The Mjølner System: Bifrost

Bifrost is an interactive object-oriented graphics system based on the Stencil & Paint imaging model. Bifrost models computer graphics images by abstracting the geometric and color properties of graphical objects. The important new concept introduced in Bifrost is that there is one basic drawing primitive, the graphical object. The graphical object unite interaction, graphics modelling and graphics context. Bifrost includes extensive support for various kinds of interaction: interactive creation, reshaping, translation, scaling, and rotation of graphical objects. The object-oriented approach makes extensibility and tailorability a simple task, and facilitates object-oriented drawing applications. One of the main goals of the development of Bifrost was to make the graphics system independent of underlying graphics and hardware systems.

Important concepts of Bifrost

Canvas: Representation of the drawing surface, and the connection between the display device and Bifrost. The canvas contains a picture, and all graphics shown in the canvas must be in the canvas picture.
Shape: The shape describes the outline of the image, you want to display, A shape is described by menas of segments. A segment is either a straight line segment or a spline segment. Spline segments are used to describe curves. The shape is analogous to the stencil in the Stencil & Paint imaging model.
Paint: The paint of Bifrost represent the color or raster to be pushed through a shape, thus making the corresponding graphical object appear on a canvas. The Paint can be simple solid colors using a predefined name of the color or relative to some color space, e.g. RGB, HSV, CMY. Tiles and rasters, e.g. scanned images, can also be used as paint.
Graphical Object: The graphical object concept constitute the composition of two concepts shape and paint. The graphical object is the smallest unit that can be displayed on a canvas.
Picture: A picture is a collection of graphical objects, and realizes the concept of graphics modelling. The graphical object is the smallest possible entity that can be drawn, and is complete in the sense, that it contains all necessary information about how the graphical object appears on the canvas, and is therefore independent of any other graphical objects in a picture.

The basic imaging model of Bifrost is thus very simple: define a shape that represents the outline of the object you want to draw, select a paint as the color for the object, construct a graphical object with the shape and paint just defined, and draw the object in a canvas, i.e. insert the graphical object into the canvas picture. If the object must have several different colors the object must be split into more graphical objects and assembled in a picture. The picture is a graphical object itself, and can thus be drawn in a canvas.

Example

The following complete program is a small example showing how to make a simple Shape consisting of Line- and SplineSegments, and then filling the Shape with a pink SolidColor. The resulting graphical object can later be reshaped and moved.

[myShape demo screen dump]

ORIGIN '~beta/bifrost/Bifrost';
INCLUDE '~beta/bifrost/private/Impl/debug';
INCLUDE '~beta/bifrost/ColorNames';

-- program: descriptor --
bifrost
(# theWindow: @window
     (# theCanvas: @BifrostCanvas
          (# aGO: @GraphicalObject;
             aSolidColor: @SolidColor;
             
             myShape: @Shape
               (#
               do (100,100) -> open;
                  (100,150) -> lineto;
                  (125,200) -> splineto;
                  (200,170) -> splineto;
                  (195,100) -> splineto;
                  close;
               #);
             
             eventhandler::
               (# 
                  onOpen::
                    (#
                    do aSolidColor.init;
                       pink -> aSolidColor.name;
                       aGO.init;
                       myShape -> aGO.setShape;
                       aSolidColor[]-> aGO.setpaint;
                       aGO[] -> draw;
                       aGO[] -> hilite;
                    #);
                  onMouseDown::
                  close;
               #);
             
             eventhandler::
               (# 
                  onOpen::
                    (#
                    do aSolidColor.init;
                       pink -> aSolidColor.name;
                       aGO.init;
                       myShape -> aGO.setShape;
                       aSolidColor[]-> aGO.setpaint;
                       aGO[] -> draw;
                       aGO[] -> hilite;
                    #);
                  onMouseDown::
                    (# exactPos: ^point;
                    do mousePos -> DeviceToCanvas -> mousePos;
                       (aGO[], mousePos)-> HitControl -> exactpos[];
                       (if exactpos[] <> NONE then
                           aGO[] -> unhilite;
                           (aGO[], exactPos, NoModifier)
                             -> interactiveReshape;
                           aGO[] -> hilite;
                        else
                           (if (theCanvas[],mousePos) -> aGO.containsPoint then
                               aGO[] -> unhilite;
                               (aGO[], mousePos, NoModifier)
                                 -> interactiveMove;
                               aGO[] -> hilite;
                           if);
                       if);
                    #);
                  onKeyDown:: (# do terminate #);
               #);
             open::
               (# do theWindow.size->size; #);
          #);
        open::
          (# do (300,300)->size; theCanvas.open; #);
     #);
do theWindow.open;
#)

More Information

For further information, see

Mjølner System: Bifrost - Tutorial.
Mjølner System: Bifrost - Reference Manual.

Bifrost is the luminous bridge, the rainbow, that leads from Midgaard to Asgaard. Midgaard is the place where the human beings live. Asgaard is the habitat of the gods in the middle of the world.