LowLatencyCanvasView

Artifact: androidx.graphics:graphics-core

Added in 1.0.3

Kotlin |Java

@RequiresApi(value = 29)
public final class LowLatencyCanvasView extends ViewGroup

java.lang.Object
↳	android.view.View
	↳	android.view.ViewGroup
		↳	androidx.graphics.lowlatency.LowLatencyCanvasView

View implementation that leverages a "front buffered" rendering system. This allows for lower latency graphics by leveraging a combination of front buffered alongside multi-buffered content layers. This class provides similar functionality to CanvasFrontBufferedRenderer, however, leverages the traditional View system for implementing the multi buffered content instead of a separate SurfaceControlCompat instance and entirely abstracts all SurfaceView usage for simplicity.

Drawing of this View's content is handled by a consumer specified LowLatencyCanvasView.Callback implementation instead of View.onDraw. Rendering here is done with a Canvas into a single buffer that is presented on screen above the rest of the View hierarchy content. This overlay is transient and will only be visible after LowLatencyCanvasView.renderFrontBufferedLayer is called and hidden after LowLatencyCanvasView.commit is invoked. After LowLatencyCanvasView.commit is invoked, this same buffer is wrapped into a bitmap and drawn within this View's View.onDraw implementation.

Calls to LowLatencyCanvasView.renderFrontBufferedLayer will trigger LowLatencyCanvasView.Callback.onDrawFrontBufferedLayer to be invoked to handle drawing of content with the provided Canvas.

After LowLatencyCanvasView.commit is called, the overlay is hidden and the buffer is drawn within the View hierarchy, similar to traditional View implementations.

A common use case would be a drawing application that intends to minimize the amount of latency when content is drawn with a stylus. In this case, touch events between MotionEvent.ACTION_DOWN and MotionEvent.ACTION_MOVE can trigger calls to LowLatencyCanvasView.renderFrontBufferedLayer which will minimize the delay between then the content is visible on screen. Finally when the gesture is complete on MotionEvent.ACTION_UP, a call to LowLatencyCanvasView.commit would be invoked to hide the transient overlay and render the scene within the View hierarchy like a traditional View. This helps provide a balance of low latency guarantees while mitigating potential tearing artifacts.

This helps support low latency rendering for simpler use cases at the expensive of configuration customization of the multi buffered layer content.

import androidx.annotation.WorkerThread
import androidx.graphics.lowlatency.LowLatencyCanvasView

LowLatencyCanvasView(context).apply {
    setBackgroundColor(Color.WHITE)

    data class Line(
        val x1: Float,
        val y1: Float,
        val x2: Float,
        val y2: Float,
    )
    // Thread safe collection to support creation of new lines from the UI thread as well as
    // consumption of lines from the background drawing thread
    val lines = Collections.synchronizedList(ArrayList<Line>())
    setRenderCallback(object : LowLatencyCanvasView.Callback {

        val mAllLines = ArrayList<Line>()

        private val mPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
            strokeWidth = 15f
            color = Color.CYAN
            alpha = 128
        }

        @WorkerThread
        override fun onRedrawRequested(
            canvas: Canvas,
            width: Int,
            height: Int
        ) {
            for (line in mAllLines) {
                canvas.drawLine(line.x1, line.y1, line.x2, line.y2, mPaint)
            }
        }

        @WorkerThread
        override fun onDrawFrontBufferedLayer(
            canvas: Canvas,
            width: Int,
            height: Int
        ) {
            lines.removeFirstOrNull()?.let { line ->
                mAllLines.add(line)
                canvas.drawLine(line.x1, line.y1, line.x2, line.y2, mPaint)
            }
        }
    })
    setOnTouchListener(object : View.OnTouchListener {

        var mCurrentX = -1f
        var mCurrentY = -1f
        var mPreviousX = -1f
        var mPreviousY = -1f

        override fun onTouch(v: View?, event: MotionEvent?): Boolean {
            if (event == null) return false
            when (event.action) {
                MotionEvent.ACTION_DOWN -> {
                    requestUnbufferedDispatch(event)
                    mCurrentX = event.x
                    mCurrentY = event.y
                }
                MotionEvent.ACTION_MOVE -> {
                    mPreviousX = mCurrentX
                    mPreviousY = mCurrentY
                    mCurrentX = event.x
                    mCurrentY = event.y

                    val line = Line(mPreviousX, mPreviousY, mCurrentX, mCurrentY)
                    lines.add(line)
                    renderFrontBufferedLayer()
                }
                MotionEvent.ACTION_CANCEL -> {
                    cancel()
                }
                MotionEvent.ACTION_UP -> {
                    commit()
                }
            }
            return true
        }
    })
}

Summary

Nested types
`public interface LowLatencyCanvasView.Callback` Provides callbacks for consumers to draw into the front buffered overlay as well as provide opportunities to synchronize `SurfaceControlCompat.Transaction`s to submit the layers to the hardware compositor

Public constructors
`LowLatencyCanvasView( @NonNull Context context, AttributeSet attrs, int defStyle )`

Public methods
`void`	`addView(View child)`
`void`	`addView(View child, int index)`
`void`	`addView(View child, ViewGroup.LayoutParams params)`
`void`	`addView(View child, int index, ViewGroup.LayoutParams params)`
`void`	`addView(View child, int width, int height)`
`final void`	`cancel()` Cancels any in progress request to render to the front buffer and hides the front buffered overlay.
`final void`	`clear()` Clears the content of the buffer and hides the front buffered overlay.
`final void`	`commit()` Invalidates this View and draws the buffer within View#onDraw.
`final void`	`execute(@NonNull Runnable runnable)` Dispatches a runnable to be executed on the background rendering thread.
`final void`	`renderFrontBufferedLayer()` Render content to the front buffered layer.
`final void`	`setRenderCallback(LowLatencyCanvasView.Callback callback)` Configures the `Callback` used to render contents to the front buffered overlay as well as optionally configuring the `SurfaceControlCompat.Transaction` used to update contents on screen.

Protected methods
`void`	`onAttachedToWindow()`
`void`	`onDraw(@NonNull Canvas canvas)`
`void`	`onLayout(boolean changed, int l, int t, int r, int b)`

Inherited methods

From android.view.View

`void`	`addFocusables(@NonNull ArrayList<@NonNull View> p0, int p1)`
`void`	`addOnAttachStateChangeListener( @NonNull View.OnAttachStateChangeListener p0 )`
`void`	`addOnLayoutChangeListener(@NonNull View.OnLayoutChangeListener p0)`
`void`	`addOnUnhandledKeyEventListener( @NonNull View.OnUnhandledKeyEventListener p0 )`
`@NonNull ViewPropertyAnimator`	`animate()`
`void`	`announceForAccessibility(@NonNull CharSequence p0)` This method is deprecated. Deprecated in Java
`void`	`autofill(@NonNull AutofillValue p0)`
`void`	`autofill(@NonNull SparseArray<@NonNull AutofillValue> p0)`
`boolean`	`awakenScrollBars()`
`boolean`	`awakenScrollBars(int p0)`
`boolean`	`awakenScrollBars(int p0, boolean p1)`
`void`	`bringToFront()`
`void`	`buildDrawingCache()` This method is deprecated. Deprecated in Java
`void`	`buildDrawingCache(boolean p0)` This method is deprecated. Deprecated in Java
`void`	`buildLayer()`
`boolean`	`callOnClick()`
`boolean`	`canResolveLayoutDirection()`
`boolean`	`canResolveTextAlignment()`
`boolean`	`canResolveTextDirection()`
`boolean`	`canScrollHorizontally(int p0)`
`boolean`	`canScrollVertically(int p0)`
`final void`	`cancelDragAndDrop()`
`void`	`cancelLongPress()`
`final void`	`cancelPendingInputEvents()`
`boolean`	`checkInputConnectionProxy(@NonNull View p0)`
`void`	`clearAnimation()`
`void`	`clearPendingCredentialRequest()`
`void`	`clearViewTranslationCallback()`
`int`	`computeHorizontalScrollExtent()`
`int`	`computeHorizontalScrollOffset()`
`int`	`computeHorizontalScrollRange()`
`void`	`computeScroll()`
`@NonNull WindowInsets`	`computeSystemWindowInsets(@NonNull WindowInsets p0, @NonNull Rect p1)`
`int`	`computeVerticalScrollExtent()`
`int`	`computeVerticalScrollOffset()`
`int`	`computeVerticalScrollRange()`
`@NonNull AccessibilityNodeInfo`	`createAccessibilityNodeInfo()`
`void`	`createContextMenu(@NonNull ContextMenu p0)`
`void`	`destroyDrawingCache()` This method is deprecated. Deprecated in Java
`boolean`	`dispatchGenericMotionEvent(@NonNull MotionEvent p0)`
`boolean`	`dispatchNestedFling(float p0, float p1, boolean p2)`
`boolean`	`dispatchNestedPreFling(float p0, float p1)`
`boolean`	`dispatchNestedPrePerformAccessibilityAction(int p0, @Nullable Bundle p1)`
`boolean`	`dispatchNestedPreScroll( int p0, int p1, @Nullable int[] p2, @Nullable int[] p3 )`
`boolean`	`dispatchNestedScroll(int p0, int p1, int p2, int p3, @Nullable int[] p4)`
`boolean`	`dispatchPopulateAccessibilityEvent(@NonNull AccessibilityEvent p0)`
`void`	`draw(@NonNull Canvas p0)`
`void`	`drawableHotspotChanged(float p0, float p1)`
`final @Nullable OnBackInvokedDispatcher`	`findOnBackInvokedDispatcher()`
`final @NonNull T`	`<T extends View> findViewById(int p0)`
`final @NonNull T`	`<T extends View> findViewWithTag(@NonNull Object p0)`
`boolean`	`fitSystemWindows(@NonNull Rect p0)` This method is deprecated. Deprecated in Java
`@NonNull View`	`focusSearch(int p0)`
`void`	`forceHasOverlappingRendering(boolean p0)`
`void`	`forceLayout()`
`void`	`generateDisplayHash( @NonNull String p0, @Nullable Rect p1, @NonNull Executor p2, @NonNull DisplayHashResultCallback p3 )`
`@NonNull View.AccessibilityDelegate`	`getAccessibilityDelegate()`
`int`	`getAccessibilityLiveRegion()`
`@NonNull AccessibilityNodeProvider`	`getAccessibilityNodeProvider()`
`@Nullable CharSequence`	`getAccessibilityPaneTitle()`
`int`	`getAccessibilityTraversalAfter()`
`int`	`getAccessibilityTraversalBefore()`
`@Nullable String`	`getAllowedHandwritingDelegatePackageName()`
`@Nullable String`	`getAllowedHandwritingDelegatorPackageName()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getAlpha()`
`@NonNull Animation`	`getAnimation()`
`@Nullable Matrix`	`getAnimationMatrix()`
`@NonNull IBinder`	`getApplicationWindowToken()`
`@NonNull int[]`	`getAttributeResolutionStack(int p0)`
`@NonNull Map<@NonNull Integer, @NonNull Integer>`	`getAttributeSourceResourceMap()`
`@Nullable String[]`	`@ViewDebug.ExportedProperty getAutofillHints()`
`final @NonNull AutofillId`	`getAutofillId()`
`int`	`getAutofillType()`
`@Nullable AutofillValue`	`getAutofillValue()`
`@NonNull Drawable`	`getBackground()`
`@Nullable BlendMode`	`getBackgroundTintBlendMode()`
`@Nullable ColorStateList`	`getBackgroundTintList()`
`@Nullable PorterDuff.Mode`	`getBackgroundTintMode()`
`int`	`@ViewDebug.ExportedProperty(category = "layout") getBaseline()`
`final int`	`@ViewDebug.CapturedViewProperty getBottom()`
`float`	`getBottomFadingEdgeStrength()`
`int`	`getBottomPaddingOffset()`
`float`	`getCameraDistance()`
`@NonNull Rect`	`getClipBounds()`
`boolean`	`getClipBounds(@NonNull Rect p0)`
`final boolean`	`getClipToOutline()`
`final @Nullable ContentCaptureSession`	`getContentCaptureSession()`
`@NonNull CharSequence`	`@ViewDebug.ExportedProperty(category = "accessibility") getContentDescription()`
`final int`	`getContentSensitivity()`
`final @NonNull Context`	`@ViewDebug.CapturedViewProperty getContext()`
`@NonNull ContextMenu.ContextMenuInfo`	`getContextMenuInfo()`
`final boolean`	`@ViewDebug.ExportedProperty(category = "focus") getDefaultFocusHighlightEnabled()`
`@NonNull Display`	`getDisplay()`
`final @NonNull int[]`	`getDrawableState()`
`@NonNull Bitmap`	`getDrawingCache()` This method is deprecated. Deprecated in Java
`@NonNull Bitmap`	`getDrawingCache(boolean p0)` This method is deprecated. Deprecated in Java
`int`	`getDrawingCacheBackgroundColor()` This method is deprecated. Deprecated in Java
`int`	`getDrawingCacheQuality()` This method is deprecated. Deprecated in Java
`void`	`getDrawingRect(@NonNull Rect p0)`
`long`	`getDrawingTime()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getElevation()`
`int`	`getExplicitStyle()`
`boolean`	`@ViewDebug.ExportedProperty getFilterTouchesWhenObscured()`
`boolean`	`@ViewDebug.ExportedProperty getFitsSystemWindows()`
`int`	`@ViewDebug.ExportedProperty(mapping = [@ViewDebug.IntToString(from = 0, to = "NOT_FOCUSABLE"), @ViewDebug.IntToString(from = 1, to = "FOCUSABLE"), @ViewDebug.IntToString(from = 16, to = "FOCUSABLE_AUTO")], category = "focus") getFocusable()`
`@NonNull ArrayList<@NonNull View>`	`getFocusables(int p0)`
`void`	`getFocusedRect(@NonNull Rect p0)`
`@NonNull Drawable`	`getForeground()`
`int`	`getForegroundGravity()`
`@Nullable BlendMode`	`getForegroundTintBlendMode()`
`@Nullable ColorStateList`	`getForegroundTintList()`
`@Nullable PorterDuff.Mode`	`getForegroundTintMode()`
`float`	`getFrameContentVelocity()`
`final boolean`	`getGlobalVisibleRect(@NonNull Rect p0)`
`boolean`	`getGlobalVisibleRect(@NonNull Rect p0, @NonNull Point p1)`
`@NonNull Handler`	`getHandler()`
`float`	`getHandwritingBoundsOffsetBottom()`
`float`	`getHandwritingBoundsOffsetLeft()`
`float`	`getHandwritingBoundsOffsetRight()`
`float`	`getHandwritingBoundsOffsetTop()`
`int`	`getHandwritingDelegateFlags()`
`@Nullable Runnable`	`getHandwritingDelegatorCallback()`
`final boolean`	`getHasOverlappingRendering()`
`final int`	`@ViewDebug.ExportedProperty(category = "layout") getHeight()`
`void`	`getHitRect(@NonNull Rect p0)`
`int`	`getHorizontalFadingEdgeLength()`
`int`	`getHorizontalScrollbarHeight()`
`@Nullable Drawable`	`getHorizontalScrollbarThumbDrawable()`
`@Nullable Drawable`	`getHorizontalScrollbarTrackDrawable()`
`int`	`@ViewDebug.CapturedViewProperty getId()`
`int`	`@ViewDebug.ExportedProperty(category = "accessibility", mapping = [@ViewDebug.IntToString(from = 0, to = "auto"), @ViewDebug.IntToString(from = 1, to = "yes"), @ViewDebug.IntToString(from = 2, to = "no"), @ViewDebug.IntToString(from = 4, to = "noHideDescendants")]) getImportantForAccessibility()`
`int`	`@ViewDebug.ExportedProperty(mapping = [@ViewDebug.IntToString(from = 0, to = "auto"), @ViewDebug.IntToString(from = 1, to = "yes"), @ViewDebug.IntToString(from = 2, to = "no"), @ViewDebug.IntToString(from = 4, to = "yesExcludeDescendants"), @ViewDebug.IntToString(from = 8, to = "noExcludeDescendants")]) getImportantForAutofill()`
`int`	`@ViewDebug.ExportedProperty(mapping = [@ViewDebug.IntToString(from = 0, to = "auto"), @ViewDebug.IntToString(from = 1, to = "yes"), @ViewDebug.IntToString(from = 2, to = "no"), @ViewDebug.IntToString(from = 4, to = "yesExcludeDescendants"), @ViewDebug.IntToString(from = 8, to = "noExcludeDescendants")]) getImportantForContentCapture()`
`boolean`	`getKeepScreenOn()`
`@NonNull KeyEvent.DispatcherState`	`getKeyDispatcherState()`
`int`	`@ViewDebug.ExportedProperty(category = "accessibility") getLabelFor()`
`int`	`@ViewDebug.ExportedProperty(category = "drawing", mapping = [@ViewDebug.IntToString(from = 0, to = "NONE"), @ViewDebug.IntToString(from = 1, to = "SOFTWARE"), @ViewDebug.IntToString(from = 2, to = "HARDWARE")]) getLayerType()`
`int`	`@ViewDebug.ExportedProperty(category = "layout", mapping = [@ViewDebug.IntToString(from = 0, to = "RESOLVED_DIRECTION_LTR"), @ViewDebug.IntToString(from = 1, to = "RESOLVED_DIRECTION_RTL")]) getLayoutDirection()`
`@NonNull ViewGroup.LayoutParams`	`@ViewDebug.ExportedProperty(deepExport = true, prefix = "layout_") getLayoutParams()`
`final int`	`@ViewDebug.CapturedViewProperty getLeft()`
`float`	`getLeftFadingEdgeStrength()`
`int`	`getLeftPaddingOffset()`
`final boolean`	`getLocalVisibleRect(@NonNull Rect p0)`
`void`	`getLocationInSurface(@NonNull int[] p0)`
`void`	`getLocationInWindow(@NonNull int[] p0)`
`void`	`getLocationOnScreen(@NonNull int[] p0)`
`@NonNull Matrix`	`getMatrix()`
`final int`	`getMeasuredHeight()`
`final int`	`@ViewDebug.ExportedProperty(category = "measurement", flagMapping = [@ViewDebug.FlagToString(mask = -16777216, equals = 16777216, name = "MEASURED_STATE_TOO_SMALL")]) getMeasuredHeightAndState()`
`final int`	`getMeasuredState()`
`final int`	`getMeasuredWidth()`
`final int`	`@ViewDebug.ExportedProperty(category = "measurement", flagMapping = [@ViewDebug.FlagToString(mask = -16777216, equals = 16777216, name = "MEASURED_STATE_TOO_SMALL")]) getMeasuredWidthAndState()`
`int`	`getMinimumHeight()`
`int`	`getMinimumWidth()`
`int`	`getNextClusterForwardId()`
`int`	`getNextFocusDownId()`
`int`	`getNextFocusForwardId()`
`int`	`getNextFocusLeftId()`
`int`	`getNextFocusRightId()`
`int`	`getNextFocusUpId()`
`@NonNull View.OnFocusChangeListener`	`getOnFocusChangeListener()`
`int`	`getOutlineAmbientShadowColor()`
`@NonNull ViewOutlineProvider`	`getOutlineProvider()`
`int`	`getOutlineSpotShadowColor()`
`int`	`getOverScrollMode()`
`int`	`getPaddingBottom()`
`int`	`getPaddingEnd()`
`int`	`getPaddingLeft()`
`int`	`getPaddingRight()`
`int`	`getPaddingStart()`
`int`	`getPaddingTop()`
`final @NonNull ViewParent`	`getParent()`
`@NonNull ViewParent`	`getParentForAccessibility()`
`final @Nullable OutcomeReceiver<@NonNull GetCredentialResponse, @NonNull GetCredentialException>`	`getPendingCredentialCallback()`
`final @Nullable GetCredentialRequest`	`getPendingCredentialRequest()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getPivotX()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getPivotY()`
`@NonNull PointerIcon`	`getPointerIcon()`
`final @NonNull List<@NonNull Rect>`	`getPreferKeepClearRects()`
`@Nullable String[]`	`getReceiveContentMimeTypes()`
`float`	`getRequestedFrameRate()`
`@NonNull Resources`	`getResources()`
`final boolean`	`getRevealOnFocusHint()`
`final int`	`@ViewDebug.CapturedViewProperty getRight()`
`float`	`getRightFadingEdgeStrength()`
`int`	`getRightPaddingOffset()`
`@Nullable AttachedSurfaceControl`	`getRootSurfaceControl()`
`@NonNull View`	`getRootView()`
`@NonNull WindowInsets`	`getRootWindowInsets()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getRotation()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getRotationX()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getRotationY()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getScaleX()`
`float`	`@ViewDebug.ExportedProperty(category = "drawing") getScaleY()`
`int`	`getScrollBarDefaultDelayBeforeFade()`
`int`	`getScrollBarFadeDuration()`
`int`	`getScrollBarSize()`
`int`	`@ViewDebug.ExportedProperty(mapping = [@ViewDebug.IntToString(from = 0, to = "INSIDE_OVERLAY"), @ViewDebug.IntToString(from = 16777216, to = "INSIDE_INSET"), @ViewDebug.IntToString(from = 33554432, to = "OUTSIDE_OVERLAY"), @ViewDebug.IntToString(from = 50331648, to = "OUTSIDE_INSET")]) getScrollBarStyle()`
`int`

LowLatencyCanvasView

Summary

Nested types

Public constructors

Public methods

Protected methods

Inherited methods