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MANUAL.md

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Manual for: OCamlSDL2

Initialisation

let () =
  Sdl.init [`VIDEO]

Initialises the SDL2 library, for use with something visible on screen.

Prefixed, or Prefixless?

If you prefer to use the modules, without the 'Sdl' prefix, you can add this open, at the beginning of your file:

open Sdl

Render, and Renderers

A possibility to draw on screen, inside the window, is to use a renderer with the render module.

We can initialise a window, and a renderer, with the function:

  Sdlrender.create_window_and_renderer ~width ~height ~flags:[]

Here is an example, which will draw four points in a window, with a renderer, and the render module:

let () =
  Sdl.init [`VIDEO];

  let width, height = (320, 240) in

  let window, renderer =
    Sdlrender.create_window_and_renderer ~width ~height ~flags:[]
  in

  Sdlrender.set_draw_color renderer ~rgb:(0,255,255) ~a:255;
  Sdlrender.clear renderer;

  Sdlrender.set_draw_color renderer ~rgb:(0,0,127) ~a:255;
  Sdlrender.draw_point renderer (120, 120);
  Sdlrender.draw_point renderer (122, 120);
  Sdlrender.draw_point renderer (124, 120);
  Sdlrender.draw_point renderer (126, 120);

  Sdlrender.render_present renderer;
  Sdltimer.delay 6000;

  Sdl.quit ();
;;

Here are some explanations about how this example works:

  • first we have to fill the background with a color, this operation is achieved with two function calls,

    the first one, defines the color,

  Sdlrender.set_draw_color

and the second one, requests the renderer to erase the contents of the window, with this selected color.

  Sdlrender.clear renderer;

this is usually what we do, if we want to display, a game, or any other kind of content that we want to animate (in case the background doesn't fill all the window, inside the drawing area).

  • After we draw four points with the function below:
  Sdlrender.draw_point

Again we have to define a color first, as if we would choose a color pen:

  Sdlrender.set_draw_color

While painting, the primary colors are: cyan, magenta, and yellow. But with a screen, the primary colors are: red, green, and blue.

Most often these three colors have to be defined in this order. With screen colors, we create a yellow color, by mixing red and green. And leaving blue to zero, or any value close to zero.

In the above example, we select a turquoise color, for the background, with:

  (0,255,255)

And a dark-blue, for the four points, with:

  (0,0,127)

At the end of all the draw request elements, we should call the renderer with the render_present function, to make the drawing visible on screen:

  Sdlrender.render_present renderer;

Then we ask to wait 6 seconds:

  Sdltimer.delay 6000;

This function uses milliseconds, to make pauses smaller than one second (so that we can make smooth animations).

The equivalent of 6 seconds, is 6000 milliseconds.

Then we can quit if we have finished with what we want to display:

  Sdl.quit ()

Sprites Elements

If you want to create a game, or an animation, with real painting, you can take a picture of your painting with a smartphone (if you don't have one, you can ask a friend). Small pieces of images, that are used to display, are often called "sprites" (or "tiles" for background elements.)

The prefered image-file format for use with sdl-2 is the ".bmp" format.

In the console, an easy way to convert a ".png" or ".jpg" image to ".bmp", is to use a command from image-magick:

$ convert my_sprite.png my_sprite.bmp