# Module Graphics

    module Graphics: sig .. end

Machine-independent graphics primitives.

    exception Graphic_failure of string

Raised by the functions below when they encounter an error.

## Initializations

    val open_graph : string -> unit

Show the graphics window or switch the screen to graphic mode. The graphics window is cleared and the current point is set to (0, 0). The string argument is used to pass optional information on the desired graphics mode, the graphics window size, and so on. Its interpretation is implementation-dependent. If the empty string is given, a sensible default is selected.

    val close_graph : unit -> unit

Delete the graphics window or switch the screen back to text mode.

    val set_window_title : string -> unit

Set the title of the graphics window.

    val resize_window : int -> int -> unit

Resize and erase the graphics window.

    val clear_graph : unit -> unit

Erase the graphics window.

    val size_x : unit -> int

See `Graphics.size_y`.

    val size_y : unit -> int

Return the size of the graphics window. Coordinates of the screen pixels range over `0 .. size_x()-1` and `0 .. size_y()-1`. Drawings outside of this rectangle are clipped, without causing an error. The origin (0,0) is at the lower left corner. Some implementation (e.g. X Windows) represent coordinates by 16-bit integers, hence wrong clipping may occur with coordinates below `-32768` or above `32676`.

## Colors

    type color = int

A color is specified by its R, G, B components. Each component is in the range `0..255`. The three components are packed in an `int`: `0xRRGGBB`, where `RR` are the two hexadecimal digits for the red component, `GG` for the green component, `BB` for the blue component.

    val rgb : int -> int -> int -> color

`rgb r g b` returns the integer encoding the color with red component `r`, green component `g`, and blue component `b`. `r`, `g` and `b` are in the range `0..255`.

    val set_color : color -> unit

Set the current drawing color.

    val background : color

See `Graphics.foreground`.

    val foreground : color

Default background and foreground colors (usually, either black foreground on a white background or white foreground on a black background). `Graphics.clear_graph` fills the screen with the `background` color. The initial drawing color is `foreground`.

Some predefined colors

    val black : color

    val white : color

    val red : color

    val green : color

    val blue : color

    val yellow : color

    val cyan : color

    val magenta : color

## Point and line drawing

    val plot : int -> int -> unit

Plot the given point with the current drawing color.

    val plots : (int * int) array -> unit

Plot the given points with the current drawing color.

    val point_color : int -> int -> color

Return the color of the given point in the backing store (see "Double buffering" below).

    val moveto : int -> int -> unit

Position the current point.

    val rmoveto : int -> int -> unit

`rmoveto dx dy` translates the current point by the given vector.

    val current_x : unit -> int

Return the abscissa of the current point.

    val current_y : unit -> int

Return the ordinate of the current point.

    val current_point : unit -> int * int

Return the position of the current point.

    val lineto : int -> int -> unit

Draw a line with endpoints the current point and the given point, and move the current point to the given point.

    val rlineto : int -> int -> unit

Draw a line with endpoints the current point and the current point translated of the given vector, and move the current point to this point.

    val curveto : int * int -> int * int -> int * int -> unit

`curveto b c d` draws a cubic Bezier curve starting from the current point to point `d`, with control points `b` and `c`, and moves the current point to `d`.

    val draw_rect : int -> int -> int -> int -> unit

`draw_rect x y w h` draws the rectangle with lower left corner at `x,y`, width `w` and height `h`. The current point is unchanged. Raise `Invalid_argument` if `w` or `h` is negative.

    val draw_poly_line : (int * int) array -> unit

`draw_poly_line points` draws the line that joins the points given by the array argument. The array contains the coordinates of the vertices of the polygonal line, which need not be closed. The current point is unchanged.

    val draw_poly : (int * int) array -> unit

`draw_poly polygon` draws the given polygon. The array contains the coordinates of the vertices of the polygon. The current point is unchanged.

    val draw_segments : (int * int * int * int) array -> unit

`draw_segments segments` draws the segments given in the array argument. Each segment is specified as a quadruple `(x0, y0, x1, y1)` where `(x0, y0)` and `(x1, y1)` are the coordinates of the end points of the segment. The current point is unchanged.

    val draw_arc : int -> int -> int -> int -> int -> int -> unit

`draw_arc x y rx ry a1 a2` draws an elliptical arc with center `x,y`, horizontal radius `rx`, vertical radius `ry`, from angle `a1` to angle `a2` (in degrees). The current point is unchanged. Raise `Invalid_argument` if `rx` or `ry` is negative.

    val draw_ellipse : int -> int -> int -> int -> unit

`draw_ellipse x y rx ry` draws an ellipse with center `x,y`, horizontal radius `rx` and vertical radius `ry`. The current point is unchanged. Raise `Invalid_argument` if `rx` or `ry` is negative.

    val draw_circle : int -> int -> int -> unit

`draw_circle x y r` draws a circle with center `x,y` and radius `r`. The current point is unchanged. Raise `Invalid_argument` if `r` is negative.

    val set_line_width : int -> unit

Set the width of points and lines drawn with the functions above. Under X Windows, `set_line_width 0` selects a width of 1 pixel and a faster, but less precise drawing algorithm than the one used when `set_line_width 1` is specified. Raise `Invalid_argument` if the argument is negative.

## Text drawing

    val draw_char : char -> unit

See `Graphics.draw_string`.

    val draw_string : string -> unit

Draw a character or a character string with lower left corner at current position. After drawing, the current position is set to the lower right corner of the text drawn.

    val set_font : string -> unit

Set the font used for drawing text. The interpretation of the argument to `set_font` is implementation-dependent.

    val set_text_size : int -> unit

Set the character size used for drawing text. The interpretation of the argument to `set_text_size` is implementation-dependent.

    val text_size : string -> int * int

Return the dimensions of the given text, if it were drawn with the current font and size.

## Filling

    val fill_rect : int -> int -> int -> int -> unit

`fill_rect x y w h` fills the rectangle with lower left corner at `x,y`, width `w` and height `h`, with the current color. Raise `Invalid_argument` if `w` or `h` is negative.

    val fill_poly : (int * int) array -> unit

Fill the given polygon with the current color. The array contains the coordinates of the vertices of the polygon.

    val fill_arc : int -> int -> int -> int -> int -> int -> unit

Fill an elliptical pie slice with the current color. The parameters are the same as for `Graphics.draw_arc`.

    val fill_ellipse : int -> int -> int -> int -> unit

Fill an ellipse with the current color. The parameters are the same as for `Graphics.draw_ellipse`.

    val fill_circle : int -> int -> int -> unit

Fill a circle with the current color. The parameters are the same as for `Graphics.draw_circle`.

## Images

    type image

The abstract type for images, in internal representation. Externally, images are represented as matrices of colors. Images are bound to the current graphics window and should not be reused after closing this graphics window with `Graphics.close_graph`.

    val transp : color

In matrices of colors, this color represent a 'transparent' point: when drawing the corresponding image, all pixels on the screen corresponding to a transparent pixel in the image will not be modified, while other points will be set to the color of the corresponding point in the image. This allows superimposing an image over an existing background.

    val make_image : color array array -> image

Convert the given color matrix to an image. Each sub-array represents one horizontal line. All sub-arrays must have the same length; otherwise, exception `Graphic_failure` is raised.

    val dump_image : image -> color array array

Convert an image to a color matrix.

    val draw_image : image -> int -> int -> unit

Draw the given image with lower left corner at the given point.

    val get_image : int -> int -> int -> int -> image

Capture the contents of a rectangle on the screen as an image. The parameters are the same as for `Graphics.fill_rect`.

    val create_image : int -> int -> image

`create_image w h` returns a new image `w` pixels wide and `h` pixels tall, to be used in conjunction with `blit_image`. The initial image contents are random, except that no point is transparent.

    val blit_image : image -> int -> int -> unit

`blit_image img x y` copies screen pixels into the image `img`, modifying `img` in-place. The pixels copied are those inside the rectangle with lower left corner at `x,y`, and width and height equal to those of the image. Pixels that were transparent in `img` are left unchanged.

## Mouse and keyboard events

    type status = {

`` | `mouse_x : `int`;` | `(*` | X coordinate of the mouse | `*)`
`` | `mouse_y : `int`;` | `(*` | Y coordinate of the mouse | `*)`
`` | `button : `bool`;` | `(*` | true if a mouse button is pressed | `*)`
`` | `keypressed : `bool`;` | `(*` | true if a key has been pressed | `*)`
`` | `key : `char`;` | `(*` | the character for the key pressed | `*)`

}

To report events.

    type event =

`|` | `Button_down` | `(*` | A mouse button is pressed | `*)`
`|` | `Button_up` | `(*` | A mouse button is released | `*)`
`|` | `Key_pressed` | `(*` | A key is pressed | `*)`
`|` | `Mouse_motion` | `(*` | The mouse is moved | `*)`
`|` | `Poll` | `(*` | Don't wait; return immediately | `*)`

To specify events to wait for.

    val wait_next_event : event list -> status

Wait until one of the events specified in the given event list occurs, and return the status of the mouse and keyboard at that time. If `Poll` is given in the event list, return immediately with the current status. If the mouse cursor is outside of the graphics window, the `mouse_x` and `mouse_y` fields of the event are outside the range `0..size_x()-1, 0..size_y()-1`. Keypresses are queued, and dequeued one by one when the `Key_pressed` event is specified and the `Poll` event is not specified.

    val loop_at_exit : event list -> (status -> unit) -> unit

Loop before exiting the program, the list given as argument is the list of handlers and the events on which these handlers are called. To exit cleanly the loop, the handler should raise Exit. Any other exception will be propagated outside of the loop.

- Since 4.01

## Mouse and keyboard polling

    val mouse_pos : unit -> int * int

Return the position of the mouse cursor, relative to the graphics window. If the mouse cursor is outside of the graphics window, `mouse_pos()` returns a point outside of the range `0..size_x()-1, 0..size_y()-1`.

    val button_down : unit -> bool

Return `true` if the mouse button is pressed, `false` otherwise.

    val read_key : unit -> char

Wait for a key to be pressed, and return the corresponding character. Keypresses are queued.

    val key_pressed : unit -> bool

Return `true` if a keypress is available; that is, if `read_key` would not block.

## Sound

    val sound : int -> int -> unit

`sound freq dur` plays a sound at frequency `freq` (in hertz) for a duration `dur` (in milliseconds).

## Double buffering

    val auto_synchronize : bool -> unit

By default, drawing takes place both on the window displayed on screen, and in a memory area (the 'backing store'). The backing store image is used to re-paint the on-screen window when necessary.

To avoid flicker during animations, it is possible to turn off on-screen drawing, perform a number of drawing operations in the backing store only, then refresh the on-screen window explicitly.

`auto_synchronize false` turns on-screen drawing off. All subsequent drawing commands are performed on the backing store only.

`auto_synchronize true` refreshes the on-screen window from the backing store (as per `synchronize`), then turns on-screen drawing back on. All subsequent drawing commands are performed both on screen and in the backing store.

The default drawing mode corresponds to `auto_synchronize true`.

    val synchronize : unit -> unit

Synchronize the backing store and the on-screen window, by copying the contents of the backing store onto the graphics window.

    val display_mode : bool -> unit

Set display mode on or off. When turned on, drawings are done in the graphics window; when turned off, drawings do not affect the graphics window. This occurs independently of drawing into the backing store (see the function `Graphics.remember_mode` below). Default display mode is on.

    val remember_mode : bool -> unit

Set remember mode on or off. When turned on, drawings are done in the backing store; when turned off, the backing store is unaffected by drawings. This occurs independently of drawing onto the graphics window (see the function `Graphics.display_mode` above). Default remember mode is on.