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Use Android quick scale for image zoom

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ajp_anton
2026-07-27 21:21:26 +00:00
parent 0f3b4397f3
commit 1145713584
1 changed files with 10 additions and 51 deletions
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app/src/main/java/se/ajpanton/notificationlog/ZoomImageView.kt
+10 -51
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@@ -8,10 +8,7 @@ import android.util.AttributeSet
import android.view.GestureDetector
import android.view.MotionEvent
import android.view.ScaleGestureDetector
import android.view.ViewConfiguration
import androidx.appcompat.widget.AppCompatImageView
import kotlin.math.abs
import kotlin.math.exp
/** A fit-to-screen image which supports pinch zoom and one-finger panning. */
class ZoomImageView @JvmOverloads constructor(
@@ -29,13 +26,7 @@ class ZoomImageView @JvmOverloads constructor(
private var dragging = false
private var lastFocusX = 0f
private var lastFocusY = 0f
private var doubleTapZooming = false
private var doubleTapMoved = false
private var doubleTapX = 0f
private var doubleTapY = 0f
private var doubleTapStartY = 0f
private var doubleTapBaseScale = 1f
private val touchSlop = ViewConfiguration.get(context).scaledTouchSlop
private var pointerCount = 0
private val scaleDetector = ScaleGestureDetector(context, object : ScaleGestureDetector.SimpleOnScaleGestureListener() {
override fun onScaleBegin(detector: ScaleGestureDetector): Boolean {
lastFocusX = detector.focusX
@@ -44,10 +35,13 @@ class ZoomImageView @JvmOverloads constructor(
}
override fun onScale(detector: ScaleGestureDetector): Boolean {
// A ScaleGestureDetector reports focus movement even when the two
// fingers stay the same distance apart, which is two-finger panning.
// Focus movement while two fingers are down is two-finger panning.
// Quick scale has one pointer, so it remains pure zoom around its
// built-in double-tap anchor.
setScaleAround((currentScale * detector.scaleFactor).coerceIn(minimumScale, minimumScale * MAX_ZOOM), detector.focusX, detector.focusY)
transform.postTranslate(detector.focusX - lastFocusX, detector.focusY - lastFocusY)
if (pointerCount >= 2) {
transform.postTranslate(detector.focusX - lastFocusX, detector.focusY - lastFocusY)
}
lastFocusX = detector.focusX
lastFocusY = detector.focusY
constrain()
@@ -60,45 +54,11 @@ class ZoomImageView @JvmOverloads constructor(
return true
}
override fun onDoubleTap(event: MotionEvent): Boolean = true
override fun onDoubleTapEvent(event: MotionEvent): Boolean {
when (event.actionMasked) {
MotionEvent.ACTION_DOWN -> {
doubleTapZooming = true
doubleTapMoved = false
doubleTapX = event.x
doubleTapY = event.y
doubleTapStartY = event.y
doubleTapBaseScale = currentScale
}
MotionEvent.ACTION_MOVE -> if (doubleTapZooming) {
val distance = doubleTapStartY - event.y
if (abs(distance) > touchSlop) doubleTapMoved = true
val target = (doubleTapBaseScale * exp((distance / DOUBLE_TAP_DRAG_DISTANCE).toDouble()).toFloat())
.coerceIn(minimumScale, minimumScale * MAX_ZOOM)
setScaleAround(target, doubleTapX, doubleTapY)
constrain()
}
MotionEvent.ACTION_UP -> if (doubleTapZooming) {
if (!doubleTapMoved) {
val target = if (currentScale > minimumScale * 1.1f) minimumScale else minimumScale * DOUBLE_TAP_ZOOM
setScaleAround(target, doubleTapX, doubleTapY)
constrain()
}
doubleTapZooming = false
}
MotionEvent.ACTION_CANCEL -> doubleTapZooming = false
}
return true
}
})
init {
scaleType = ScaleType.MATRIX
// We implement double-tap-and-drag ourselves below. Leaving Android's
// quick-scale enabled makes both handlers modify the same matrix.
scaleDetector.isQuickScaleEnabled = false
scaleDetector.isQuickScaleEnabled = true
}
override fun setImageBitmap(bitmap: Bitmap?) {
@@ -112,6 +72,7 @@ class ZoomImageView @JvmOverloads constructor(
}
override fun onTouchEvent(event: MotionEvent): Boolean {
pointerCount = event.pointerCount
scaleDetector.onTouchEvent(event)
gestureDetector.onTouchEvent(event)
when (event.actionMasked) {
@@ -120,7 +81,7 @@ class ZoomImageView @JvmOverloads constructor(
lastY = event.y
dragging = false
}
MotionEvent.ACTION_MOVE -> if (event.pointerCount == 1 && !scaleDetector.isInProgress && !doubleTapZooming) {
MotionEvent.ACTION_MOVE -> if (event.pointerCount == 1 && !scaleDetector.isInProgress) {
val dx = event.x - lastX
val dy = event.y - lastY
if (dx != 0f || dy != 0f) {
@@ -186,7 +147,5 @@ class ZoomImageView @JvmOverloads constructor(
private companion object {
const val MAX_ZOOM = 6f
const val DOUBLE_TAP_ZOOM = 2.5f
const val DOUBLE_TAP_DRAG_DISTANCE = 280f
}
}