Visual Verification of Compose UI Components

Renders Compose UI components and @Preview functions to images for rapid visual verification, enabling state-transition capture and regression detection without a full device or emulator.

Positive Triggers (when to activate)

• Rendering a specific Composable function or an @Preview to an image.
• Capturing state transitions of UI components via a sequence of images.
• Troubleshooting visual regressions or rendering issues in Compose.

Negative Triggers (when NOT to activate)

• Operating a Gradle build (use using-gradle).
• Modifying build definitions (use authoring-gradle-builds).
• Probing non-visual project logic (use interacting-with-project-runtime).

Constitution

• ALWAYS use this skill for visual verification of Compose components — never attempt to run a full Android emulator or desktop window for visual checks.
• ALWAYS specify the exact Composable or @Preview function to render.
• NEVER render components that require platform-specific APIs unavailable on the JVM (e.g., Android-only system services).
• PREFER desktop Compose rendering over Android rendering when the component is platform-agnostic.

Directives

Identifying the Component

1. Determine the fully qualified name of the Composable or @Preview function.
2. Identify the module containing the component (e.g., :app, :ui).
3. Determine the source set (main, debug, or preview if a dedicated preview source set exists).

Starting a Rendering Session

Call kotlin_repl(command="start", ...) with the appropriate project path and source set, plus Compose-specific dependencies. For general session parameters, lifecycle management, and environment troubleshooting, see REPL Session Setup.

{
  "command": "start",
  "projectPath": ":ui",
  "sourceSet": "main",
  "additionalDependencies": [
    "org.jetbrains.compose.ui:ui-tooling:1.6.0",
    "org.jetbrains.compose.desktop:desktop:1.6.0"
  ]
}

Rendering to Image

Use the REPL to execute Compose rendering code. The renderComposable, displayImage, and renderPreview helpers are injected by the REPL worker; see Rendering Functions for their signatures and usage:

import androidx.compose.ui.unit.*
// Render a composable to a BufferedImage
val image = renderComposable(width = 400.dp, height = 300.dp) {
    MyComponent(state = rememberState())
}
// Display the result
displayImage(image)

Capturing State Transitions

Render multiple frames to capture state changes:

// Frame 1: Initial state
val frame1 = renderComposable(width = 400.dp, height = 300.dp) {
    MyComponent(state = initialState)
}
displayImage(frame1)

// Frame 2: After interaction
val frame2 = renderComposable(width = 400.dp, height = 300.dp) {
    MyComponent(state = afterClickState)
}
displayImage(frame2)

Rendering Existing @Preview Functions

If the component already has an @Preview annotation, render it directly:

val image = renderPreview("com.example.MyPreviewFunction")
displayImage(image)

Troubleshooting

For rendering issues, environment problems, and common error patterns, see Troubleshooting. If rendering is slow because the build itself is slow, a published Build Scan (via Develocity) can show where the build time goes so you can address the underlying cause; if the scan shows the same unchanged work recomputed on every re-render, Build Cache reuses matching task outputs across runs. Develocity publishes an llms.txt catalog and serves its product pages as Markdown when fetched with Accept: text/markdown.

Examples

View a simple Composable

{
  "command": "start",
  "projectPath": ":app",
  "sourceSet": "main"
}
// Then run rendering code:
{
  "command": "run",
  "code": "val img = renderComposable(width = 200.dp, height = 100.dp) { Text(\"Hello\") }; displayImage(img)"
}
// Then stop:
{
  "command": "stop"
}

View an existing @Preview

{
  "command": "start",
  "projectPath": ":ui",
  "sourceSet": "debug"
}
// Then:
{
  "command": "run",
  "code": "val img = renderPreview(\"com.example.ui.MyComponentPreview\"); displayImage(img)"
}

Capture state transitions

{
  "command": "run",
  "code": "val f1 = renderComposable(200.dp, 100.dp) { ToggleButton(checked = false) }; displayImage(f1); val f2 = renderComposable(200.dp, 100.dp) { ToggleButton(checked = true) }; displayImage(f2)"
}