How can I save OpenGL draw with OpenGL?

Question

I draw a screen with OpenGL commands. And I must save this screen to .bmp or .png format. But I can\'t do it. I am using glReadpixels but I can\'t do continue. How can I sav

Answer 1

Unless you're feeling particularly ambitious (or perhaps masochistic) you probably want to use a library like DevIL that already supports this. The current version can load and/or save in both PNG and BMP formats, along with a few dozen others.

Compared to something like IJG, this is oriented much more heavily toward working with OpenGL or DirectX (e.g., it can load a file fairly directly into an texture or vice versa).

Answer 2

I know you're asking for raster formats, but an indirect way would be to first output vector graphics through gl2ps (http://www.geuz.org/gl2ps/). Examples of usage are provided with the package and on the site (http://www.geuz.org/gl2ps/#tth_sEc3).

Then, the vector output can be converted to the format of your choice using another tool (Inkscape, Image/GraphicsMagick, etc.) or library. An added benefit is you can convert to bitmaps of any resolution in the future.

Answer 3

Here it comes! you must include WinGDI.h (which i think the GL will do it!)

void SaveAsBMP(const char *fileName)
{
    FILE *file;
    unsigned long imageSize;
    GLbyte *data=NULL;
    GLint viewPort[4];
    GLenum lastBuffer;
    BITMAPFILEHEADER bmfh;
    BITMAPINFOHEADER bmih;
    bmfh.bfType='MB';
    bmfh.bfReserved1=0;
    bmfh.bfReserved2=0;
    bmfh.bfOffBits=54;
    glGetIntegerv(GL_VIEWPORT,viewPort);
    imageSize=((viewPort[2]+((4-(viewPort[2]%4))%4))*viewPort[3]*3)+2;
    bmfh.bfSize=imageSize+sizeof(bmfh)+sizeof(bmih);
    data=(GLbyte*)malloc(imageSize);
    glPixelStorei(GL_PACK_ALIGNMENT,4);
    glPixelStorei(GL_PACK_ROW_LENGTH,0);
    glPixelStorei(GL_PACK_SKIP_ROWS,0);
    glPixelStorei(GL_PACK_SKIP_PIXELS,0);
    glPixelStorei(GL_PACK_SWAP_BYTES,1);
    glGetIntegerv(GL_READ_BUFFER,(GLint*)&lastBuffer);
    glReadBuffer(GL_FRONT);
    glReadPixels(0,0,viewPort[2],viewPort[3],GL_BGR,GL_UNSIGNED_BYTE,data);
    data[imageSize-1]=0;
    data[imageSize-2]=0;
    glReadBuffer(lastBuffer);
    file=fopen(fileName,"wb");
    bmih.biSize=40;
    bmih.biWidth=viewPort[2];
    bmih.biHeight=viewPort[3];
    bmih.biPlanes=1;
    bmih.biBitCount=24;
    bmih.biCompression=0;
    bmih.biSizeImage=imageSize;
    bmih.biXPelsPerMeter=45089;
    bmih.biYPelsPerMeter=45089;
    bmih.biClrUsed=0;
    bmih.biClrImportant=0;
    fwrite(&bmfh,sizeof(bmfh),1,file);
    fwrite(&bmih,sizeof(bmih),1,file);
    fwrite(data,imageSize,1,file);
    free(data);
    fclose(file);
}

Answer 4

One thing need to be fixed at:

bmih.biXPelsPerMeter = bmih.biYPelsPerMeter = 0;

Otherwise, some picture edit can not open correctly.