How could I fill in my circle with a solid color using the distance formula? - c++

Question

I am a beginner in c++ and have coded a for loop to show a hollow circle when I run the code, however, I was wondering how I could achieve a filled-in circle using the distance formula (d = sqrt((ax-bx)^2 + (ay-by)^2). Here's what I have so far! Any help would be appreciated!
int MAX = 728;
for (float t = 0; t < 2 * 3.14; t += 0.01)
SetPixel(MAX / 4 + MAX / 6 * sin(t), MAX / 4 + MAX / 6 * cos(t), 255, 255, 0);

Answer 1

#include <windows.h>
#include <iostream>
using namespace std;
int main()
{
HWND consoleWindow = GetConsoleWindow(); // Get a console handle
HDC consoleDC = GetDC(consoleWindow); // Get a handle to device context
int max = 628;
float i = 0;
float t;
float doublePi = 6.29;
for (i = 0.0; i < max; i += 2.0) {
for (t = 0.0; t < doublePi; t += 0.01) {
SetPixel(consoleDC, max / 4 + (max - i) / 6 * sin(t), max / 4 + (max - i) / 6 * cos(t), RGB(255, 255, 0));
}
}
ReleaseDC(consoleWindow, consoleDC);
cin.ignore();
return 0;
}
Working almost well. Draw and fill in! A little slow...

Answer 2

Pffff... do not use sin and cos! instead use the sqrt(1-x^2) approach. You can view the formula rendering a circle in google for example: https://www.google.com/search?q=sqrt(1-x^2)
I edit this answer because it seems that is not clear:
float radius = 50.0f;
for (int x = -radius; x <= radius; ++x) {
int d = round(sqrt(1.0f - (x * x / radius / radius)) * radius);
for (int y = -d; y <= d; ++y) {
SetPixel(x, y, 255, 255, 0);
}
}
Note: each graphic library is different, so I assumed that you used rightfully the "SetPixel" function.
Now, for most people say the sqrt(1-x^2) approach should be enough, but it seem that some downvoters does not think the same XD.

Answer 3

Inefficient as can be, and probably the last way you really want to draw a circle ... but ...
Over the entire square encompassing your circle, calculate each pixel's distance from the center and set if under or equal the radius.
// Draw a circle centered at (Xcenter,Ycenter) with given radius using distance formula
void drawCircle(HDC dc, int XCenter, int YCenter, int radius, COLORREF c) {
double fRad = radius * 1.0; // Just a shortcut to avoid thrashing data types
for (int x = XCenter - radius; x<XCenter + radius; x++) {
for (int y = YCenter - radius; y<YCenter + radius; y++) {
double d = sqrt(((x - XCenter) * (x - XCenter)) + ((y - YCenter) * (y - YCenter)) );
if (d <= fRad) SetPixel(dc, x, y, c);
}
}
}
Caveat: No more caveat, used a C++ environment and tested it this time. :-)
Call thusly:
int main()
{
HWND consoleWindow = GetConsoleWindow();
HDC consoleDC = GetDC(consoleWindow);
drawCircle(consoleDC, 50, 50, 20, RGB(255, 0, 255));
ReleaseDC(consoleWindow, consoleDC);
return 0;
}