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DrawScope：线条、矩形与圆形

在画布上绘制基本图形。

DrawScope：线条、矩形与圆形 是 CoddyKit 上的免费 Jetpack Compose Academy 课时。这是第 1 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Jetpack Compose Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Jetpack Compose Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Meet the Canvas

The Canvas Composable hands you a blank drawing surface. Inside it you paint pixels directly instead of stacking other Composables.

Canvas(modifier = Modifier.size(200.dp)) {
    // drawing goes here
}

Inside DrawScope

The lambda you pass to Canvas runs inside a DrawScope. That receiver gives you draw functions and the current size to work with.

Know Your Size

DrawScope exposes size, the area you can paint. Read size.width and size.height so your art scales to whatever space it gets.

Canvas(Modifier.fillMaxSize()) {
    val w = size.width
    val h = size.height
}

Draw a Line

Use drawLine to connect two points. You pass a color, a start Offset, an end Offset, and a stroke width.

drawLine(
    color = Color.Blue,
    start = Offset(0f, 0f),
    end = Offset(size.width, size.height),
    strokeWidth = 4f
)

Pixels Are Floats

Every coordinate here is a Float in pixels, not dp. The origin (0,0) sits at the top-left and x grows right, y grows down.

Offset Points the Way

An Offset is just an x and y pair. You will build almost every shape position from Offsets, so they show up everywhere on the canvas.

val center = Offset(size.width / 2, size.height / 2)

Draw a Rectangle

Call drawRect with a color, a topLeft Offset, and a Size. Leave topLeft out and it fills the whole canvas for you.

drawRect(
    color = Color.Green,
    topLeft = Offset(20f, 20f),
    size = Size(100f, 60f)
)

Draw a Circle

Use drawCircle with a color, a radius, and a center Offset. Center it on the canvas and you get a perfectly placed dot.

drawCircle(
    color = Color.Red,
    radius = 50f,
    center = center
)

Fill or Stroke

Each shape takes a style. The default is solid Fill, but pass Stroke to draw just the outline with a width you choose.

drawCircle(
    color = Color.Black,
    radius = 50f,
    style = Stroke(width = 6f)
)

Control Transparency

Pass an alpha between 0f and 1f to fade any shape. Stack a few translucent circles and you get a soft layered glow.

drawCircle(color = Color.Magenta, radius = 60f, alpha = 0.4f)

Order Is Layering

Draw calls paint in order, so later shapes sit on top of earlier ones. Think of it like dropping cutouts onto a page one by one.

Quick Check

Where does the canvas coordinate system begin?

Recap

You learned the Canvas basics: draw inside DrawScope, read size, and paint lines, rects, and circles with Offsets and float pixels. Order is everything! 🎨

常见问题解答

「DrawScope：线条、矩形与圆形」课时是免费的吗？

是的 — 「DrawScope：线条、矩形与圆形」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Jetpack Compose Academy 课程的其余内容，请升级到 CoddyKit PRO。 Jetpack Compose Academy 课程共包含 4 节课。

「DrawScope：线条、矩形与圆形」这节课中我会学到什么？

在画布上绘制基本图形。你通过在浏览器中直接运行的动手代码来练习 Jetpack Compose Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Jetpack Compose Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Jetpack Compose Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 1 节课，共 4 节。

「DrawScope：线条、矩形与圆形」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Jetpack Compose Academy 课中编写并运行代码吗？

能。每节 Jetpack Compose Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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