CODEWITHSUNDEEP
c++arraysdrawgeometry
tinyJman
tinyJman

Reputation: 23

Trying to create a circle within a 2D array

I'm trying to write a program for creating .pgm and .ppm and am trying to draw a circle using a 2D array of numbers. Using a given center location (x,y) and the radius. Here is what my code looks like for the drawCircle() function.

void drawCircle(unsigned char pgmImage[][WIDTH], int height, int centerX, int centerY, int radius, unsigned char grayLevel) {

for (int rowIndex = centerY; rowIndex < 50; rowIndex++) {
    for (int colIndex = centerX; colIndex < 50; colIndex++) {
        if ((pow(colIndex - centerX, 2)) + (pow(rowIndex - centerY, 2)) <= pow(radius, 2)) {
            pgmImage[rowIndex][colIndex] = (grayLevel);
        }
    }
}

The grayLevel is for what shade of grey I want the circle to be. and I am attempting to draw the circle using the formula (x-a)^2 + (y-b)^2 =r^2 where a and b are my center x and y.

Upvotes: 0

Views: 3111

Answers (3)

VideoProcessingResearcher
VideoProcessingResearcher

Reputation: 556

I modified previous example and now it draws all 4 parts of circle.

#include <math.h>
#include <string>
#include <iostream>
#include <conio.h>

using namespace std;

const int HEIGHT = 50, WIDTH = 50;

void drawCircle(unsigned char pgmImage[][WIDTH], int height, int centerX, int centerY, int radius, unsigned char grayLevel)
{

    for (int rowIndex = centerY; rowIndex < HEIGHT; rowIndex++)
    {
        for (int colIndex = centerX; colIndex < WIDTH; colIndex++)
        {
            if ((pow(1.0*(colIndex - centerX), 2)) + (pow(1.0*(rowIndex - centerY), 2)) <= pow(1.0*radius, 2))
            {
                pgmImage[rowIndex][colIndex] = (grayLevel);
            }
        }
    }
    for (int rowIndex = 0; rowIndex < centerY; rowIndex++)
    {
        for (int colIndex = 0; colIndex < centerX; colIndex++)
        {
                if ((pow(1.0*(colIndex - centerX), 2)) + (pow(1.0*(rowIndex - centerY), 2)) <= pow(1.0*radius, 2))
                {
                    pgmImage[rowIndex][colIndex] = (grayLevel);
                }
        }
    }
    for (int rowIndex = 0; rowIndex < centerY; rowIndex++)
    {
        for (int colIndex = centerX; colIndex < WIDTH; colIndex++)
        {
            if ((pow(1.0*(colIndex - centerX), 2)) + (pow(1.0*(rowIndex - centerY), 2)) <= pow(1.0*radius, 2))
            {
                pgmImage[rowIndex][colIndex] = (grayLevel);
            }
        }
    }
    for (int rowIndex = centerY; rowIndex < HEIGHT; rowIndex++)
    {
        for (int colIndex = 0; colIndex < centerX; colIndex++)
        {
            if ((pow(1.0*(colIndex - centerX), 2)) + (pow(1.0*(rowIndex - centerY), 2)) <= pow(1.0*radius, 2))
            {
                pgmImage[rowIndex][colIndex] = (grayLevel);
            }
        }
    }
}


int _tmain(int argc, _TCHAR* argv[])
{
    unsigned char pgmImage[HEIGHT][WIDTH] = { {0} };
    int centerY = HEIGHT/2;
    int centerX = WIDTH/2;
    int radius = std::min(centerX,centerY) - 1;

    drawCircle(pgmImage, HEIGHT, centerX, centerY, radius, 1);
    for (int r=0;r<HEIGHT;r++)
    {
        for (int c=0;c<WIDTH;c++)
        {
            char o = (pgmImage[r][c] != 0) ? 'X' : '-';
            cout << o;
        }
        cout << endl;
    }
    getch();
    return 0;
}

Upvotes: 0

Joseph D.
Joseph D.

Reputation: 12174

I see the problem when your center is greater than 50.

Your loop initialization starts at center.

However, you hard-coded the condition to be always less than 50 which will be false.

Perhaps you want to start from (0, 0), until ((height - 1), (width - 1))

eg.

rowIndex (0, height]
colIndex: (0, width]

CODE SNIPPET

for (int rowIndex = 0; rowIndex < height; rowIndex++) {
    for (int colIndex = 0; colIndex < width; colIndex++) {

Upvotes: 1

Stephan Lechner
Stephan Lechner

Reputation: 35154

I think you code should work fine, provided that you calculate the parameters correctly:

constexpr int HEIGHT = 50, WIDTH = 50;

void drawCircle(unsigned char pgmImage[][WIDTH], int height, int centerX, int centerY, int radius, unsigned char grayLevel) {

    for (int rowIndex = centerY; rowIndex < 50; rowIndex++) {
        for (int colIndex = centerX; colIndex < 50; colIndex++) {
            if ((pow(colIndex - centerX, 2)) + (pow(rowIndex - centerY, 2)) <= pow(radius, 2)) {
                pgmImage[rowIndex][colIndex] = (grayLevel);
            }
        }
    }
}

int main() {

    unsigned char pgmImage[HEIGHT][WIDTH] = { {0} };
    int centerY = HEIGHT/2;
    int centerX = WIDTH/2;
    int radius = min(centerX,centerY) - 1;

    drawCircle(pgmImage, HEIGHT, centerX, centerY, radius, 1);
    for (int r=0;r<HEIGHT;r++) {
        for (int c=0;c<WIDTH;c++) {
            char o = (pgmImage[r][c] != 0) ? 'X' : '-';
            cout << o;
        }
        cout << endl;
    }
}

Output:

--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
--------------------------------------------------
-------------------------XXXXXXXXXXXXXXXXXXXXXXXXX
-------------------------XXXXXXXXXXXXXXXXXXXXXXXX-
-------------------------XXXXXXXXXXXXXXXXXXXXXXXX-
-------------------------XXXXXXXXXXXXXXXXXXXXXXXX-
-------------------------XXXXXXXXXXXXXXXXXXXXXXXX-
-------------------------XXXXXXXXXXXXXXXXXXXXXXXX-
-------------------------XXXXXXXXXXXXXXXXXXXXXXXX-
-------------------------XXXXXXXXXXXXXXXXXXXXXXX--
-------------------------XXXXXXXXXXXXXXXXXXXXXXX--
-------------------------XXXXXXXXXXXXXXXXXXXXXXX--
-------------------------XXXXXXXXXXXXXXXXXXXXXX---
-------------------------XXXXXXXXXXXXXXXXXXXXXX---
-------------------------XXXXXXXXXXXXXXXXXXXXX----
-------------------------XXXXXXXXXXXXXXXXXXXXX----
-------------------------XXXXXXXXXXXXXXXXXXXX-----
-------------------------XXXXXXXXXXXXXXXXXXX------
-------------------------XXXXXXXXXXXXXXXXXX-------
-------------------------XXXXXXXXXXXXXXXXX--------
-------------------------XXXXXXXXXXXXXXXX---------
-------------------------XXXXXXXXXXXXXXX----------
-------------------------XXXXXXXXXXXXXX-----------
-------------------------XXXXXXXXXXXX-------------
-------------------------XXXXXXXXXX---------------
-------------------------XXXXXXX------------------
-------------------------X------------------------

Upvotes: 1

Related Questions