Example using Cairo with SDL

[aryx]

I would like to draw shapes on a screen, but I also need to rotate them, scale them, etc. and it looks like SDL by itself does not provide this functionality. I know Cairo which can do all of that but I need some toy example showing how to mix cairo and SDL code together.

For reference, here is some example showing how to mix Cairo with the Graphics library: https://github.com/Chris00/ocaml-cairo/blob/master/examples/graphics_demo.ml

Would be great to have something similar but for SDL! That way, as advertised here: https://www.cairographics.org/SDL/ we can mix the best of both worlds (cairo for advanced drawing and SDL for cross-platform game platform).

[fccm]

Something like this? https://gist.github.com/fccm/f537701f7da8a413b14c25feb93bac4b

run it with:

ocaml -I ../../OCamlSDL2/src sdl2.cma sdl2-ba.cma -I $(ocamlfind query cairo2) cairo.cma ex_cairo.ml

It seems quite slow though, you will maybe be more lucky wrapping the SDL2_gfx lib:

/usr/lib/libSDL2_gfx.so
/usr/include/SDL2/SDL2_gfxPrimitives.h

You can take example of the "accompanying libraries":

• https://github.com/fccm/OCamlSDL2_TTF
• https://github.com/fccm/OCamlSDL2_Image
• https://github.com/fccm/OCamlSDL2_Mixer
• https://github.com/fccm/OCamlSDL2_Net

[fccm]

I just made a template bindings for the SDL2_gfx lib:

• https://github.com/fccm/OCamlSDL2_Gfx

You can easily add the functions you need.

[aryx]

Merci beaucoup florent!

In the end someone on discuss.ocaml.org answered my question via some existing code he wrote: https://discuss.ocaml.org/t/ocaml-native-library-to-draw-scale-rotate-shapes-on-screen/6706/10?u=aryx and even proposed a faster implementation using Cairo.Image.create_for_data32 which avoids some extra copy. It's very fast. https://github.com/igarnier/vplot/blob/master/lib/display.ml

I think you should add a similar example in your SDL binding; it's a big limitation of SDL do not be able to rotate or have powerful drawing like in Cairo, and the ability to mix easily cairo and SDL through Cairo.Image.create_for_data32 is very nice.

[fccm]

Of course you do can scale and rotate with SDL2!

In the example I provided please have a look at lines 95 and 96, the parameter named angle is the angle to rotate, and I even put a comment (* rotate *).

Use the function Render.copyEx to rotate and scale: https://fccm.github.io/OCamlSDL2/Sdlrender.html#VALcopyEx

I also put a comment at line 92 to explain how to scale:

    (* Use rectangles of different width and height to scale *)

[aryx]

Oh thx, but this seems still a bit more tedious than the draw_rect, draw_ellipse, draw_line, draw_text that Cairo provides that can be rotated/scaled/translated in many ways.

[fccm]

Then switching to ocaml-sfml could be a good choice. It provides all these functions that you need in a native way.