Class KaliCanvas

java.lang.Object
   |
   +----KaliCanvas

class KaliCanvas

extends Object

(It might be more efficient to have the Panorama object make the graphics calls directly, but for now we try it this way.)

Coordinate systems:

Kali uses 3 different coordinate systems for the image in the DrawPanel:

Raw Screen Coordinates

This is the original screen coordinate system of the drawing area, which goes from (0,0) in the upper left to (screenWidth, screenHeight) in the lower right (in pixels). Y increases DOWN in this system.

Mouse events happen in this coordinate system.

Screen Coordinates

This system is the result of translating the raw screen system so that (0,0) is at the center of the screen; so it goes from (-screenWidth/2, -screenHeight/2) in the upper left to (screenWidth/2, screenHeight/2) in the lower right. Y increases DOWN in this system too.

Drawing happens in this coordinate system; the KaliCanvas.setGraphics() method calls g.translate() to move the Graphics object's origin from the upper left (the default) to the center of the screen. Also, the translation computations in the Panorama object happen in this system.

Internal Coordinates

This system goes from (-internalWidth, internalHeight) in the upper left to (internalWidth, -internalHeight) in the lower right; so (0,0) is at the center of the screen. Y increases UP in this system.

The coordinates of drawn segments are stored in this system. Also, the Panorama object does some of the group action math (reflection and rotation) in this system.

Also, in the future, scaling and translation may be implemented by transforming this system.

See Also:

Panorama, DrawPanel

KaliCanvas()

drawSegment(Segment, Color)

Draw a single line segment.

internalToScreen(DVector)

Convert internal coordinates to screen coordinates.

rawScreenToInternal(int, int)

Convert raw screen coordinates to internal coordinates.

setGraphics(Graphics)

Set the graphics context for future drawing; this results in a new screen coordinate system being computed based on the current size of this graphics context.

  public KaliCanvas()

  public DVector rawScreenToInternal(int x,
                                     int y)

Convert raw screen coordinates to internal coordinates.

  public DVector internalToScreen(DVector v)

Convert internal coordinates to screen coordinates.

  public void setGraphics(Graphics g)

Set the graphics context for future drawing; this results in a new screen coordinate system being computed based on the current size of this graphics context.

  public void drawSegment(Segment s,
                          Color c)

Draw a single line segment.

The Geometry Center Home Page

Author: Mark Phillips
Comments to: webmaster@geom.umn.edu
Created: Sep 16 1996 --- Last modified: Sep 18 1996