minite hand */ pivot(0.05); } void TimePiece::pivot(double radius) /* draw pivot */ { int x1, y1, x2, y2; x1 = (int)((-radius)*1000); y1 = (int)((-radius)*1000); x2 = (int)((+radius)*1000); y2 = (int)((+radius)*1000); pdc->Ellipse(x1, y1, x2, y2); } void TimePiece::hand(double size, double angle) /* draw hand */ { struct FPOINT p3, center; oldPen = (HPEN)pdc->SelectObject(mPen); oldBrush = (HBRUSH)pdc->SelectObject(mBrush); /* P3 */ center.wx = center.wy = 0.0; /* | */ p3.wx = size * sin( angle*2.0*PI/360.0); /* | */ p3.wy = size * cos( angle*2.0*PI/360.0); /* | */ /* CENTER */ line(center, p3); pdc->SelectObject(oldPen); pdc->SelectObject(oldBrush); } void TimePiece::line(struct FPOINT p1, struct FPOINT p2) /* draw line */ { int x, y; x = (int)(p1.wx * 1000); y = (int)(p1.wy * 1000); pdc->MoveTo(x, y); x = (int)(p2.wx * 1000); y = (int)(p2.wy * 1000); pdc->LineTo(x, y); } void TimePiece::face(void) /* add circles for hour marks */ { struct FPOINT p1; int x1, y1, x2, y2, i; double deg, dot_radius, ul_x, ul_y, lr_x, lr_y; for (dot_radius=0.09,i=0; i<1; i += 1) // for 12 hours change to "i<12" { deg = (double)i*30.0; p1.wx = 0.85*sin( deg*2.0*PI/360.0); // = 0.000 at 12:00 o'clock p1.wy = 0.85*cos( deg*2.0*PI/360.0); // = 0.850 ul_x = p1.wx-dot_radius; ul_y = p1.wy+dot_radius; lr_x = p1.wx+dot_radius; lr_y = p1.wy-dot_radius; x1 = (int)(ul_x*1000); y1 = (int)(ul_y*1000); x2 = (int)(lr_x*1000); y2 = (int)(lr_y*1000); pdc->Ellipse(x1, y1, x2, y2); } }

"Random Access" questions start at 7:30 Tuesday night.

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