Writing PNG file from pixel data using libpng - c++

Question

I am trying to write PNG file (saving an image in png format) from pixel data read by glReadPixels in openGL using following piece of code (copied from here):
bool writePNGFileFromBuffer(const char *filename, unsigned char *pixels, int w, int h)
{
png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);//8
if (!png)
return false;
png_infop info = png_create_info_struct(png);//7
if (!info) {
png_destroy_write_struct(&png, &info);//
return false;
}
FILE *fp = fopen(filename, "wb");
if (!fp) {
png_destroy_write_struct(&png, &info);//
return false;
}
png_init_io(png, fp);//9
png_set_IHDR(png, info, w, h, 8 /* depth */, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);//10
png_colorp palette = (png_colorp)png_malloc(png, PNG_MAX_PALETTE_LENGTH * sizeof(png_color));//4
if (!palette) {
fclose(fp);
png_destroy_write_struct(&png, &info);//
return false;
}
png_set_PLTE(png, info, palette, PNG_MAX_PALETTE_LENGTH);//12
png_write_info(png, info);//1
png_set_packing(png);//5
png_bytepp rows = (png_bytepp)png_malloc(png, h * sizeof(png_bytep));//
for (int i = 0; i < h; ++i)
rows[i] = (png_bytep)(pixels + (h - i) * w * 3);
png_write_image(png, rows);//2
png_write_end(png, info);//6
png_free(png, palette);//11
png_destroy_write_struct(&png, &info);//3
fclose(fp);
delete[] rows;
return true;
}
I linked the libpng and zlib libraries in the additional dependencies. But when I compile the code it gives following error:
Error 77 error LNK2001: unresolved external symbol png_write_info
It gives this error at about 12 instances marked in the code snippet above. I am clear that it is not able to find the definitions of the functions but I do not know why?
Any help would be appreciated. Thanks
Edit: I looked into the header file "png.h" and it contains declarations for all the functions. Functions are defined in "pngwrite.c" and I think it should take it from the linked library.
Edit2: After hitting around for couple of days, I found that when I change the output type of my project (in which I am using libpng.lib) to Static Lib (.lib), everything works and the code compiles well but with .dll output it throws the above specified error.
And my problem is, I have to use .dll output because that I use in another huge project which I cant change to accept .lib.
Any help on this?

Answer 1

You may be missing "pnglibconf.h" which you must copy from
scripts/pnglibconf.h.prebuilt to pnglibconf.h in your source directory.