dac5ea57f4
* "create use paths" --> "create and use paths" * Use ES6 syntax in code example (`var` --> `const`/`let`)
84 lines
2.3 KiB
Markdown
84 lines
2.3 KiB
Markdown
---
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title: Paths
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---
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## Paths in Canvas
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Paths are the building block of drawing in Canvas. A path is just a shape. Then, the shape can be drawn on by either stroking it or filling it.
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We can create and use paths with `beginPath`, `fill`, and `stroke`.
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```js
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ctx.beginPath();
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ctx.rect(0, 0, 100, 100);
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ctx.fillStyle="black";
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ctx.fill();
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```
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This creates a black square in the upper-right corner of the canvas. We can change strokes and fills with `strokeStyle` and `fillStyle`, which both take CSS-like color strings. We can also use `lineWidth` to make strokes thicker.
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```js
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ctx.beginPath();
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ctx.moveTo(0,0);
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ctx.lineTo(300,150);
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ctx.moveTo(0, 100);
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ctx.lineTo(300, 250);
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ctx.strokeStyle="red";
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ctx.lineWidth=2;
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ctx.stroke();
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```
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There are four basic drawing functions: `rect`, `moveTo`, `lineTo`, and `arc`.
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- `rect(x, y, width, height)` adds a rectangle created from (`x`,`y`) of dimensions (`width`, `height`) to the path.
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- `moveTo(x,y)` moves the pen to a point on the canvas
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- `lineTo(x,y)` moves the pen to a point on the canvas, then adds a line between the new point and the old point to the path.
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- `arc(x, y, r, ti, tf)` adds an arc (a portion of a circle) at (`x`,`y`), of radius `r`, and from angle `ti` to `tf` to the path.
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Note that these functions add to the working path. They don't create new paths.
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```js
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//example 1
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ctx.beginPath();
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ctx.rect(0, 0, 50, 50);
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ctx.rect(100, 100, 50, 50);
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ctx.fill();
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//example 2
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ctx.beginPath();
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ctx.rect(0, 0, 50, 50);
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ctx.beginPath();
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ctx.rect(100, 100, 50, 50);
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ctx.fill();
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```
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The first example will draw two squares, while the second will only draw one since `beginPath` discarded the first rectangle on the old working path.
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This fact leads to a common mistake in making `canvas` animations.
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```js
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const y = 0;
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let x = 0;
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function draw() {
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ctx.clearRect(0, 0, canvas.width, canvas.height);
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ctx.rect(x, y, 50, 50);
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ctx.fill();
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x+=1;
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window.requestAnimationFrame(draw);
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}
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window.requestAnimationFrame(draw);
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```
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The above animation, which is supposed to make a square move across the screen, instead creates a long black bar. The reason is that `beginPath` is not called inside the `draw` loop.
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To read more about animation, see the [Animation](/articles/canvas/animation-in-canvas/) page.
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#### More Information:
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- [MDN Canvas API](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API)
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