3.2 Drawing Area

All the drawing is performed using a virtual brush. the brush has the following intrinsic characteristics:

1. A position relatively to the lower left corner of the drawing area. This position can be got/set using the Cartesian coordinate system as we as the Polar coordinate system.
2. An Orientation relatively to the horizontal orientation and counter clockwise. For the sake of simplicity, all the angles are expressed in “Degree”.

Its obvious that only one of these characteristics is sufficient to perform all kinds of drawing. However, combining both systems may simplify enormously some complex drawings.

type Color_Type is private;

This is the color type used to perform all the drawings. The type is a private type since the user has not to know the internals of the type to use it.

function RGB (R : Integer; G : Integer; B : Integer) return Color_Type;

This function cretes an RGB (Red Green Blue) color. All the given parameter are considered modulo 65536, the maximal value of a color composant.

IMPORTANT NOTE: All custom colors must be declared before the call to Create_Main_Window.

The library defines some predefined colors that may be used without calling RGB:

• Black
• Red
• Green
• Yello
• Blue
• Magenta
• Cyan
• Orange
• Pink
• Dark_Gray
• Gray
• Light_Gray
• White

All the routines below:

• are thread-safe, in the sence that the call to a routine is “atomic” to avoid interference between different tasks calling different routines.
• verify the existence of the graphical window and the drawing area and raise an error if on of themhas not been created.

procedure Clear_Drawing_Area;

This procedure “blanks' the drawing area.

procedure Set_Color (C : Color_Type);

This procedure sets the color of the virtual brush to C.

function Get_Color return Color_Type;

This function returns the current color of the virtual brush.

procedure Set_Thickness (T : Float);

This procedure sets the thickness of the virtual brush to T.

function Get_Thickness return Float;

This function returns the current thickness of the virtual brush.

procedure Set_Angle (Angle : Float);

This procedure sets the angle between the horizontal and the virtual brush orientation to Angle

function Get_Angle return Float;

This function returns the angle between the horizontal and the virtual brush orientation.

procedure Rotate (Angle : Float);

This procedure modifies the virtual brush orientation to Angle + Current_Orientation.

procedure Set_Position (X : Float; Y : Float);

This function sets the current Cartesian position of the virtual brush to (X,Y).

procedure Get_Position (X : out Float; Y : out Float);

This procedure gets the current Cartesian position of the virtual brush.

procedure Jump (Distance : Float);

This procedure jumps straight forward the given distance in the direction the virtual brush without drawing any line.

procedure Jump (X : Float; Y : Float);

Same as above but using the Cartesian coordinate.

procedure Line (Distance : Float);

This procedure jumps straight forward the given distance in the direction the virtual brush and draws a line between the start and the end points. The color, style and thickness of the line are specified using the appropriate routines.

procedure Line (X : Float; Y : Float);

Same as above but using the Cartesian coordinate.

procedure Line (X_Start  : Float;
                Y_Start  : Float;
                Distance : Float);

Same as above but start from (X_Start, Y_Start). At the end of execution, the virtual brush is located at the end of the drwn line.

procedure Line
  (X_Start : Float;
   Y_Start : Float;
   X_End   : Float;
   Y_End   : Float);

Same as above, but with the Cartesian destination.

procedure Point;

This procedure draws a point in the current position.

procedure Point (Center_X : Float; Center_Y : Float);

Same as above but with a custom position.

type X_Justification_Type is (Left, Center, Right);
type Y_Justification_Type is (Top, Center, Bottom);

These two enumeration types are used to align horizontally and vertically inserted text and images (see below).

procedure Insert_Image
  (File_Name       : String;
   Scale           : Float                := 1.0;
   X_Justification : X_Justification_Type := Center;
   Y_Justification : Y_Justification_Type := Center);

This procedure draws a graphic justified at the virtual brush's current location. This will draw any graphic that Gtk understands, including JPEG, GIF, BMP, PNG, PBM, TIFF, and perhaps some others.

IMPORTANT NOTE: If the given path to the image is a relative path, the image location is calculated relatively to the working directory.

procedure Insert_Text
  (Text            : String;
   Size            : Float                := 10.0;
   X_Justification : X_Justification_Type := Center;
   Y_Justification : Y_Justification_Type := Center);

This procedure draws a text string justified at the virtual brush's current location. The size is expressed in Pixels.

procedure Draw_Circle (Radius : Float);

This procedure draws a circle with radius Radius and with the center at the current position of the virtual brush.

procedure Draw_Circle
  (Center_X : Float;
   Center_Y : Float;
   Radius   : Float);

Same as above but the position of the center is given.

procedure Fill_Circle (Radius : Float);

This procedure fills a circle with radius Radius and with the center at the current position of the virtual brush. Note that the actual radius of the filled circle is Radius - 1 pixel.

procedure Fill_Circle
  (Center_X : Float;
   Center_Y : Float;
   Radius   : Float);

Same as above but the position of the center is given.

procedure Draw_Rectangle
  (First_X : Float;
   First_Y : Float;
   Width   : Float;
   Height  : Float);

This procedure draws a rectangle having the specified bottom left edge.

procedure Fill_Rectangle
  (First_X : Float;
   First_Y : Float;
   Width   : Float;
   Height  : Float);

This procedure fills a rectangle having the specified bottom left edge edges. Note that the actual sizes of the filled rectangle is reduced by 1 pixel.

type Float_Array is array (Positive range <>) of Float;

This type defines an array of Float. It must be instantiated with tha actual size.

procedure Draw_Polygon (Edges : Float_Array);

This procedure draws a polygon by linking the given edges. The array must be in the form (X1, Y1, X2, Y2..., Xn, Yn). There fore its length must be even. If the length of 'Edges' is odd, raise Constraint_Error.

procedure Fill_Polygon (Edges : Float_Array);

This procedure fills a polygon as it would have been drawn by the subprogram above.

procedure Rafresh;

This procedure redraws the drawing area.

procedure Get_Mouse_Pointer
  (X      : out Float;
   Y      : out Float;
   Button : out Natural);

This procedure waits for a mouse button action and stores the mouse pointer coordinate in X and Y and the mouse button used to do the action. If the user closes the windows before giving a mouse click, Lost_Main_Window will be raised.