bristle
v0.2.9
Published
A small JS library for drawing dynamic paths into html canvas elements.
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Bristle
What is it?
A small JS library to help make drawing dynamic paths into <canvas>
elements easier.
Gist
A simple example
Note: For the path functions, 2D vectors are represented as two element arrays, so [x, y]
let canvasCtx = document.querySelector('#my-canvas').getContext('2d');
let bristleObj = bristle(canvasCtx);
canvasCtx.beginPath();
bristleObj.sequence((bristleCtx) => {
bristleCtx
.moveTo([10, 10])
.lineTo([50, 50)
.lineTo([50, 10])
.commit(); //This will send our stored instructions into the 2D context object.
});
canvasCtx.fillStyle = '#4A4';
canvasCtx.fill();
Ok, so that's the very basics. Now, let's add some transformations that are applied to subsequent input operations.
let canvasCtx = document.querySelector('#my-canvas').getContext('2d');
let bristleObj = bristle(canvasCtx);
bristleObj.sequence((bristleCtx) => {
// The bristle 'context' object has a transform stack we can push offsets to.
bristleCtx.pushTransform([0, 10])
.moveTo([0, -10])
.lineTo([-10, 0])
// Transforms combine as we push them to the stack,
// so our current global transform point is [0, 50].
.pushTransform([0, 40])
.lineTo([-10, 0])
.lineTo([0, 10])
.lineTo([10, 0])
// And now we're back to [0, 10].
.popTransform()
.lineTo([10, 0])
.commit((canvasCtx, trigger) => { //we can pass a function to .commit
// The predicate we pass to .commit gets the original CanvasRenderingContext2D
// object we passed in when we created bristleCtx.
canvasCtx.beginPath();
// By calling this trigger function, all our stored instructions
// get dumped into the canvas context
trigger();
// We can do our canvas context drawing
// configuration/execution in this predicate function
canvasCtx.fillStyle = '#0C0';
canvasCtx.fill();
});
});
And now, we can break our paths up into sequences that can be chained together
let canvasCtx = document.querySelector('#my-canvas').getContext('2d');
let bristleObj = bristle(canvasCtx);
bristleObj.sequence((bristleCtx) =>
bristleCtx.pushTransform([-40, 0])
.moveTo([-10, 0])
// The .sequence method takes a handler function
.sequence((seqCtx) => {
// The first argument passed into the
// sequence handler funtion is our bristleCtx object
// unless that behavior has been overridden
seqCtx.pushTransform([40, 40])
.lineTo([-20, 10])
.lineTo([20, 10]);
seqCtx.sequence((seqCtx) => {
seqCtx.pushTransform([40, -40])
.lineTo([10, 0])
.lineTo([-10, 0]);
});
// When we return from a sequence, our transform is
// right where we left it.
seqCtx.lineTo([0, -10]);
});
});