WinApi LineTo not refreshing the line - c++

Question

I'm just starting learning C++. All I want to do is drawing a line to a specified coord, which comes as an input in a method. I set the starting point in each loop (calling this function in a loop with different arguments) using MoveToEx and giving the coordinates in which I want lane to be drawn.
Any ideas how to make it working in a loop?
My code is similar to:
void Clock::drawSecondLine(float x,float y) {
HWND console_handle = GetConsoleWindow();
HDC device_context = GetDC(console_handle);
HPEN pen = CreatePen(PS_SOLID, 3, RGB(255, 0, 0));
SelectObject(device_context, pen);
MoveToEx(device_context, 0, 0, NULL);
Ellipse(device_context, 400, 0, 0, 400);
MoveToEx(device_context, 200, 200, NULL);
LineTo(device_context, (int)x, (int)y);
ReleaseDC(console_handle, device_context);
cin.ignore();
}
And the loop:
void Zegar::startClock() {
while (true) {
drawSecondLine(laneShowingSecond.getX(), laneShowingSecond.getY());
laneShowingSecond.movePointByRadius(RADIUS_PER_SECOND);
Sleep(1000);
increaseSecond();
}
}

Answer 1

Here's some sample code (which I am running in VStudio 2k10).
Notes:
Although it is compiled as C++ (and uses some C++ features like iostream - meaning that it won't compile as C), it's still plain old C.
It has a lot of ugly stuff and NO-NO s (like global vars, lots defines, mixture of C and C++ code, drawing on the console window, ...). The goal was to have a PoC; the code can be cleansed later.
From the bounding rectangle (RECT_* defines (400, 0, 0, 400)) I am extracting the center coordinates, and the radii on the X and Y axes, using some simple mathematical calculations (due to the fact that the rectangle is a square, the 2 radii are equal so we hit the particular case where the ellipse is actually a circle).
nextPoint function is the replacement of laneShowingSecond.getX(), laneShowingSecond.getY() from your code.
Everything that needs to be only executed once (at the beginning) is placed in the init function. Note that if something goes wrong during initialization, it exits with an error (< 0) code, since it won't be able to draw.
Similarily, any cleanup stuff to be performed at the end is placed in the cleanup function (here I didn't bother to check for return codes since it's exiting anyway).
The draw function contains the drawing loop. In every iteration:
The angle is incremented by INCERMENT_DEG (which by default is 30°).
The next point on the ellipse is calculated using some simple trigonometrical formulas.
The drawing is performed.
A wait of ITERATION_SLEEP_TIME milliseconds (I've set it to 200 to avoid waiting one second for each line drawn) takes place.
Note that:
It stops after reaching 360° or 2 * PI Radians (round-the-clock), because it doesn't make sense to draw the same lines over and over again.
The drawing is performed counter-clockwise (positive angles in trigonometry); also the xOy origin (O(0, 0)) is screen's upper left corner.
Play with the defines that I marked with comments, by assigning various values to them and see how the drawing changes.
main.cpp:
#include <iostream>
#define _USE_MATH_DEFINES
#include <math.h>
#include <Windows.h>
#define RECT_LEFT 400 // Modify any of these 4 RECT_* values to get different ellipse shapes.
#define RECT_TOP 0
#define RECT_RIGHT 0
#define RECT_BOT 400
#define ITERATION_SLEEP_TIME 200 // Sleep time while in loop.
#define INCERMENT_DEG 30 // 30 degrees per step; a full circle has 360 (2 * PI RAD).
#define M_PI_180 M_PI / 180
using std::cout;
using std::endl;
typedef enum {DRAW_RADII, DRAW_POLY} DrawMethod;
const int radiusX = abs(RECT_RIGHT - RECT_LEFT) / 2;
const int radiusY = abs(RECT_BOT - RECT_TOP) / 2;
const int centerX = (RECT_RIGHT + RECT_LEFT) / 2;
const int centerY = (RECT_BOT + RECT_TOP) / 2;
HWND hwnd = NULL;
HDC hdc = NULL;
HPEN hpen = NULL;
DrawMethod meth = DRAW_RADII; // Modify this to DRAW_POLY to draw a polygon instead of the "bike wheel".
int deg = 0;
double x = 0, y = 0;
void nextPoint(int degree, double *x, double *y) {
*x = centerX + radiusX * cos(M_PI_180 * degree );
*y = centerY - radiusY * sin(M_PI_180 * degree);
}
int init() {
if ((hwnd = GetConsoleWindow()) == NULL) {
cout << "GetConsoleWindow error: " << GetLastError() << endl;
return -1;
}
if ((hdc = GetDC(hwnd)) == NULL) {
cout << "GetDC error: " << GetLastError() << endl;
return -2;
}
if ((hpen = CreatePen(PS_SOLID, 3, RGB(255, 0, 0))) == NULL) {
cout << "CreatePen error: " << GetLastError() << endl;
return -3;
}
SelectObject(hdc, hpen);
Ellipse(hdc, RECT_LEFT, RECT_TOP, RECT_RIGHT, RECT_BOT);
nextPoint(deg, &x, &y);
if (meth == DRAW_RADII) {
MoveToEx(hdc, centerX, centerY, NULL);
LineTo(hdc, (int)x, (int)y);
} else if (meth == DRAW_POLY) {
MoveToEx(hdc, (int)x, (int)y, NULL);
}
return 0;
}
void draw() {
while (deg < 360) {
deg += INCERMENT_DEG;
nextPoint(deg, &x, &y);
if (meth == DRAW_RADII) {
MoveToEx(hdc, centerX, centerY, NULL);
LineTo(hdc, (int)x, (int)y);
} else if (meth == DRAW_POLY) {
LineTo(hdc, (int)x, (int)y);
} else
break;
Sleep(ITERATION_SLEEP_TIME);
}
}
void cleanup() {
if (hpen) {
DeleteObject(hpen);
}
if (hwnd && hdc) {
ReleaseDC(hwnd, hdc);
}
}
int main() {
if (!init())
draw();
cleanup();
return 0;
}