掌機 - GKD Pixel - 解決Invalid use of incomplete typedef png_info問題

參考資訊：
https://refspecs.linuxbase.org/LSB_3.1.0/LSB-Desktop-generic/LSB-Desktop-generic/libpng12man.html

問題如下：

scripts/png2logo.c:5:6: warning: no previous prototype for ‘gen_info’ [-Wmissing-prototypes]
    5 | void gen_info(int w, int h, int bpp, int backcolor)
      |      ^~~~~~~~
scripts/png2logo.c:26:6: warning: no previous prototype for ‘ReadPng’ [-Wmissing-prototypes]
   26 | void ReadPng(const char *png_file, int real_bit_dep ,int backcolor)
      |      ^~~~~~~
scripts/png2logo.c: In function ‘ReadPng’:
scripts/png2logo.c:51:42: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   51 |         unsigned int pixel_num = info_ptr->height * info_ptr->width;
      |                                          ^~
scripts/png2logo.c:51:61: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   51 |         unsigned int pixel_num = info_ptr->height * info_ptr->width;
      |                                                             ^~
scripts/png2logo.c:56:26: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   56 |         gen_info(info_ptr->width, info_ptr->height, real_bit_dep, backcolor);
      |                          ^~
scripts/png2logo.c:56:43: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   56 |         gen_info(info_ptr->width, info_ptr->height, real_bit_dep, backcolor);
      |                                           ^~
scripts/png2logo.c:59:40: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   59 |                 for(i = 0; i < info_ptr->height; i++)
      |                                        ^~
scripts/png2logo.c:61:51: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   61 |                         for(j = 0; j < ( (info_ptr->pixel_depth / 8) * info_ptr->width); j += (info_ptr->pixel_depth / 8) )
      |                                                   ^~
scripts/png2logo.c:61:80: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   61 |                         for(j = 0; j < ( (info_ptr->pixel_depth / 8) * info_ptr->width); j += (info_ptr->pixel_depth / 8) )
      |                                                                                ^~
scripts/png2logo.c:61:104: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   61 |                         for(j = 0; j < ( (info_ptr->pixel_depth / 8) * info_ptr->width); j += (info_ptr->pixel_depth / 8) )
      |                                                                                                        ^~
scripts/png2logo.c:64:44: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   64 |                                 if(info_ptr->pixel_depth == 32){
      |                                            ^~
scripts/png2logo.c:69:50: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   69 |                                 }else if(info_ptr->pixel_depth == 24){
      |                                                  ^~
scripts/png2logo.c:81:40: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   81 |                 for(i = 0; i < info_ptr->height; i++)
      |                                        ^~
scripts/png2logo.c:83:51: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   83 |                         for(j = 0; j < ( (info_ptr->pixel_depth / 8) * info_ptr->width); j += (info_ptr->pixel_depth / 8) )
      |                                                   ^~
scripts/png2logo.c:83:80: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   83 |                         for(j = 0; j < ( (info_ptr->pixel_depth / 8) * info_ptr->width); j += (info_ptr->pixel_depth / 8) )
      |                                                                                ^~
scripts/png2logo.c:83:104: error: invalid use of incomplete typedef ‘png_info’ {aka ‘struct png_info_def’}
   83 |                         for(j = 0; j < ( (info_ptr->pixel_depth / 8) * info_ptr->width); j += (info_ptr->pixel_depth / 8) )
      |                                                                                                        ^~
scripts/png2logo.c:51:22: warning: unused variable ‘pixel_num’ [-Wunused-variable]
   51 |         unsigned int pixel_num = info_ptr->height * info_ptr->width;
      |                      ^~~~~~~~~
make[1]: *** [scripts/Makefile.host:118: scripts/png2logo] Error 1
make: *** [Makefile:518: scripts] Error 2

解法如下：

info_ptr->width => png_get_image_width(png_ptr, info_ptr)
info_ptr->height => png_get_image_height(png_ptr, info_ptr)
info_ptr->pixel_depth => png_get_bit_depth(png_ptr, info_ptr)