- From: David Levin <levin@google.com>
- Date: Mon, 22 Feb 2010 11:13:35 -0800
I've talked with some other folks on WebKit (Maciej and Oliver) about having
a canvas that is available to workers. They suggested some nice
modifications to make it an offscreen canvas, which may be used in the
Document or in a Worker.
Proposal:
Introduce an OffscreenCanvas which may be created from a Document or a
Worker context.
interface OffscreenCanvas {
attribute unsigned long width;
attribute unsigned long height;
DOMString toDataURL (in optional DOMString type, in any... args);
object getContext(in DOMString contextId);
};
When it is created in the Worker context, OffscreenCanvas.getContext("2d")
returns a CanvasWorkerContext2D. In the Document context, it returns a
CanvasRenderingContext2D.
The base class for both CanvasWorkerContext2D and CanvasRenderingContext2D
is CanvasContext2D. CanvasContext2D is just like a CanvasRenderingContext2D
except for omitting the font methods and any method which uses HTML
elements. It does have some replacement methods for createPattern/drawImage
which take an OffscreenCanvas. The canvas object attribute is either a
HTMLCanvasElement or an OffscreenCanvas depending on what the canvas context
came from.
interface CanvasContext2D {
readonly attribute object canvas;
void save();
void restore();
void scale(in float sx, in float sy);
void rotate(in float angle);
void translate(in float tx, in float ty);
void transform(in float m11, in float m12, in float m21, in float
m22, in float dx, in float dy);
void setTransform(in float m11, in float m12, in float m21, in float
m22, in float dx, in float dy);
attribute float globalAlpha;
attribute [ConvertNullToNullString] DOMString
globalCompositeOperation;
CanvasGradient createLinearGradient(in float x0, in float y0, in
float x1, in float y1)
raises (DOMException);
CanvasGradient createRadialGradient(in float x0, in float y0, in
float r0, in float x1, in float y1, in float r1)
raises (DOMException);
CanvasPattern createPattern(in OffscreenCanvas image, in DOMString
repetition);
attribute float lineWidth;
attribute [ConvertNullToNullString] DOMString lineCap;
attribute [ConvertNullToNullString] DOMString lineJoin;
attribute float miterLimit;
attribute float shadowOffsetX;
attribute float shadowOffsetY;
attribute float shadowBlur;
attribute [ConvertNullToNullString] DOMString shadowColor;
void clearRect(in float x, in float y, in float width, in float
height);
void fillRect(in float x, in float y, in float width, in float
height);
void strokeRect(in float x, in float y, in float w, in float h);
void beginPath();
void closePath();
void moveTo(in float x, in float y);
void lineTo(in float x, in float y);
void quadraticCurveTo(in float cpx, in float cpy, in float x, in
float y);
void bezierCurveTo(in float cp1x, in float cp1y, in float cp2x, in
float cp2y, in float x, in float y);
void arcTo(in float x1, in float y1, in float x2, in float y2, in
float radius);
void rect(in float x, in float y, in float width, in float height);
void arc(in float x, in float y, in float radius, in float
startAngle, in float endAngle, in boolean anticlockwise);
void fill();
void stroke();
void clip();
boolean isPointInPath(in float x, in float y);
void drawImage(in OffscreenCanvas image, in float dx, in float dy,
in optional float dw, in optional float dh);
void drawImage(in OffscreenCanvas image, in float sx, in float sy,
in float sw, in float sh, in float dx, in float dy, in float dw, in float
dh);
// pixel manipulation
ImageData createImageData(in float sw, in float sh)
raises (DOMException);
ImageData getImageData(in float sx, in float sy, in float sw, in
float sh)
raises(DOMException);
void putImageData(in ImageData imagedata, in float dx, in float dy,
in optional float dirtyX, in optional float dirtyY, in optional float
dirtyWidth, in optional float dirtyHeight]);
};
interface CanvasWorkerContext2D : CanvasContext2D {
};
interface CanvasRenderingContext2D : CanvasContext2D {
CanvasPattern createPattern(in HTMLImageElement image, in DOMString
repetition);
CanvasPattern createPattern(in HTMLCanvasElement image, in
DOMString repetition);
CanvasPattern createPattern(in HTMLVideoElement image, in DOMString
repetition);
// focus management
boolean drawFocusRing(in Element element, in float xCaret, in float
yCaret, in optional boolean canDrawCustom);
// text
attribute DOMString font;
attribute DOMString textAlign;
attribute DOMString textBaseline;
void fillText(in DOMString text, in float x, in float y, in optional
float maxWidth);
void strokeText(in DOMString text, in float x, in float y, in
optional float maxWidth);
TextMetrics measureText(in DOMString text);
// drawing images
void drawImage(in HTMLImageElement image, in float dx, in float dy,
in optional float dw, in float dh);
void drawImage(in HTMLImageElement image, in float sx, in float sy,
in float sw, in float sh, in float dx, in float dy, in float dw, in float
dh);
void drawImage(in HTMLVideoElement image, in float dx, in float dy,
in optional float dw, in optional float dh);
void drawImage(in HTMLVideoElement image, in float sx, in float sy,
in float sw, in float sh, in float dx, in float dy, in float dw, in float
dh);
void drawImage(in HTMLCanvasElement image, in float dx, in float dy,
in optional float dw, in float dh);
void drawImage(in HTMLCanvasElement image, in float sx, in float sy,
in float sw, in float sh, in float dx, in float dy, in float dw, in float
dh);
};
Questions and comments are welcome.
Note that something similar did come up in December and this proposal avoids
doing any text related items in the offscreen canvas which was a concern
brought up by Robert O'Callahan at the time (
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-December/024478.html
).
Dave
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Received on Monday, 22 February 2010 11:13:35 UTC