write a c++ bitmap image file

[Ramees219]

hi i am trying to write a bitmap image with a circle in it in c++ i don't no where to start it then i found some code in stackoverflow i like to use this code and write a circle or a rectangle in and save this file as a .bmp file format i have some complicated data need to write into this bitmap file to do that i need a full working solution i need help to complete this code and i don't understand this line ( long red = lround(255.0 * waterfall[x][y]); )
thanks

#include <iostream>
#include <ostream>
#include <fstream>

using namespace std;

unsigned char file[14] = {
	'B','M', // magic
	0,0,0,0, // size in bytes
	0,0, // app data
	0,0, // app data
	40 + 14,0,0,0 // start of data offset
};
unsigned char info[40] = {
	40,0,0,0, // info hd size
	0,0,0,0, // width
	0,0,0,0, // heigth
	1,0, // number color planes
	24,0, // bits per pixel
	0,0,0,0, // compression is none
	0,0,0,0, // image bits size
	0x13,0x0B,0,0, // horz resoluition in pixel / m
	0x13,0x0B,0,0, // vert resolutions (0x03C3 = 96 dpi, 0x0B13 = 72 dpi)
	0,0,0,0, // #colors in pallete
	0,0,0,0, // #important colors
};



int main() {

	ofstream stream;

	// mimeType = "image/bmp";
	unsigned int const waterfallWidth = 256;
	unsigned int const waterfallHeight = 256;

	int w = waterfallWidth;
	int h = waterfallHeight;

	int waterfall[waterfallWidth][waterfallHeight];

	int padSize = (4 - (w * 3) % 4) % 4;
	int sizeData = w*h * 3 + h*padSize;
	int sizeAll = sizeData + sizeof(file) + sizeof(info);

	file[2] = (unsigned char)(sizeAll);
	file[3] = (unsigned char)(sizeAll >> 8);
	file[4] = (unsigned char)(sizeAll >> 16);
	file[5] = (unsigned char)(sizeAll >> 24);

	info[4] = (unsigned char)(w);
	info[5] = (unsigned char)(w >> 8);
	info[6] = (unsigned char)(w >> 16);
	info[7] = (unsigned char)(w >> 24);

	info[8] = (unsigned char)(h);
	info[9] = (unsigned char)(h >> 8);
	info[10] = (unsigned char)(h >> 16);
	info[11] = (unsigned char)(h >> 24);

	info[20] = (unsigned char)(sizeData);
	info[21] = (unsigned char)(sizeData >> 8);
	info[22] = (unsigned char)(sizeData >> 16);
	info[23] = (unsigned char)(sizeData >> 24);



	stream.write((char*)file, sizeof(file));
	stream.write((char*)info, sizeof(info));

	unsigned char pad[3] = { 0,0,0 };

	for (int y = 0; y<h; y++)
	{
		for (int x = 0; x<w; x++)
		{
			long red = lround(255.0 * waterfall[x][y]);
			if (red < 0) red = 0;
			if (red > 255) red = 255;
			long green = red;
			long blue = red;

			unsigned char pixel[3];
			pixel[0] = blue;
			pixel[1] = green;
			pixel[2] = red;
			
			stream.write((char*)pixel, 3);
		}
		stream.write((char*)pad, padSize);
	}




	return 0;
}

[2kaud]

lround() rounds a floating point value to the nearest long integer. See https://msdn.microsoft.com/en-us/library/dn329049.aspx

[Ramees219]

lround() rounds a floating point value to the nearest long integer. See https://msdn.microsoft.com/en-us/library/dn329049.aspx

ok why this values multiplying 255.0 * waterfall[x][y]

[2kaud]

The array waterfall[] is not initialised so contains random values from whatever happens to be in memory. So

long red = lround(255.0 * waterfall[x][y]);
if (red < 0) red = 0;
if (red > 255) red = 255;

sets red to be a long int with a value between 0 and 255 inclusive.

[2kaud]

Each pixel is made up of red, green and blue (R G B) and the values for these range from 0 to 255 - with 0 meaning that colour is not present and 255 the maximum colour intensity. Other colours are obtained by varying the values for these red, green and blue. eg white is (255, 255, 255), black is (0, 0, 0), yellow is (255, 255, 0) and cyan is (0, 255, 255) etc.

[Ramees219]

1, what is pad size ( int padSize = (4 - (w * 3) % 4) % 4 )

2, what is the meaning of 8 , 16, 24 in below code

        file[2] = (unsigned char)(sizeAll);
	file[3] = (unsigned char)(sizeAll >> 8);
	file[4] = (unsigned char)(sizeAll >> 16);
	file[5] = (unsigned char)(sizeAll >> 24);

	info[4] = (unsigned char)(w);
	info[5] = (unsigned char)(w >> 8);
	info[6] = (unsigned char)(w >> 16);
	info[7] = (unsigned char)(w >> 24);

3, how can i save this stream into a file

[2kaud]

info[4] = (unsigned char)(w);
info[5] = (unsigned char)(w >> 8);
info[6] = (unsigned char)(w >> 16);
info[7] = (unsigned char)(w >> 24);

if you look at where info[] is defined, bytes 4, 5, 6 & 7 are the width. This codes takes an int w (and assumes it is 32 bits - 4 bytes!) and sets info[4] to info[7] to the individual bytes of the 4 byte int. w >> 8 means right shift w by 8 bits ie put in byte 0 what is byte 1. The unsigned char cast returns the value of byte 0. So w >> 16 shifts right by 16 bits so byte 2 is put into byte 0 etc etc. One byte is 8 bits.

[Ramees219]

when i change image width & height 256 to 1024 getting an error i am using visual studio 2015

#include <iostream>
#include <ostream>
#include <fstream>

using namespace std;

unsigned char file[14] = {
	'B','M', // magic
	0,0,0,0, // size in bytes
	0,0, // app data
	0,0, // app data
	40 + 14,0,0,0 // start of data offset
};
unsigned char info[40] = {
	40,0,0,0, // info hd size
	0,0,0,0, // width
	0,0,0,0, // heigth
	1,0, // number color planes
	24,0, // bits per pixel
	0,0,0,0, // compression is none
	0,0,0,0, // image bits size
	0x13,0x0B,0,0, // horz resoluition in pixel / m
	0x13,0x0B,0,0, // vert resolutions (0x03C3 = 96 dpi, 0x0B13 = 72 dpi)
	0,0,0,0, // #colors in pallete
	0,0,0,0, // #important colors
};



int main() {

	ofstream stream ("Myimage.bmp",std::ios::binary);

	// mimeType = "image/bmp";
	unsigned int const waterfallWidth = 1024;
	unsigned int const waterfallHeight = 1024;

	int w = waterfallWidth;
	int h = waterfallHeight;

	int waterfall[waterfallWidth][waterfallHeight];

	int padSize = (4 - (w * 3) % 4) % 4;
	int sizeData = w*h * 3 + h*padSize;
	int sizeAll = sizeData + sizeof(file) + sizeof(info);

	file[2] = (unsigned char)(sizeAll);
	file[3] = (unsigned char)(sizeAll >> 8);
	file[4] = (unsigned char)(sizeAll >> 16);
	file[5] = (unsigned char)(sizeAll >> 24);

	info[4] = (unsigned char)(w);
	info[5] = (unsigned char)(w >> 8);
	info[6] = (unsigned char)(w >> 16);
	info[7] = (unsigned char)(w >> 24);

	info[8] = (unsigned char)(h);
	info[9] = (unsigned char)(h >> 8);
	info[10] = (unsigned char)(h >> 16);
	info[11] = (unsigned char)(h >> 24);

	info[20] = (unsigned char)(sizeData);
	info[21] = (unsigned char)(sizeData >> 8);
	info[22] = (unsigned char)(sizeData >> 16);
	info[23] = (unsigned char)(sizeData >> 24);



	stream.write((char*)file, sizeof(file));
	stream.write((char*)info, sizeof(info));

	unsigned char pad[3] = { 0,0,0 };

	for (int y = 0; y<h; y++)
	{
		for (int x = 0; x<w; x++)
		{
			/*long red = lround(255.0 * waterfall[x][y]);
			if (red < 0) red = 0;
			if (red > 255) red = 255;
			long green = red;
			long blue = red;*/

			unsigned char pixel[3];
			pixel[0] = 35;
			pixel[1] = 65;
			pixel[2] = 1;
			
			stream.write((char*)pixel, 3);
		}
		stream.write((char*)pad, padSize);
	}

	stream.close();


	return 0;
}

i want image to be 1024 * 1024 and why i am getting error

[2kaud]

I've cleaned up the code somewhat. This now compiles and runs under VS2015 and produces a .bmp file with the specified background colour of the required size.

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

const string bmpnam = "Myimage.bmp";

unsigned int const bmpWidth = 1024;
unsigned int const bmpHeight = 1024;

unsigned char file[14] = {
	'B','M',	        // magic
	0, 0, 0, 0,		// size in bytes
	0, 0,			// app data
	0, 0,			// app data
	40 + 14, 0, 0, 0	// start of data offset
};

unsigned char info[40] = {
	40, 0, 0, 0,	        // info size
	0, 0, 0, 0,		// width
	0, 0 ,0, 0,		// height
	1, 0,			// number color planes
	24, 0,		        // bits per pixel
	0, 0, 0, 0,		// compression is none
	0, 0, 0, 0,		// image bits size
	0x13, 0x0B, 0, 0,       // horz resolution in pixel / m
	0x13, 0x0B, 0, 0,       // vert resolutions (0x03C3 = 96 dpi, 0x0B13 = 72 dpi)
	0, 0, 0, 0,		// #colors in pallet
	0, 0, 0, 0,		// #important colors
};

void setInt(unsigned char* mem, int data)
{
	for (int i = 0; i < sizeof(data); ++i)
		*mem++ = (unsigned char)(data >> (8 * i));
}

int main()
{
	ofstream stream(bmpnam, std::ios::binary);

	if (!stream.is_open()) {
		cout << "Cannot open stream" << endl;
		return 1;
	}

	const int padSize = (4 - (bmpWidth * 3) % 4) % 4;
	const int sizeData = bmpWidth * bmpHeight * 3 + bmpHeight * padSize;
	const int sizeAll = sizeData + sizeof(file) + sizeof(info);

	setInt(&file[2], sizeAll);
	setInt(&info[4], bmpWidth);
	setInt(&info[8], bmpHeight);
	setInt(&info[20], sizeData);

	stream.write((char*)file, sizeof(file));
	stream.write((char*)info, sizeof(info));

	const char pad[3] = {0};
	const char backrgb[3] = { 35, 65, 1 };

	for (int y = 0; y < bmpHeight; ++y) {
		for (int x = 0; x < bmpWidth; ++x)
			stream.write(backrgb, 3);

		stream.write(pad, padSize);
	}

	stream.close();

	return 0;
}

Have fun!

[Ramees219]

thanks