#include <canvas.h>

Collaboration diagram for CanvasRenderingContext2D:

Public Attributes
struct {
HTMLCanvasElement * canvas

char contextType [19]

char * font

char * textAlign

char * fillStyle

char * strokeStyle

char * lineCap

char * lineJoin

char * globalCompositeOperation

}	private

void(*	clearRect )(CanvasRenderingContext2D *this, double x, double y, double width, double height)

void(*	fillRect )(CanvasRenderingContext2D *this, double x, double y, double width, double height)

void(*	strokeRect )(CanvasRenderingContext2D *this, double x, double y, double width, double height)

void(*	fillText )(CanvasRenderingContext2D this, char text, double x, double y, double maxWidth)

void(*	strokeText )(CanvasRenderingContext2D this, char text, double x, double y, double maxWidth)

void(*	setLineWidth )(CanvasRenderingContext2D *this, double value)

double(*	getLineWidth )(CanvasRenderingContext2D *this)

void(*	setLineCap )(CanvasRenderingContext2D this, char type)

char (	getLineCap )(CanvasRenderingContext2D *this)

void(*	setLineJoin )(CanvasRenderingContext2D this, char type)

char (	getLineJoin )(CanvasRenderingContext2D *this)

char (	getFont )(CanvasRenderingContext2D *this)

void(*	setFont )(CanvasRenderingContext2D this, char value)

void(*	setTextAlign )(CanvasRenderingContext2D this, char value)

char (	getTextAlign )(CanvasRenderingContext2D *this)

void(*	setFillStyle )(CanvasRenderingContext2D this, char value)

char (	getFillStyle )(CanvasRenderingContext2D *this)

void(*	setStrokeStyle )(CanvasRenderingContext2D this, char value)

char (	getStrokeStyle )(CanvasRenderingContext2D *this)

void(*	beginPath )(CanvasRenderingContext2D *this)

void(*	closePath )(CanvasRenderingContext2D *this)

void(*	moveTo )(CanvasRenderingContext2D *this, double x, double y)

void(*	lineTo )(CanvasRenderingContext2D *this, double x, double y)

void(*	bezierCurveTo )(CanvasRenderingContext2D *this, double cp1x, double cp1y, double cp2x, double cp2y, double x, double y)

void(*	quadraticCurveTo )(CanvasRenderingContext2D *this, double cpx, double cpy, double x, double y)

void(*	arc )(CanvasRenderingContext2D *this, double x, double y, double radius, double startAngle, double endAngle)

void(*	arcTo )(CanvasRenderingContext2D *this, double x1, double y1, double x2, double y2, double radius)

void(*	ellipse )(CanvasRenderingContext2D *this, double x, double y, double radiusX, double radiusY, double rotation, double startAngle, double endAngle)

void(*	rect )(CanvasRenderingContext2D *this, double x, double y, double width, double height)

void(*	fill )(CanvasRenderingContext2D *this)

void(*	stroke )(CanvasRenderingContext2D *this)

void(*	clip )(CanvasRenderingContext2D *this)

int(*	isPointInPath )(CanvasRenderingContext2D *this, double x, double y)

int(*	isPointInStroke )(CanvasRenderingContext2D *this, double x, double y)

void(*	rotate )(CanvasRenderingContext2D *this, double angle)

void(*	scale )(CanvasRenderingContext2D *this, double x, double y)

void(*	translate )(CanvasRenderingContext2D *this, double x, double y)

void(*	transform )(CanvasRenderingContext2D *this, double a, double b, double c, double d, double e, double f)

void(*	setTransform )(CanvasRenderingContext2D *this, double a, double b, double c, double d, double e, double f)

void(*	resetTransform )(CanvasRenderingContext2D *this)

void(*	setGlobalAlpha )(CanvasRenderingContext2D *this, double value)

double(*	getGlobalAlpha )(CanvasRenderingContext2D *this)

void(*	setGlobalCompositeOperation )(CanvasRenderingContext2D this, char value)

char (	getGlobalCompositeOperation )(CanvasRenderingContext2D *this)

void(*	save )(CanvasRenderingContext2D *this)

void(*	restore )(CanvasRenderingContext2D *this)

HTMLCanvasElement (	getCanvas )(CanvasRenderingContext2D *this)

Detailed Description

Struct containing state and OO-like behavior of a CanvasRenderingContext2D structured similarly to how it would be exposed in JavaScript. This struct should not be instantiated, but rather obtained from an HTMLCanvas struct by calling its getContext() function pointer.

Function pointers in this struct can be called in an almost identical manner to their JavaScript equivalents, with a few idiomatic-C quirks. Firstly, every function takes as its first parameter a pointer to the struct itself. It's hard to access the struct's state within the function otherwise since we are just simulating OO. Secondly, some function parameters differ slightly from the JS implementations because we don't have overloading in C. For example, the fillText() function always expects the optional 'maxWidth' property. That parameter will be ignored if you provide a negative value, and there are comments written below with that and similar information.

You might notice that a lot of functions expect double parameters. That's because most of the equivalent JavaScript functions will accept doubles. Don't worry, providing int parameters will work just fine. (int) -> (double) is an implicit conversion in C; no cast required.

To summarize, a typical use of this struct might look like the following:

HTMLCanvas *canvas = createCanvas("myCanvas");
CanvasRenderingContext2D *ctx = canvas->getContext(canvas, "2d"); // only 2d is supported currently
ctx->setFillStyle(ctx, "#FF0000");
printf("I set the fill style to %s\n", ctx->getFillStyle(ctx));
ctx->fillRect(ctx, 50, 75, 100, 200);
freeCanvas(canvas);

Some state is pseudo-encapsulated in the 'private' member struct, such as pointers to dynamically allocated strings that will need to be freed when the HTMLCanvas is freed. Typically these are from JavaScript calls, allocated to return them to the user. Alternatively, functions with canonical string return types could be pigeon-holed into returning enum types, or we could make the user responsible for buffer allocation and expect an additional by-reference parameter to copy the string into. The in-JavaScript allocated string would need to be freed after returning its contents to the user, and the user would not know how large the buffer should be. So, when a string is exposed to the user, this struct keeps track of the pointers in order to free them when the HTMLCanvas parent struct is freed.

Member Data Documentation

◆ fillText

void(* CanvasRenderingContext2D::fillText) (CanvasRenderingContext2D *this, char *text, double x, double y, double maxWidth)

Parameters

maxWidth optional parameter. provide a value < 0.0 to ignore this parameter.

◆ private

struct { ... } CanvasRenderingContext2D::private

This anonymous struct encapsulates fields of the CanvasRenderingContext2D struct intended to be private. These are primarily pointers to memory allocated from JavaScript calls so that they can be freed when the canvas is no longer in use.

◆ strokeText

void(* CanvasRenderingContext2D::strokeText) (CanvasRenderingContext2D *this, char *text, double x, double y, double maxWidth)