Snap zoom to 100%

Re: #170
gujjwal00 · Mar 1, 2024 · c92c8c4 · c92c8c4
1 parent 1a1779e
commit c92c8c4
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Showing 3 changed files with 114 additions and 2 deletions.
diff --git a/app/src/androidTest/java/com/gaurav/avnc/ui/vnc/FrameStateTest.kt b/app/src/androidTest/java/com/gaurav/avnc/ui/vnc/FrameStateTest.kt
@@ -208,4 +208,58 @@ class FrameStateTest {
         assertEquals(-2f, snapshot.frameX)
         assertEquals(-3f, snapshot.frameY)
     }
+
+
+    /*********************** Snapping ****************************************/
+    @Test
+    fun noSnappingInInitialState() {
+        val state = FrameState()
+
+        state.updateZoom(1.02f)
+        assertEquals(1.02f, state.zoomScale)
+
+        state.setZoom(1f, 1f)
+        state.updateZoom(.98f)
+        assertEquals(.98f, state.zoomScale)
+    }
+
+    @Test
+    fun snapUpWhenGoingBelow100Percent() {
+        val state = FrameState()
+
+        state.setZoom(2f, 2f)
+        assertEquals(2f, state.zoomScale)
+
+        state.updateZoom(1.5f / 2f)
+        assertEquals(1.5f, state.zoomScale)
+
+        state.updateZoom(1f / 1.5f)
+        assertEquals(1f, state.zoomScale)
+
+        state.updateZoom(.9f / 1f)
+        assertEquals(1f, state.zoomScale) // 90% should be snapped-up to 100%
+
+        state.updateZoom(.5f)  // Decreased too much,
+        assertTrue(state.zoomScale < 1)  // should no longer be snapped
+    }
+
+    @Test
+    fun snapDownWhenGoingAbove100Percent() {
+        val state = FrameState()
+
+        state.setZoom(.5f, .5f)
+        assertEquals(.5f, state.zoomScale)
+
+        state.updateZoom(.8f / .5f)
+        assertEquals(.8f, state.zoomScale)
+
+        state.updateZoom(1f / .8f)
+        assertEquals(1f, state.zoomScale)
+
+        state.updateZoom(1.1f / 1f)
+        assertEquals(1f, state.zoomScale) // 110% should be snapped-down to 100%
+
+        state.updateZoom(2f)   // Increased too much,
+        assertTrue(state.zoomScale > 1)  // should no longer be snapped
+    }
 }
diff --git a/app/src/main/java/com/gaurav/avnc/ui/vnc/Dispatcher.kt b/app/src/main/java/com/gaurav/avnc/ui/vnc/Dispatcher.kt
@@ -127,7 +127,10 @@ class Dispatcher(private val activity: VncActivity) {
      **************************************************************************/
 
     fun onGestureStart() = config.defaultMode.onGestureStart()
-    fun onGestureStop(p: PointF) = config.defaultMode.onGestureStop(p)
+    fun onGestureStop(p: PointF) {
+        config.defaultMode.onGestureStop(p)
+        viewModel.frameState.onGestureStop()
+    }
 
     fun onTap1(p: PointF) = config.tap1Action(p)
     fun onTap2(p: PointF) = config.tap2Action(p)

diff --git a/app/src/main/java/com/gaurav/avnc/ui/vnc/FrameState.kt b/app/src/main/java/com/gaurav/avnc/ui/vnc/FrameState.kt
@@ -11,6 +11,7 @@ package com.gaurav.avnc.ui.vnc
 import android.graphics.PointF
 import android.graphics.RectF
 import com.gaurav.avnc.ui.vnc.FrameState.Snapshot
+import kotlin.math.abs
 import kotlin.math.max
 import kotlin.math.min
 
@@ -188,8 +189,9 @@ class FrameState(
      */
     fun updateZoom(scaleFactor: Float): Float = withLock {
         val oldScale = zoomScale
+        val newScale = zoomScale * scaleFactor
 
-        zoomScale *= scaleFactor
+        zoomScale = snapZoom(oldScale, newScale)
         coerceValues()
 
         return zoomScale / oldScale //Applied scale factor
@@ -254,6 +256,13 @@ class FrameState(
                         vpWidth = vpWidth, vpHeight = vpHeight, scale = scale)
     }
 
+    /**
+     * Signaled when gesture ends
+     */
+    fun onGestureStop() {
+        resetSnapState()
+    }
+
     private fun calculateBaseScale() {
         if (fbHeight == 0F || fbWidth == 0F || windowHeight == 0F)
             return  //Not enough info yet
@@ -288,4 +297,50 @@ class FrameState(
         return if (diff >= 0) diff / 2 + safeMin       //Frame will be smaller than safe area, so center it
         else current.coerceIn(diff + safeMin, safeMin) //otherwise, make sure safe area is completely filled.
     }
+
+
+    /**
+     * Zoom scale snapping: It temporarily stops the scale at 100% when user is zooming.
+     * This way user don't have to reset zoom via "Reset zoom" button in toolbar.
+     */
+    private enum class Snap { None, Up, Down }
+
+    private var snapMode = Snap.None
+    private val snapLimit = 0.3f  // ±30% zoom
+    private var snapDelta = 0f
+
+    private fun snapZoom(oldZoom: Float, newZoom: Float): Float {
+        val deltaToOne = abs(newZoom - 1)
+        var result = newZoom
+
+        if (snapMode == Snap.Up) {
+            if (newZoom < 1) {                // Until snap limit is reached, snap up zoom to 1.0
+                snapDelta += deltaToOne
+                if (snapDelta < snapLimit)
+                    result = 1f
+            } else                            // Not crossed below 1.0 yet
+                snapDelta = 0f
+        }
+
+        if (snapMode == Snap.Down) {
+            if (newZoom > 1) {                // Until snap limit is reached, snap down zoom to 1.0
+                snapDelta += deltaToOne
+                if (snapDelta < snapLimit)
+                    result = 1f
+            } else                            // Not crossed above 1.0 yet
+                snapDelta = 0f
+        }
+
+        if (oldZoom > 1 && newZoom < oldZoom) // Greater than 1 but decreasing, so snap when going below 1
+            snapMode = Snap.Up
+        if (oldZoom < 1 && newZoom > oldZoom) // Lower than 1 but increasing, so snap when going above 1
+            snapMode = Snap.Down
+
+        return result
+    }
+
+    private fun resetSnapState() {
+        snapMode = Snap.None
+        snapDelta = 0f
+    }
 }