DEFINITION MODULE GR_Primitives;

    (*
    **  Author : Peter Jardine
    **
    **  Version:
    **  1.0      9 Mar 92   New file - based on the work of 
    **                      Michael McCarthy & John Pfitzner,
    **                      CSP-960 Project, Semester 2, 1991
    **
    **
    **  A GPM Modula-2 graphics library module.
    **
    *)

PROCEDURE ClearDisplay;
    (*
    **  Clear fill the screen with specified background colour. If clipping
    **  is on, clear fills only clipping rectangle.
    *)

PROCEDURE Bezier(nCtrl : CARDINAL; VAR col, row : ARRAY OF INTEGER);
PROCEDURE BezierNDC(nCtrl : CARDINAL; VAR x, y : ARRAY OF REAL);
    (*
    **  Draw a Bezier curve between the first and last points in the array
    **  of coordinates, using the intermediate points as the control points.
    **  nCtrl must be >= 1.  VAR parameters are used for efficiency.  These 
    **  routines will not alter the contents of the arrays.
    *)

PROCEDURE Circle(radius : CARDINAL; colCentre, rowCentre : INTEGER);
PROCEDURE CircleNDC(radius, xCentre, yCentre : REAL);
    (*
    **  Draw a "circle" of given radius, and centre. This is faster than
    **  the routine below.  Circles will appear elliptical unless drawn in a 
    **  square aspect mode (MaxXAspect or MaxYAspect).
    *)

PROCEDURE Ellipse(col1, row1, col2, row2 : INTEGER);
PROCEDURE EllipseNDC(x1, y1, x2, y2 : REAL);
    (*
    **  Draw an ellipse bounded by the rectangle (col1, row1), (col2, row2).
    *)

PROCEDURE FillArea(col, row : INTEGER);
PROCEDURE FillNDCArea(x, y : REAL);
    (*
    **  Fill the area containing the seed coordinate.
    *)

PROCEDURE Line(col1, row1, col2, row2 : INTEGER);
PROCEDURE LineNDC(x1, y1, x2, y2 : REAL);
    (*
    **  Draw a line between (col1,row1) & (col2,row2)
    *)

PROCEDURE PolyLine(nPoints : CARDINAL; VAR col, row : ARRAY OF INTEGER);
PROCEDURE PolyNDCLine(nPoints : CARDINAL; VAR x, y : ARRAY OF REAL);
    (*
    **  Draw polyline whose coordinates are stored in the arrays col and
    **  row. This is equivalent to npoints calls to Line of the form
    **  Line(col[i],row[i], col[i+1],row[i+1]).    VAR parameters are used for 
    **  efficiency.  These routines will not alter the contents of the arrays. 
    *) 

PROCEDURE WritePixel(col, row : INTEGER);
PROCEDURE WriteNDCPixel(x, y : REAL );
    (*
    **  Write a pixel at coordinates (col,row)
    *)

PROCEDURE ReadPixel(col, row : INTEGER; VAR colour : CARDINAL);
PROCEDURE ReadNDCRGBPixel(x, y : REAL; VAR red, green, blue : REAL);
    (*
    **  Returns the colour value of a specified pixel
    *)

END GR_Primitives.