Thread: questions about bitmap edit

I would like to write a program that can ask for an x,y coordinates and hence draw circle on a imported bitmap.
It can draw circles on the imported bitmap and show the image after each edit.
I have done most part about how to read and allocate memories of bitmap,
but I got difficulties with how to draw circles and how to save the result image as output.bmp
I wish I can have help with void SaveFile and void DrawCircle.
Thank you for any help.

Code:

#pragma pack(push, 1)
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>


typedef int32_t int32;
typedef int16_t int16;
typedef uint8_t byte;


typedef struct {
    byte      signatureB;        
    byte      signatureM;        
    int32     fileSize;            
    int16     reserved1;        
    int16     reserved2;        
    int32     imageOffset;        
} BMPHeader;


typedef struct {
    int32     size;                
    int32     imageWidth;        
    int32     imageHeight;        
    int16     colorPlanes;        
    int16     bitsPerPixel;        
    byte      extra[24];
} BMPInfoHeader;


typedef struct {
    byte blue;
    byte green;
    byte red;
} Pixel;


BMPHeader bmpHeader;                
BMPInfoHeader bmpInfoHeader;        


Pixel* LoadBitmap(char* bmpFilename) {
    FILE *filePtr;                        
    Pixel *bitmapImage = NULL; 
    
    
    filePtr = fopen(bmpFilename, "rb");
    if (filePtr == NULL) {
        printf("Input bitmap not found...it should be in your project directory or same directory as your exe if stand-alone\n");
        return NULL;
    }


    
    fread(&bmpHeader, sizeof(BMPHeader), 1, filePtr);


    if (bmpHeader.signatureB != 'B' || bmpHeader.signatureM != 'M') {
        printf("Input file not a BMP... have you saved it properly as a bitmap file?\n");
        fclose(filePtr);
        return NULL;
    }


    printf("Reported file size: %d\n", bmpHeader.fileSize);
    printf("Offset for image data: %d\n", bmpHeader.imageOffset);


    
    fread(&bmpInfoHeader, sizeof(BMPInfoHeader), 1, filePtr);
    if (bmpInfoHeader.bitsPerPixel != 24) {
        printf("Input file not 24-bit BMP... Plese save as 24 bit BMP only\n");
        fclose(filePtr);
        return NULL;
    }
    
    printf("Reported image width: %d\n", bmpInfoHeader.imageWidth);
    printf("Reported image height: %d\n", bmpInfoHeader.imageHeight);
    printf("Number of bits per pixel: %d\n", bmpInfoHeader.bitsPerPixel);


    
    fseek(filePtr, bmpHeader.imageOffset, SEEK_SET);


    
    int imageSize = bmpInfoHeader.imageWidth*bmpInfoHeader.imageHeight*3; 
    printf("Image size: %d\n", imageSize);
    bitmapImage = (Pixel*)malloc(imageSize);
    
    
    fread(bitmapImage, sizeof(Pixel), bmpInfoHeader.imageWidth*bmpInfoHeader.imageHeight, filePtr);
    
    fclose(filePtr);
    return bitmapImage;
}


void SaveFile(char* filename) {
}    

void DrawCircle(){
}


void ShowImage(Pixel* image) {
    


    int i, j;
    
    for (i = bmpInfoHeader.imageHeight-1; i >= 0; i--) {
        for (j = 0; j < bmpInfoHeader.imageWidth; j++) {
            Pixel p = image[i*bmpInfoHeader.imageWidth + j];  
            
            double mono = (0.2125 * p.red + 0.7154 * p.green + 0.0721 * p.blue)/255;    // convert to monochrome


            if (mono < 0.2) {
                printf("%c", ' ');
            } else if (mono < 0.4) {
                printf("%c", 176);
            } else if (mono < 0.6) {
                printf("%c", 177);
            } else {
                printf("%c", 178);
            }
            
        }
        printf("\n");
    }


}
    


int main(void) {
    system("chcp 437");        
    Pixel* image = LoadBitmap("input.bmp");


    printf("\nTop-Left Pixel -               Blue: %d Green: %d Red: %d\n", image[0].blue, image[0].green, image[0].red); // example
    printf("Pixel next to Top-Left Pixel - Blue: %d Green: %d Red: %d\n\n", image[1].blue, image[1].green, image[1].red); // example


    printf("Please enter the coordinates of the circle center x,y \n Entering 0 for both x and y to quit and save the output");
    int x, y;
    scanf("%d%d", &x, &y);
    while (x != 0 || y != 0){
        char ch = getchar();
        DrawCircle();
        ShowImage(image);
        printf("Please enter the coordinates of the circle center x,y \n Entering 0 for both x and y to quit and save the output");
        scanf("%d%d", &x, &y);
    }
    SaveFile("output.bmp");
}