Sain (サイン)

A Compose Multiplatform library for capturing and exporting signatures as ImageBitmap with customizable options. Perfect for electronic signature, legal documents and more.

Including it in your project:

Add the Maven Central repository if it is not already there:

repositories {
    mavenCentral()
}

In multiplatform projects, add a dependency to the commonMain source set dependencies

kotlin {
    sourceSets {
        commonMain {
             dependencies {
                 implementation("io.github.joelkanyi:sain:2.0.3")
             }
        }
    }
}

In Android projects, add the dependency to your dependencies block in your app's build.gradle file:

dependencies {
    implementation("io.github.joelkanyi:sain:2.0.3")
}

For those using Gradle Version Catalog, you can add the dependency as follows:

[versions]
sain = "2.0.3"

[libraries]
sain = { module = "io.github.joelkanyi:sain", version.ref = "sain" }

Add then include the dependency in your project as follows:

dependencies {
    implementation(libs.sain)
}

Usage

Add the Sain composable into your project and customize it according to your needs:

var imageBitmap: ImageBitmap? by remember {
    mutableStateOf(null)
}

val state = remember {
    SignatureState()
}

Sain(
    state = state,
    modifier = Modifier
        .fillMaxWidth()
        .height(250.dp)
        .border(
            BorderStroke(
                width = .5.dp,
                color = MaterialTheme.colorScheme.onSurface
            ),
            shape = RoundedCornerShape(8.dp)
        ),
    onComplete = { signatureBitmap ->
        if (signatureBitmap != null) {
            imageBitmap = signatureBitmap
        } else {
            println("Signature is empty")
        }
    },
) { action ->
    Row(
        modifier = Modifier
            .padding(top = 16.dp)
            .fillMaxWidth(),
        horizontalArrangement = Arrangement.spacedBy(16.dp)
    ) {
        Button(
            modifier = Modifier.weight(1f),
            onClick = {
                imageBitmap = null
                action(SignatureAction.CLEAR)
            }) {
            Text("Clear")
        }
        Button(
            modifier = Modifier.weight(1f),
            onClick = {
                action(SignatureAction.COMPLETE)
            }) {
            Text("Complete")
        }
    }
}

Actions

The Sain composable takes in an actions parameter which is a lambda that takes in a SignatureAction enum. The SignatureAction enum has two values:

• CLEAR - Clears the signature
• COMPLETE - Completes the signature and returns the signature as an ImageBitmap in the onComplete lambda

Customization

• signatureColor - The color of the signature
• signatureThickness - The thickness of the signature
• modifier - The modifier for the Sain composable which allows you to customize the size, shape, background, border etc of the signature view

Known Issues

The library works well in one orientation. If you rotate the device, the signature will be lost. This is a known issue and will be fixed in the next release.

Note: The library is now hosted on Maven Central. If you were using the previous version hosted on Jitpack, please update your dependencies to the latest version.

Demo

Android

iOS

Desktop

Web Wasm

Web JS

License

Copyright 2023 Joel Kanyi

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.