A canvas is a two-dimensional medium on which morphs are drawn in a device-independent manner. Canvases keep track of the origin and clipping rectangle, as well as the underlying drawing medium (such as a window, pixmap, or postscript script).

Subclasses must implement (at least) the following methods:
* Drawing:
#fillOval:color:borderWidth:borderColor:
#frameAndFillRectangle:fillColor:borderWidth:borderColor:
#drawPolygon:color:borderWidth:borderColor:
#image:at:sourceRect:rule:
#stencil:at:sourceRect:rule:
#line:to:width:color:
#paragraph:bounds:color:
#text:bounds:font:color:
* Support
#clipBy:during:
#translateBy:during:
#translateBy:clippingTo:during:
#transformBy:clippingTo:during:

	accessing
	clipRect contentsOfArea: contentsOfArea:into: depth extent form origin shadowColor shadowColor:

	converting
	asAlphaBlendingCanvas: asShadowDrawingCanvas asShadowDrawingCanvas:

	copying
	copy copyClipRect:

	drawing
	fillColor: line:to:brushForm: line:to:color: line:to:width:color: line:to:width:color:dashLength:secondColor:secondDashLength:startingOffset: line:to:width:color:stepWidth:secondWidth:secondColor:secondStepWidth: paragraph2:bounds:color: paragraph:bounds:color: point:color: render: text:at:font:color: text:bounds:font:color:

	drawing-general
	draw: drawMorph: fullDraw: fullDrawMorph: roundCornersOf:during:

	drawing-images
	drawImage:at: drawImage:at:sourceRect: paintImage:at: paintImage:at:sourceRect: stencil:at:color: stencil:at:sourceRect:color: translucentImage:at: translucentImage:at:sourceRect:

	drawing-obsolete
	image:at: image:at:rule: imageWithOpaqueWhite:at:

	drawing-ovals
	fillOval:color: fillOval:color:borderWidth:borderColor: fillOval:fillStyle: fillOval:fillStyle:borderWidth:borderColor: frameOval:color: frameOval:width:color:

	drawing-polygons
	drawPolygon:color:borderWidth:borderColor: drawPolygon:fillStyle: drawPolygon:fillStyle:borderWidth:borderColor:

	drawing-rectangles
	fillRectangle:color: fillRectangle:fillStyle: fillRectangle:fillStyle:borderStyle: frameAndFillRectangle:fillColor:borderWidth:borderColor: frameAndFillRectangle:fillColor:borderWidth:topLeftColor:bottomRightColor: frameRectangle:color: frameRectangle:width:color:

	drawing-support
	cache:using:during: clipBy:during: preserveStateDuring: transformBy:clippingTo:during: transformBy:clippingTo:during:smoothing: translateBy:during: translateTo:clippingTo:during:

	initialization
	finish flush reset

	other
	flushDisplay forceToScreen: translateBy:clippingTo:during:

	private
	image:at:sourceRect:rule: image:at:sourceRect:rule:alpha:

	testing
	doesRoundedCorners isBalloonCanvas isShadowDrawing isVisible: seesNothingOutside:

	Nebraska/embeddedWorlds	top
	displayIsFullyUpdated
	transform2By:clippingTo:during:smoothing: an attempt to use #displayInterpolatedOn: instead of WarpBlt.

	accessing	top
	clipRect Return the currently active clipping rectangle
	contentsOfArea: Return the contents of the given area
	contentsOfArea:into: Return the contents of the given area
	depth
	extent Return the physical extent of the output device
	form
	origin Return the current origin for drawing operations
	shadowColor Return the current override color or nil if no such color exists
	shadowColor: Set a shadow color. If set this color overrides any client-supplied color.

	converting	top
	asAlphaBlendingCanvas:
	asShadowDrawingCanvas
	asShadowDrawingCanvas:

	copying	top
	copy Answer another instance just like the receiver. Subclasses typically override this method; they typically do not override shallowCopy.
	copyClipRect:

	drawing	top
	fillColor: Fill the receiver with the given color. Note: This method should be named differently since it is intended to fill the background and thus fills even if the color is transparent
	line:to:brushForm: Obsolete - will be removed in the future
	line:to:color:
	line:to:width:color: Draw a line using the given width and color
	line:to:width:color:dashLength:secondColor:secondDashLength:startingOffset: Draw a line using the given width, colors and dash lengths. Originally written by Stephan Rudlof; tweaked by Dan Ingalls to use startingOffset for sliding offset as in 'ants' animations. Returns the sum of the starting offset and the length of this line.
	line:to:width:color:stepWidth:secondWidth:secondColor:secondStepWidth: Draw a line using the given width, colors and steps; both steps can have different stepWidths (firstStep, secondStep), draw widths and colors.
	paragraph2:bounds:color:
	paragraph:bounds:color: Draw the given paragraph
	point:color: Obsolete - will be removed in the future
	render: Do some 3D operations with the object if possible
	text:at:font:color:
	text:bounds:font:color: Draw the given string in the given font and color clipped to the given rectangle. If the font is nil, the default font is used.

	drawing-general	top
	draw:
	drawMorph:
	fullDraw:
	fullDrawMorph:
	roundCornersOf:during:

	drawing-images	top
	drawImage:at: Draw the given Form, which is assumed to be a Form or ColorForm
	drawImage:at:sourceRect: Draw the given form.
	paintImage:at: Draw the given Form, which is assumed to be a Form or ColorForm following the convention that zero is the transparent pixel value.
	paintImage:at:sourceRect: Draw the given Form, which is assumed to be a Form or ColorForm following the convention that zero is the transparent pixel value.
	stencil:at:color: Flood this canvas with aColor wherever stencilForm has non-zero pixels
	stencil:at:sourceRect:color: Flood this canvas with aColor wherever stencilForm has non-zero pixels
	translucentImage:at: Draw a translucent image using the best available way of representing translucency.
	translucentImage:at:sourceRect: Draw a translucent image using the best available way of representing translucency. Note: This will be fixed in the future.

	drawing-obsolete	top
	image:at: Note: This protocol is deprecated. Use #paintImage: instead.
	image:at:rule: Note: This protocol is deprecated. Use one of the explicit image drawing messages (#paintImage, #drawImage) instead.
	imageWithOpaqueWhite:at: Note: This protocol is deprecated. Use #drawImage: instead

	drawing-ovals	top
	fillOval:color:
	fillOval:color:borderWidth:borderColor: Fill the given oval.
	fillOval:fillStyle: Fill the given oval.
	fillOval:fillStyle:borderWidth:borderColor: Fill the given oval. Note: The default implementation does not recognize any enhanced fill styles
	frameOval:color:
	frameOval:width:color:

	drawing-polygons	top
	drawPolygon:color:borderWidth:borderColor: Draw the given polygon.
	drawPolygon:fillStyle: Fill the given polygon.
	drawPolygon:fillStyle:borderWidth:borderColor: Fill the given polygon. Note: The default implementation does not recognize any enhanced fill styles

	drawing-rectangles	top
	fillRectangle:color: Fill the rectangle using the given color
	fillRectangle:fillStyle: Fill the given rectangle. Note: The default implementation does not recognize any enhanced fill styles
	fillRectangle:fillStyle:borderStyle: Fill the given rectangle.
	frameAndFillRectangle:fillColor:borderWidth:borderColor: Draw the rectangle using the given attributes
	frameAndFillRectangle:fillColor:borderWidth:topLeftColor:bottomRightColor: Draw the rectangle using the given attributes. Note: This is a *very* simple implementation
	frameRectangle:color:
	frameRectangle:width:color:

	drawing-support	top
	cache:using:during: Cache the execution of aBlock by the given cache. Note: At some point we may want to actually *create* the cache here; for now we're only using it.
	clipBy:during: Set a clipping rectangle active only during the execution of aBlock. Note: In the future we may want to have more general clip shapes - not just rectangles
	preserveStateDuring: Preserve the full canvas state during the execution of aBlock
	transformBy:clippingTo:during: Transform the receiver by the given display transformation during the execution of aBlock. The given clip rectangle defines the *global* (e.g., outer) rectangle against which the receiver should clip (which would be equivalent to 'self clipRect: aClipRect; transformBy: aDisplayTransform').
	transformBy:clippingTo:during:smoothing: Transform the receiver by the given display transformation during the execution of aBlock. The given clip rectangle defines the *global* (e.g., outer) rectangle against which the receiver should clip (which would be equivalent to 'self clipRect: aClipRect; transformBy: aDisplayTransform').
	translateBy:during: Set a translation only during the execution of aBlock.
	translateTo:clippingTo:during: Set a new origin and clipping rectangle only during the execution of aBlock.

	initialization	top
	finish If there are any pending operations on the receiver complete them. Do not return before all modifications have taken effect.
	flush
	reset Reset the canvas.

	other	top
	flushDisplay Dummy .
	forceToScreen: dummy
	translateBy:clippingTo:during:

	private	top
	image:at:sourceRect:rule: Note: The public use of this protocol is deprecated. It will become private. Nobody in the outside world must assume that a thing like a combination rule has any specific effect.
	image:at:sourceRect:rule:alpha: Privately used for blending forms w/ constant alpha. Fall back to simpler case by defaul.

	testing	top
	doesRoundedCorners
	isBalloonCanvas
	isShadowDrawing
	isVisible: Return true if the given rectangle is (partially) visible
	seesNothingOutside: Return true if this canvas will not touch anything outside aRectangle

	configuring	top
	filterSelector