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Improve full-screen image viewer gestures

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ajp_anton
2026-07-27 21:05:20 +00:00
parent 9f880c5f1c
commit 2efd923f7f
2 changed files with 76 additions and 10 deletions
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app/src/main/java/se/ajpanton/notificationlog/ZoomImageView.kt
+66 -9
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@@ -8,7 +8,10 @@ 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(
@@ -24,11 +27,29 @@ class ZoomImageView @JvmOverloads constructor(
private var lastX = 0f
private var lastY = 0f
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 val scaleDetector = ScaleGestureDetector(context, object : ScaleGestureDetector.SimpleOnScaleGestureListener() {
override fun onScaleBegin(detector: ScaleGestureDetector): Boolean {
lastFocusX = detector.focusX
lastFocusY = detector.focusY
return true
}
override fun onScale(detector: ScaleGestureDetector): Boolean {
val scale = (currentScale * detector.scaleFactor).coerceIn(minimumScale, minimumScale * MAX_ZOOM)
transform.postScale(scale / currentScale, scale / currentScale, detector.focusX, detector.focusY)
currentScale = scale
// A ScaleGestureDetector reports focus movement even when the two
// fingers stay the same distance apart, which is two-finger panning.
setScaleAround((currentScale * detector.scaleFactor).coerceIn(minimumScale, minimumScale * MAX_ZOOM), detector.focusX, detector.focusY)
transform.postTranslate(detector.focusX - lastFocusX, detector.focusY - lastFocusY)
lastFocusX = detector.focusX
lastFocusY = detector.focusY
constrain()
return true
}
@@ -39,11 +60,36 @@ class ZoomImageView @JvmOverloads constructor(
return true
}
override fun onDoubleTap(event: MotionEvent): Boolean {
val target = if (currentScale > minimumScale * 1.1f) minimumScale else minimumScale * DOUBLE_TAP_ZOOM
transform.postScale(target / currentScale, target / currentScale, event.x, event.y)
currentScale = target
constrain()
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
}
})
@@ -71,7 +117,7 @@ class ZoomImageView @JvmOverloads constructor(
lastY = event.y
dragging = false
}
MotionEvent.ACTION_MOVE -> if (!scaleDetector.isInProgress) {
MotionEvent.ACTION_MOVE -> if (event.pointerCount == 1 && !scaleDetector.isInProgress && !doubleTapZooming) {
val dx = event.x - lastX
val dy = event.y - lastY
if (dx != 0f || dy != 0f) {
@@ -82,6 +128,11 @@ class ZoomImageView @JvmOverloads constructor(
lastX = event.x
lastY = event.y
}
MotionEvent.ACTION_POINTER_UP -> {
val remainingPointer = if (event.actionIndex == 0) 1 else 0
lastX = event.getX(remainingPointer)
lastY = event.getY(remainingPointer)
}
MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
if (dragging) performClick()
}
@@ -91,6 +142,11 @@ class ZoomImageView @JvmOverloads constructor(
override fun performClick(): Boolean = super.performClick()
private fun setScaleAround(scale: Float, pivotX: Float, pivotY: Float) {
transform.postScale(scale / currentScale, scale / currentScale, pivotX, pivotY)
currentScale = scale
}
private fun resetToFit() {
val drawable = drawable ?: return
if (width == 0 || height == 0 || drawable.intrinsicWidth <= 0 || drawable.intrinsicHeight <= 0) return
@@ -128,5 +184,6 @@ 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
}
}