Implement 'pan-with-cursor' for relative action mode

app/src/main/java/com/gaurav/avnc/ui/vnc/Dispatcher.kt

@@ -266,6 +266,7 @@ class Dispatcher(private val activity: VncActivity) {
                 y = y.coerceIn(0f, viewModel.frameState.fbHeight - 1)
             }
             doButtonDown(PointerButton.None, pointerPosition)
+            viewModel.showFbPoint(pointerPosition)
         }
 
         override fun doDrag(p: PointF, dx: Float, dy: Float) {

app/src/main/java/com/gaurav/avnc/ui/vnc/FrameState.kt

@@ -194,6 +194,24 @@ class FrameState(private val minZoomScale: Float = 0.5F, private val maxZoomScal
             return null
     }
 
+    /**
+     * Makes sure that framebuffer point [fbX],[fbY] is visible.
+     * If point is outside of visible area, frame is panned to make the it visible.
+     */
+    fun showFbPoint(fbX: Float, fbY: Float) {
+        val vpX = fbX * scale + frameX
+        val vpY = fbY * scale + frameY
+        var dx = 0f
+        var dy = 0f
+
+        if (vpX < 0) dx = -vpX
+        if (vpX >= vpWidth) dx = vpWidth - vpX - 1
+        if (vpY < 0) dy = -vpY
+        if (vpY >= vpHeight) dy = vpHeight - vpY - 1
+
+        pan(dx, dy)
+    }
+
     private fun calculateBaseScale() {
         if (fbHeight == 0F || fbWidth == 0F || windowHeight == 0F)
             return  //Not enough info yet

app/src/main/java/com/gaurav/avnc/viewmodel/VncViewModel.kt

@@ -9,6 +9,7 @@
 package com.gaurav.avnc.viewmodel
 
 import android.app.Application
+import android.graphics.PointF
 import android.util.Log
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.viewModelScope
@@ -277,6 +278,11 @@ class VncViewModel(app: Application) : BaseViewModel(app), VncClient.Observer {
         frameViewRef.get()?.requestRender()
     }
 
+    fun showFbPoint(fbPoint: PointF) {
+        frameState.showFbPoint(fbPoint.x, fbPoint.y)
+        frameViewRef.get()?.requestRender()
+    }
+
     /**************************************************************************
      * Clipboard Sync
      **************************************************************************/

app/src/test/java/com/gaurav/avnc/ui/FrameStateTest.kt

@@ -156,4 +156,27 @@ class FrameStateTest {
         assertEquals(-100f, state.frameX) //Right side of frame and Viewport are aligned
         assertEquals(-100f, state.frameY) //Bottom side of frame and Viewport are aligned
     }
+
+    @Test
+    fun showFbPointTest() {
+        val state = FrameState()
+        state.setViewportSize(50f, 50f)
+        state.setFramebufferSize(100f, 100f)
+        
+        state.showFbPoint(49f, 49f)
+        assertEquals(0f, state.frameX)
+        assertEquals(0f, state.frameY)
+
+        state.showFbPoint(50f, 50f)
+        assertEquals(-1f, state.frameX)
+        assertEquals(-1f, state.frameY)
+
+        state.showFbPoint(0f, 0f)
+        assertEquals(0f, state.frameX)
+        assertEquals(0f, state.frameY)
+
+        state.showFbPoint(99f, 99f)
+        assertEquals(-50f, state.frameX)
+        assertEquals(-50f, state.frameY)
+    }
 }