Canvas

Composable Function

Common

@Composable
fun Canvas(modifier: Modifier, onDraw: DrawScope.() -> Unit) = Spacer(modifier.drawBehind(onDraw))

Component that allow you to specify an area on the screen and perform canvas drawing on this area. You MUST specify size with modifier, whether with exact sizes via Modifier.size modifier, or relative to parent, via Modifier.fillMaxSize, ColumnScope.weight, etc. If parent wraps this child, only exact sizes must be specified.

Parameters


modifier	mandatory modifier to specify size strategy for this composable
onDraw	lambda that will be called to perform drawing. Note that this lambda will be called during draw stage, you have no access to composition scope, meaning that `Composable` function invocation inside it will result to runtime exception

Common

@Composable
fun Canvas(modifier: Modifier, contentDescription: String, onDraw: DrawScope.() -> Unit) =
    Spacer(modifier.drawBehind(onDraw).semantics { this.contentDescription = contentDescription })

Parameters


modifier	mandatory modifier to specify size strategy for this composable
contentDescription	text used by accessibility services to describe what this canvas represents. This should be provided unless the canvas is used for decorative purposes or as part of a larger entity already described in some other way. This text should be localized, such as by using `androidx.compose.ui.res.stringResource`
onDraw	lambda that will be called to perform drawing. Note that this lambda will be called during draw stage, you have no access to composition scope, meaning that `Composable` function invocation inside it will result to runtime exception

Code Examples

CanvasSample

@Composable
fun CanvasSample() {
    Canvas(modifier = Modifier.size(100.dp)) {
        drawRect(Color.Magenta)
        inset(10.0f) {
            drawLine(
                color = Color.Red,
                start = Offset.Zero,
                end = Offset(size.width, size.height),
                strokeWidth = 5.0f,
            )
        }
    }
}

CanvasPieChartSample

@Composable
fun CanvasPieChartSample() {
    Canvas(
        contentDescription = "Pie chart: 80% apples, 20% bananas (localized string)",
        modifier = Modifier.size(300.dp),
    ) {
        // Apples (80%)
        drawCircle(color = Color.Red, radius = size.width / 2)
        // Bananas (20%)
        drawArc(
            color = Color.Yellow,
            startAngle = 0f,
            sweepAngle = 360f * 0.20f,
            useCenter = true,
            topLeft = Offset(0f, (size.height - size.width) / 2f),
            size = Size(size.width, size.width),
        )
    }
}