This test app was built to demonstrate and help debug slow line rendering in Android 5.0+. Three circular buffers of 50 values get a new value every 100ms, fed by a background thread. Two graphs animate the arrival of new values by progressively shifting the entire graph to the left over the 100ms they have before a new value arrives. Re-drawing happens every 16ms for a ~60FPS view.
In total each graph draws 150 lines using hardware-accelerated canvas.drawLine in a custom view's onDraw. A separate background thread updates the list of line coordinates to draw so that drawLine has no extra work to do.
While this test case app performs acceptably well on a Snapdragon 805, as soon as more complex layouts are involved and graphs are placed eg. in a CardView, it falls on its face. Granted, there are more efficient ways to draw (eg. use a bitmap, scroll it across the canvas and only add the one new line at the end) but 300 straight lines should not bring a modern GPU to its knees.
Reasons for the apparent inefficiency and slow drawing performance are discussed in this StackOverflow question.
- Android SDK 27
- Android Build Tools v27.0.3
This app uses the Gradle build system. To build, issue gradlew build or open this project in Android Studio.