commonMain.com.seanproctor.signaturepad.SignaturePadState.kt Maven / Gradle / Ivy

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A signature pad for Jetbrains Compose.
The newest version!
package com.seanproctor.signaturepad

import androidx.compose.runtime.Composable
import androidx.compose.runtime.mutableStateListOf
import androidx.compose.runtime.remember
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.graphics.Canvas
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.ImageBitmap
import androidx.compose.ui.graphics.Paint
import kotlin.math.min

public interface SignaturePadState {
    public fun gestureStarted(point: Offset)
    public fun gestureMoved(point: Offset)
    public fun drawSignature(canvas: Canvas, penColor: Color, penWidth: Float)
    public fun setSize(newWidth: Int, newHeight: Int)
    public fun clear()
    public fun drawOnBitmap(bitmap: ImageBitmap, penColor: Color, penWidth: Float)
}

public class SignaturePadStateImpl : SignaturePadState {

    private val points = mutableListOf()
    private val beziers = mutableStateListOf()
    private var width: Int = 0
    private var height: Int = 0

    override fun gestureStarted(point: Offset) {
        // Reset state
        points.clear()
        // First segment isn't drawn
        addPoint(point)
        addPoint(point)
    }

    override fun gestureMoved(point: Offset) {
        addPoint(point)
    }

    private fun addPoint(point: Offset) {
        points.add(point)

        // Need 4 points to draw a cubic bezier curve.
        if (points.size > 3) {
            // We're connecting the middle 2 points
            val prevPoint = points[0]
            val startPoint = points[1]
            val endPoint = points[2]
            val nextPoint = points[3]

            // The Bezier's width starts out as the last curve's final width, and
            // gradually changes to the stroke width just calculated. The new
            // width calculation is based on the velocity between the Bezier's
            // start and end points.
            val bezier = Bezier(startPoint, endPoint, prevPoint, nextPoint)
            beziers.add(bezier)

            // Remove the first point
            points.removeAt(0)
        }
    }

    override fun drawSignature(canvas: Canvas, penColor: Color, penWidth: Float) {
        val paint = Paint()
        paint.color = penColor
        paint.strokeWidth = penWidth
        beziers.forEach {
            it.draw(canvas, paint)
        }
    }

    override fun setSize(newWidth: Int, newHeight: Int) {
        width = newWidth
        height = newHeight
        clear()
    }

    override fun clear() {
        points.clear()
        beziers.clear()
    }

    override fun drawOnBitmap(
        bitmap: ImageBitmap,
        penColor: Color,
        penWidth: Float,
    ) {
        val scaling = min(bitmap.width / width.toFloat(), bitmap.height / height.toFloat())
        val canvas = Canvas(bitmap)
        val paint = Paint()
        paint.color = penColor
        paint.strokeWidth = penWidth
        beziers.forEach {
            it.scale(scaling).draw(canvas, paint)
        }
    }
}

@Composable
public fun rememberSignaturePadState(): SignaturePadState {
    return remember { SignaturePadStateImpl() }
}