Add CMake build script to the project

[tamasmeszaros]

Hello there! I'm sending this PR on behalf of the PrusaSlicer team. We are using nanosvg in our software and having trouble with symbol duplication since wxWidgets also started using this library.

Since both our team and the wxWidgets team is using CMake, I've written the CMake build and install scripts to be able to import the library in both projects without duplication issues.

I've also added a short extension to the readme file to address the new integration method.

I know that this goes somewhat against the philosophy of the library to be simple to integrate and the examples already use a different build system but this is the solution we could provide quickly and believe it would have the most widespread acceptance in the community.

[tamasmeszaros]

Related discussion wxWidgets/wxWidgets#22393

[memononen]

@tamasmeszaros I'm willing to merge this if I can summon you to fix the cmake issues in the future :) Would that work for you?

[tamasmeszaros]

Hi @memononen! Thank you, I can handle it for you.

[tamasmeszaros]

It would be good to consider the versioning before merging the PR. What concerns me is this line b21ebe0#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20aR25

Which assumes that this library is at version 1.0 and any matching or newer version is usable as a drop-in. This versioning thing could be omitted but I think it's safer to leave it there and agree on a version now, and maybe even make the compatibility somewhat stricter, (e.g. only matching major versions are compatible). But if you are confident that the library is now finished and will not change much in the future, it's not that big of a deal.

[memononen]

Good point about versions. With the time i have to maintain this project (which is close to zero), it's quite hard to maintain releases. I'm fine with 1.0, and if that allows us to later differentiate incompatible versions, that is great.

[bubnikv]

Great, thanks to all involved!

[akien-mga]

With this change, it's no longer possible to include nanosvgrast.h after including nanosvg.h as it leads to duplicate symbols:

$ cat << EOF > nanosvg.cc
#include "stdio.h"
#include "string.h"
#include "math.h"
#define NANOSVG_ALL_COLOR_KEYWORDS
#define NANOSVG_IMPLEMENTATION
#include "nanosvg.h"
#define NANOSVGRAST_IMPLEMENTATION
#include "nanosvgrast.h"
EOF

$ g++ nanosvg.cc
In file included from nanosvgrast.h:28,
                 from nanosvg.cc:8:
nanosvg.h:219:12: error: redefinition of ‘int nsvg__isspace(char)’
  219 | static int nsvg__isspace(char c)
      |            ^~~~~~~~~~~~~
In file included from nanosvg.cc:6:
nanosvg.h:219:12: note: ‘int nsvg__isspace(char)’ previously defined here
  219 | static int nsvg__isspace(char c)
      |            ^~~~~~~~~~~~~
nanosvg.h:224:12: error: redefinition of ‘int nsvg__isdigit(char)’
  224 | static int nsvg__isdigit(char c)
      |            ^~~~~~~~~~~~~
nanosvg.h:224:12: note: ‘int nsvg__isdigit(char)’ previously defined here
  224 | static int nsvg__isdigit(char c)
      |            ^~~~~~~~~~~~~
nanosvg.h:229:26: error: redefinition of ‘float nsvg__minf(float, float)’
  229 | static NSVG_INLINE float nsvg__minf(float a, float b) { return a < b ? a : b; }
      |                          ^~~~~~~~~~
nanosvg.h:229:26: note: ‘float nsvg__minf(float, float)’ previously defined here
  229 | static NSVG_INLINE float nsvg__minf(float a, float b) { return a < b ? a : b; }
      |                          ^~~~~~~~~~
nanosvg.h:230:26: error: redefinition of ‘float nsvg__maxf(float, float)’
  230 | static NSVG_INLINE float nsvg__maxf(float a, float b) { return a > b ? a : b; }
      |                          ^~~~~~~~~~
nanosvg.h:230:26: note: ‘float nsvg__maxf(float, float)’ previously defined here
  230 | static NSVG_INLINE float nsvg__maxf(float a, float b) { return a > b ? a : b; }
      |                          ^~~~~~~~~~
...

and dozens more errors.

[memononen]

That include should not be there, my bad reviewing it. @tamasmeszaros would you mind making another PR fixing that?

[tamasmeszaros]

Yes, but I would not remove the include but rather extend the include guards for the whole files for nanosvg.h and nanosvgrast.h.

See #215
I've also added a bonus PR #216 with a CMake build script for the examples. Use it if you like it :)