I should have came back to this sooner, I got it working, the code is still in my Pokittaire game. I think the issue was something about not including the correct headers, or the build settings were slightly wrong or something like that.
bool saveBMP(char* filename){
// no longer used
char w=110, h=88;
FILE *f;
int filesize = 54 + 3*w*h; //w is your image width, h is image height, both int
unsigned char bmpfileheader[14] = {'B','M', 0,0,0,0, 0,0, 0,0, 54,0,0,0};
unsigned char bmpinfoheader[40] = {40,0,0,0, 0,0,0,0, 0,0,0,0, 1,0, 24,0};
unsigned char bmppad[3] = {0,0,0};
bmpfileheader[ 2] = (unsigned char)(filesize );
bmpfileheader[ 3] = (unsigned char)(filesize>> 8);
bmpfileheader[ 4] = (unsigned char)(filesize>>16);
bmpfileheader[ 5] = (unsigned char)(filesize>>24);
bmpinfoheader[ 4] = (unsigned char)( w );
bmpinfoheader[ 5] = (unsigned char)( w>> 8);
bmpinfoheader[ 6] = (unsigned char)( w>>16);
bmpinfoheader[ 7] = (unsigned char)( w>>24);
bmpinfoheader[ 8] = (unsigned char)( h );
bmpinfoheader[ 9] = (unsigned char)( h>> 8);
bmpinfoheader[10] = (unsigned char)( h>>16);
bmpinfoheader[11] = (unsigned char)( h>>24);
f = fopen(filename,"wb");
fwrite(bmpfileheader,1,14,f);
fwrite(bmpinfoheader,1,40,f);
for(int y=0; y<h; y++){
for(int x=0; x<w; x++){
int pix = game.display.getPixel(x,h-y-1);
int color = game.display.palette[pix];
char r = ((((color >> 11) & 0x1F) * 527) + 23) >> 6;
char g = ((((color >> 5) & 0x3F) * 259) + 33) >> 6;
char b = (((color & 0x1F) * 527) + 23) >> 6;
fwrite(&b , 1 , sizeof(b) , f);
fwrite(&g , 1 , sizeof(g) , f);
fwrite(&r , 1 , sizeof(r) , f);
}
fwrite(bmppad,1,(4-(w*3)%4)%4,f);
}
fclose(f);
}
