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dev578

Using GDI functions and saving them as a bitmap

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I want to be able to use GDI functions to make graphics and save it to a bitmap file. However, the bitmap can be much larger than the screen, so I don't think I can just do it on a screen DC and then copy it to a bitmap. The following code is a test to see how to write something to a bitmap. I try to do a square in the top left of the bitmap. There is a square written in the correct-ish area, but it is just a mix of black and white pixels. I am using the bitsperpixel of the DC, which isn't monochrome. Also, the area of the bitmap where the rectangle isn't is solid black. Here is the code:
int Width = 640*Screens;
int Height = 480;

HDC hScreenDC = GetWindowDC(0);
HDC BmpHDC = CreateCompatibleDC(hScreenDC);
HBITMAP hmemBM = CreateCompatibleBitmap(BmpHDC, Width, Height);
HBRUSH hBrush = CreateSolidBrush(RGB(195,55,87));
SelectObject(BmpHDC,hBrush);
SelectObject(BmpHDC,hmemBM);

//Polyline(BmpHDC,pt,640*Screens);
Rectangle(BmpHDC,1,1,101,101);

int BytesPerPixel = (int)GetDeviceCaps(BmpHDC,BITSPIXEL);

HGLOBAL hpxldata = GlobalAlloc(GMEM_FIXED, Width*Height*BytesPerPixel);
void FAR* lpvpxldata = GlobalLock(hpxldata);

BITMAPINFO bmInfo;
bmInfo.bmiHeader.biSize = 40;
bmInfo.bmiHeader.biWidth = Width;
bmInfo.bmiHeader.biHeight = Height;
bmInfo.bmiHeader.biPlanes = 1;
bmInfo.bmiHeader.biBitCount = BytesPerPixel;//24
bmInfo.bmiHeader.biCompression = 0;
bmInfo.bmiHeader.biSizeImage = 0;
bmInfo.bmiHeader.biXPelsPerMeter = 0;
bmInfo.bmiHeader.biYPelsPerMeter = 0;
bmInfo.bmiHeader.biClrUsed = 0;
bmInfo.bmiHeader.biClrImportant = 0;

BITMAPFILEHEADER bmFileHeader;
bmFileHeader.bfType = 19778;
bmFileHeader.bfSize = (Width*Height*BytesPerPixel) + 40 + 14;
bmFileHeader.bfReserved1 = 0;
bmFileHeader.bfReserved2 = 0;
bmFileHeader.bfOffBits = 54;

GetDIBits(BmpHDC, hmemBM, 0, Height, lpvpxldata, &bmInfo, DIB_RGB_COLORS);

FILE *fp = fopen("Bitmap.bmp","wb");
fwrite(&bmFileHeader,1,14,fp);
fwrite(&bmInfo,1,40,fp);
fwrite(lpvpxldata,1,Width*Height*BytesPerPixel,fp);
fclose(fp);

GlobalUnlock(hpxldata);
GlobalFree(hpxldata);
DeleteObject(hmemBM);
DeleteObject(hBrush);
DeleteDC(BmpHDC);
ReleaseDC(0, hScreenDC);

Any ideas? Also, after looking around a bit, CreateDIBSection() might be a better alternative? I just have no clue how to implement it, there doesn't seem to be any good documentation. Thank you, Dev578

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