Blog Archives
OpenTK, entering the C# 3D world
I was amazed how short the source code can be to show complex moving objects. It does take a bit of research and the OpenTK library though. There are a lot of very good YouTube tutorials out there. Not necessarily about OpenTK, but plenty about OpenGL, which is what OpenTK is using.
I asked my daughters to draw some Minecraft style avatars with a simple icon editor. They had their fun and I got something to display in 3D. I stored three icon files (Freya.ico, Merlin.ico and Steve.ico) in a subfolder called ‘Resources’.
Change the file properties. ‘Build Action’ should be set to ‘None’, because you don’t have to compile these files. And you don’t want to copy the files each time you run the compiler. Simply set ‘Copy to Output Directory’ to ‘Copy if newer’.
The next step is to install and reference the OpenTK library (OpenTK, OpenTK.Compatibility and OpenTK.GLControl). Be aware that there is no real WPF support for OpenTK. You only host a Winform control within WPF. Therefore you should also reference “WindowsFormsIntegration”.
You can also open a pure OpenTK window. But it is impossible to add further WPF controls to the same window then. We are far away from programming games, so it is always a good option to leave the backdoor open for further WPF. You might want to add sliders to set angles and object positions.
Sorry for posting less for a while. I am working like a dog – leaving home at 6am and returning around 10pm during the week.
<Window x:Class="OpenTkControl.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:WinF="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"
xmlns:OpenTK="clr-namespace:OpenTK;assembly=OpenTK.GLControl"
Title="OpenTK Demo" Height="600" Width="800">
<DockPanel LastChildFill="True">
<WindowsFormsHost x:Name="WinFormsContainer" Background="Transparent" DockPanel.Dock="Top" >
<OpenTK:GLControl x:Name="OpenTkControl"
Paint="OpenTkControl_Paint" Dock="Fill" />
</WindowsFormsHost>
</DockPanel>
</Window>
using OpenTK;
using OpenTK.Graphics.OpenGL;
using System;
using System.Drawing;
using System.Windows;
using System.Windows.Threading;
namespace OpenTkControl {
public partial class MainWindow : Window {
private DispatcherTimer _Timer;
private DateTime _ProgramStartTime;
public MainWindow() {
InitializeComponent();
_ProgramStartTime = DateTime.Now;
_Timer = new DispatcherTimer(DispatcherPriority.Send);
_Timer.IsEnabled = true;
_Timer.Interval = new TimeSpan(0, 0, 0, 0, 30);
_Timer.Tick += OnTimer;
_Timer.Start();
} // constructor
void OnTimer(object sender, EventArgs e) {
OpenTkControl.Invalidate();
} //
private void OpenTkControl_Paint(object sender, System.Windows.Forms.PaintEventArgs e) {
GLControl lControl = OpenTkControl;
// Reset the depth and color buffer.
// We want to render a new world. We do not want to continue with a previous rendering.
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
// Create a projection matrix transforming camera space to raster space. (google for "view frustum")
// Which is like: Press the 3D world and make it flat like a pancake, so that it does fit on the 2D screen.
// All points between a distance of 1 and 1000 will be taken into account.
float lAngleView = 1.2f; // y direction (in radians)
float lAspectRatio = 4f / 3f; // width / height
float lDistanceToNearClipPlane = 1f;
float lDistanceToFarClipPlane = 1000f;
Matrix4 lPerspective = Matrix4.CreatePerspectiveFieldOfView(lAngleView, lAspectRatio, lDistanceToNearClipPlane, lDistanceToFarClipPlane);
GL.MatrixMode(MatrixMode.Projection); GL.LoadIdentity(); GL.LoadMatrix(ref lPerspective);
// camera setup
Vector3 lCameraLocation = new Vector3(100f, 10f, 0f);
Vector3 lCameraLookingAt = new Vector3(0f, 0f, 0f); // look at the center of the coordinate system
Vector3 lCameraWhatIsUpside = new Vector3(0f, 1f, 0f); // classical way to hold a camera
Matrix4 lCamera = Matrix4.LookAt(lCameraLocation, lCameraLookingAt, lCameraWhatIsUpside);
GL.MatrixMode(MatrixMode.Modelview); GL.LoadIdentity(); GL.LoadMatrix(ref lCamera);
// this is the size on the screen
GL.Viewport(0, 0, lControl.Width, lControl.Height);
// only draw the nearest pixels and not pixels that are actually hidden by other pixels
GL.Enable(EnableCap.DepthTest);
GL.DepthFunc(DepthFunction.Less);
// set time dependent variables to generate movements
double lTotalMillis = DateTime.Now.Subtract(_ProgramStartTime).TotalMilliseconds;
double lTime1 = (lTotalMillis % 10000.0) / 10000.0; // between 0 and 1
double lTime2 = (lTotalMillis % 2000.0) / 2000.0; // between 0 and 1
double lTimeRadians = lTime2 * 2.0 * Math.PI;
float lJump = (float)(-20.0 + 10.0 * Math.Sin(lTimeRadians));
float lRadius = -40f;
// add the comet
DrawComet(lTotalMillis);
// render the floor
GL.Rotate(360.0 * lTime1, 0.0, 1.0, 0.5); // rotate around y axis and half as much around z axis
DrawFloor();
// render objects
// from where we are; now rotate the objects into the opposite direction
GL.Rotate(-lTime1 * 360.0 * 2.0, 0.0, 1.0, 0.0); DrawAvatar("Merlin", -30f, lRadius);
GL.Rotate(60.0, 0.0, 1.0, 0.0); DrawAvatar("Freya", lJump, lRadius);
GL.Rotate(60.0, 0.0, 1.0, 0.0); DrawAvatar("Steve", -30f, lRadius);
GL.Rotate(60.0, 0.0, 1.0, 0.0); DrawAvatar("Merlin", lJump, lRadius);
GL.Rotate(60.0, 0.0, 1.0, 0.0); DrawAvatar("Freya", -30f, lRadius);
GL.Rotate(60.0, 0.0, 1.0, 0.0); DrawAvatar("Steve", lJump, lRadius);
// render the cube in the center
//GL.Rotate(360f * lTime2, 0f, 0f, 0f); // <= this kind of rotation lets the box bounce and change its size
DrawCube(Color.SteelBlue, Color.DarkBlue, 0f, -25f, 0f, 8f, false);
OpenTK.Graphics.GraphicsContext.CurrentContext.VSync = true; // caps GPU frame rate
lControl.SwapBuffers(); // display our newly generated buffer with all objects
} //
private void DrawAvatar(string xName, float yShift, float zShift) {
Icon lIcon = new Icon("Resources/" + xName + ".ico");
Bitmap lBitmap = lIcon.ToBitmap();
int lWidth = lBitmap.Width; float lHalfWidth = lWidth / 2f;
int lHeight = lBitmap.Height; float lHalfHeight = lHeight;
for (int y = 0; y < lHeight; y++) {
for (int x = 0; x < lWidth; x++) {
Color lColor = lBitmap.GetPixel(x, y);
if (lColor.A != 0) DrawCube(lColor, lColor, (float)x - lHalfWidth, lHeight + yShift - (float)y, (float)zShift, 1f, true);
}
}
} //
private void DrawFloor() {
for (int x = -100; x < 100; x += 10) {
for (int z = -100 + (x % 10 == 0 ? 5 : 0); z < 100; z += 10) {
DrawCube(Color.White, Color.Gray, x, -30f, z, 5f, false);
}
}
} //
private void DrawComet(double xTotalMillis) {
xTotalMillis = (xTotalMillis % 7000.0) / 7000.0; // between 0 and 1
GL.PushMatrix();
GL.LoadIdentity();
GL.Translate(xTotalMillis * 30f - 40f , 40f, 400f * xTotalMillis - 400f);
GL.Rotate(360f * xTotalMillis * 3f, 1f, 1f, 1f);
DrawTetrahedron(Color.Orange, Color.OrangeRed, 0f, 0f, 0f, 8f);
GL.Rotate(180f, 1f, 0f, 0f);
DrawTetrahedron(Color.Orange, Color.OrangeRed, 0f, 0f, 0f, 8f);
GL.PopMatrix();
} //
private void DrawCube(System.Drawing.Color xColor, System.Drawing.Color xColor2, float X, float Y, float Z, float xWidth, bool xHasDarkBack) {
float lHalfWidth = xWidth / 2f;
float lTop = Y + lHalfWidth;
float lBottom = Y - lHalfWidth;
float lLeft = X - lHalfWidth;
float lRight = X + lHalfWidth;
float lFront = Z + lHalfWidth;
float lRear = Z - lHalfWidth;
GL.Begin(PrimitiveType.Quads);
Color lColor; if (xHasDarkBack) lColor = Color.DarkGray; else lColor = xColor;
Color lColor2; if (xHasDarkBack) lColor2 = Color.DarkGray; else lColor2 = xColor2;
Action lPointFrontTopLeft = () => { GL.Color3(xColor); GL.Vertex3(lLeft, lTop, lFront); };
Action lPointFrontTopRight = () => { GL.Color3(xColor2); GL.Vertex3(lRight, lTop, lFront); };
Action lPointFrontBottomLeft = () => { GL.Color3(xColor2); GL.Vertex3(lLeft, lBottom, lFront); };
Action lPointFrontBottomRight = () => { GL.Color3(xColor2); GL.Vertex3(lRight, lBottom, lFront); };
Action lPointRearTopLeft = () => { GL.Color3(lColor); GL.Vertex3(lLeft, lTop, lRear); };
Action lPointRearTopRight = () => { GL.Color3(lColor2); GL.Vertex3(lRight, lTop, lRear); };
Action lPointRearBottomLeft = () => { GL.Color3(lColor2); GL.Vertex3(lLeft, lBottom, lRear); };
Action lPointRearBottomRight = () => { GL.Color3(lColor2); GL.Vertex3(lRight, lBottom, lRear); };
// front square
lPointFrontTopLeft(); lPointFrontTopRight(); lPointFrontBottomRight(); lPointFrontBottomLeft();
// rear square
lPointRearTopLeft(); lPointRearTopRight(); lPointRearBottomRight(); lPointRearBottomLeft();
// top square
lPointFrontTopLeft(); lPointFrontTopRight(); lPointRearTopRight(); lPointRearTopLeft();
// bottom square
lPointFrontBottomLeft(); lPointFrontBottomRight(); lPointRearBottomRight(); lPointRearBottomLeft();
// left square
lPointFrontTopLeft(); lPointRearTopLeft(); lPointRearBottomLeft(); lPointFrontBottomLeft();
// right square
lPointFrontTopRight(); lPointRearTopRight(); lPointRearBottomRight(); lPointFrontBottomRight();
GL.End();
} //
private void DrawTetrahedron(System.Drawing.Color xColor, System.Drawing.Color xColor2, float X, float Y, float Z, float xSideLength) {
float lDistMidToVertex = (float)Math.Sqrt(6.0) / 4f * xSideLength;
float lDistMidToFloor = (float)Math.Sqrt(6.0) / 12f * xSideLength;
float lHeight = (float)Math.Sqrt(2.0 / 3.0) * xSideLength; // = lDistMidToVertex + lDistMidToEdge
float lTop = Y + lDistMidToVertex;
float lBottom = Y - lDistMidToFloor;
float lRight = X + xSideLength / 2f;
float lLeft = X - xSideLength / 2f;
float lRear = Z - (float) (xSideLength * Math.Sqrt(3.0) / 3.0);
float lFront = Z + (float)(xSideLength * Math.Sqrt(3.0) / 6.0);
GL.Begin(PrimitiveType.Triangles);
Action lPointTop = () => { GL.Color3(xColor); GL.Vertex3(X, lTop, Z); };
Action lPointFrontBottomLeft = () => { GL.Color3(xColor2); GL.Vertex3(lLeft, lBottom, lFront); };
Action lPointFrontBottomRight = () => { GL.Color3(xColor); GL.Vertex3(lRight, lBottom, lFront); };
Action lPointRear = () => { GL.Color3(xColor2); GL.Vertex3(X, lBottom, lRear); };
// front triangle
lPointTop(); lPointFrontBottomLeft(); lPointFrontBottomRight();
// left triangle
lPointTop(); lPointFrontBottomLeft(); lPointRear();
// right triangle
lPointTop(); lPointFrontBottomRight(); lPointRear();
// bottom triangle
lPointFrontBottomLeft(); lPointFrontBottomRight(); lPointRear();
GL.End();
} //
} // class
} // namespace
Slogan / News Ticker / Scrolling Text in WPF (Part 2)
This is the follow-up of my last post.
I promised to enhance the scroll behavior. Here it is. You can influence the text in various ways. When the zoom factor turns negative you can even see upside down characters. Also the drift can turn negative; if so the wave moves to the left, but its peaks drift to the right.
Weirdly enough it is a lot of fun playing with the sliders and watching the wave change. Of course, we could still create far more complex movements. This source code here is providing the full basics. The rest is up to you.
What you can influence:
- text zoom (negative numbers turn the text upside down)
- scroll speed
- wave amplitude
- wave drift
- wave length
I had to slightly change the way the vectors are stored to enable zooming. The y-zero-line now is in the middle of the characters and not at the top anymore. Anything above that line is negative, anything below positive. Hence the vectors can be multiplied with a zoom factor without the need to recalculate the position in the WPF control.
<Window x:Class="Ticker.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Ticker"
Height="250"
Width="500"
Loaded="Window_Loaded">
<DockPanel x:Name="MyDockPanel"
SizeChanged="MyImage_SizeChanged"
LastChildFill="True">
<Grid DockPanel.Dock="Top">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="110"/>
<ColumnDefinition Width="50*"/>
<ColumnDefinition Width="110"/>
<ColumnDefinition Width="50*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Label Content="calculation speed" Grid.Row="0"
HorizontalAlignment="Right" Padding="0,0,0,0"/>
<TextBox Name="Info"
Grid.Row="0" Grid.Column="1"/>
<Label Content="zoom" Grid.Row="0" Grid.Column="2"
HorizontalAlignment="Right" Padding="0,0,0,0"/>
<Slider Minimum="-1.0" Maximum="1.0" Value="1.0"
ValueChanged="Slider_Zoom_ValueChanged"
Grid.Row="0" Grid.Column="3" />
<Label Content="scroll speed" Grid.Row="1" Grid.Column="0"
HorizontalAlignment="Right" Padding="0,0,0,0"/>
<Slider Minimum="0.5" Maximum="8.0" Value="2.0"
ValueChanged="Slider_ScrollSpeed_ValueChanged"
Grid.Row="1" Grid.Column="1" />
<Label Content="wave amplitude" Grid.Row="1" Grid.Column="2"
HorizontalAlignment="Right" Padding="0,0,0,0"/>
<Slider Minimum="0.0" Maximum="100.0" Value="50.0"
ValueChanged="Slider_Amplitude_ValueChanged"
Grid.Row="1" Grid.Column="3" />
<Label Content="wave drift" Grid.Row="2" Grid.Column="0"
HorizontalAlignment="Right" Padding="0,0,0,0"/>
<Slider Minimum="-10.0" Maximum="10.0" Value="5.0"
ValueChanged="Slider_Drift_ValueChanged"
Grid.Row="2" Grid.Column="1" />
<Label Content="wave length" Grid.Row="2" Grid.Column="2"
HorizontalAlignment="Right" Padding="0,0,0,0"/>
<Slider Minimum="0.0" Maximum="2.0" Value="0.5"
ValueChanged="Slider_WaveLength_ValueChanged"
Grid.Row="2" Grid.Column="3" />
</Grid>
<Image Name="MyImage"
DockPanel.Dock="Top"
Stretch="None"
Width="{Binding ActualWidth, ElementName=MyDockPanel}"/>
</DockPanel>
</Window>
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Drawing;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media.Imaging;
using System.Windows.Threading;
namespace Ticker {
public partial class MainWindow : Window {
private Thread _Thread;
private TextEngine _TextEngine = new TextEngine();
private float _WidthInPixels;
private double _Speed = 1.0; // number of pixels to shift per iteration
private AutoResetEvent _AutoResetEvent = new AutoResetEvent(true);
private BitmapImage _BitmapImage = null;
private string _ElapsedTime = string.Empty;
public MainWindow() {
InitializeComponent();
} // constructor
private void Window_Loaded(object sender, EventArgs e) {
DataContext = this;
_Thread = new Thread(Loop);
_Thread.Name = "MainLoop";
_Thread.IsBackground = true;
_Thread.Priority = ThreadPriority.AboveNormal;
_Thread.Start();
TimeSpan lInterval = new TimeSpan(0, 0, 0, 0, 50); // run each 50 ms
EventHandler lHandler = new EventHandler(OnTime);
DispatcherTimer lDispatcherTimer = new DispatcherTimer(lInterval, DispatcherPriority.Send, lHandler, this.Dispatcher);
} //
private void MyImage_SizeChanged(object sender, SizeChangedEventArgs e) {
DockPanel lDockPanel = sender as DockPanel;
if (lDockPanel == null) return;
using (var lGraphics = Graphics.FromHwnd(IntPtr.Zero)) {
_WidthInPixels = (float)(e.NewSize.Width * lGraphics.DpiX / 96.0);
}
} //
public void OnTime(object XSender, EventArgs e) {
BitmapImage lBitmapImage = _BitmapImage;
if (lBitmapImage == null) return;
MyImage.Source = lBitmapImage;
Line.adjustDrift();
Info.Text = _ElapsedTime;
_AutoResetEvent.Set();
} //
private void Loop() {
float lEnd = 0f;
int lSectionFrom = 0;
int lSectionTo = 0;
Stopwatch lStopwatch = new Stopwatch();
while (true) {
_AutoResetEvent.WaitOne();
lStopwatch.Restart();
float lWidthInPixel = _WidthInPixels; // copy the value to avoid changes during the calculation
if (lWidthInPixel <= 0.0) continue;
List<Line> lSection = _TextEngine.getVectorSection(ref lSectionFrom, ref lSectionTo, lEnd, lWidthInPixel);
// This value determines the speed.
// Even numbers give better results due to the rounding error nature of bitmaps.
// Odd numbers create jitter. Luckily humans have bad eyes, they cannot perceive it.
lEnd += (float)_Speed;
if (lSection == null) {
// end reached, reset text
lSectionFrom = 0;
lSectionTo = 0;
lEnd = 0f;
}
else {
Bitmap lBitmap = _TextEngine.VectorsToBitmap(lSection, lWidthInPixel);
_BitmapImage = _TextEngine.BitmapToImageSource(lBitmap);
}
_ElapsedTime = lStopwatch.ElapsedMilliseconds.ToString("#,##0");
//lStopwatch.Stop();
}
} //
private void Slider_ScrollSpeed_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) { _Speed = e.NewValue; }
private void Slider_Amplitude_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) { Line.Amplitude = (float)e.NewValue; }
private void Slider_Drift_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) { Line.Drift = (float)e.NewValue; }
private void Slider_WaveLength_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) { Line.WaveLength = (float)e.NewValue; }
private void Slider_Zoom_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) { Line.Zoom = (float)e.NewValue; }
} // class
} // namespace
using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Windows.Media.Imaging;
namespace Ticker {
public class TextEngine {
private const float cFontHeight = 40f;
private const string cText = @"Die Gedanken sind frei, wer kann sie erraten, sie fliegen vorbei wie nächtliche Schatten. Kein Mensch kann sie wissen, kein Jäger erschießen mit Pulver und Blei: Die Gedanken sind frei! Ich denke was ich will und was mich beglücket, doch alles in der Still', und wie es sich schicket. Mein Wunsch und Begehren kann niemand verwehren, es bleibet dabei: Die Gedanken sind frei! Und sperrt man mich ein im finsteren Kerker, das alles sind rein vergebliche Werke. Denn meine Gedanken zerreißen die Schranken und Mauern entzwei: Die Gedanken sind frei! Drum will ich auf immer den Sorgen entsagen und will mich auch nimmer mit Grillen mehr plagen. Man kann ja im Herzen stets lachen und scherzen und denken dabei: Die Gedanken sind frei! Ich liebe den Wein, mein Mädchen vor allen, sie tut mir allein am besten gefallen. Ich sitz nicht alleine bei meinem Glas Weine, mein Mädchen dabei: Die Gedanken sind frei!";
private List<Line> _TextAsVectorChain = new List<Line>();
private Font _Font = new Font("Arial", cFontHeight, System.Drawing.FontStyle.Bold, GraphicsUnit.Pixel);
public TextEngine() {
// convert the entire text to vectors
float lPosition = 0;
Dictionary<char, List<Line>> lVectorCache = new Dictionary<char, List<Line>>();
char[] lChars = cText.ToCharArray();
foreach (char lChar in lChars) {
if (lChar == ' ') lPosition += 10; // distance for an empty space character
else {
List<Line> lOneCharVectors;
if (!lVectorCache.TryGetValue(lChar, out lOneCharVectors)) {
Bitmap lBitmap = CharToBitmap(lChar);
lOneCharVectors = BitmapToVectors(lBitmap);
lVectorCache.Add(lChar, lOneCharVectors);
}
float lNewPosition = lPosition;
foreach (Line lLine in lOneCharVectors) {
Line lClone = lLine.Clone();
lClone.X += lPosition;
lNewPosition = lClone.X;
_TextAsVectorChain.Add(lClone);
}
lPosition = lNewPosition + 4; // 4 == space between two characters
}
}
} // constructor
// Convert a bitmap to an ImageSource.
// We can then display the result in the WPF Image element.
public BitmapImage BitmapToImageSource(Bitmap xBitmap) {
using (MemoryStream lMemoryStream = new MemoryStream()) {
xBitmap.Save(lMemoryStream, System.Drawing.Imaging.ImageFormat.Bmp);
lMemoryStream.Position = 0;
BitmapImage lBitmapImage = new BitmapImage();
lBitmapImage.BeginInit();
lBitmapImage.StreamSource = lMemoryStream;
lBitmapImage.CacheOption = BitmapCacheOption.OnLoad;
lBitmapImage.EndInit();
lBitmapImage.Freeze();
return lBitmapImage;
}
} //
// draw a single character into a bitmap
private Bitmap _Bitmap = null;
public Bitmap CharToBitmap(char xChar) {
_Bitmap = new Bitmap((int)(cFontHeight * 1.25f), (int)(cFontHeight * 1.25f));
using (Graphics lGraphics = Graphics.FromImage(_Bitmap)) {
lGraphics.Clear(Color.White);
lGraphics.DrawString(xChar.ToString(), _Font, Brushes.Black, 0f, 0f);
}
return _Bitmap;
} //
// Replicate the characters now by reading the vectors and drawing lines.
Pen lPen = new Pen(Color.Black, 2f);
public Bitmap VectorsToBitmap(List<Line> xLines, float xBitmapWidth) {
int lHeight = (int)cFontHeight + (int)Math.Abs(Line.Amplitude);
Bitmap lBitmap = new Bitmap((int)xBitmapWidth, lHeight);
lHeight /= 2; // half height, rounded down
using (Graphics lGraphics = Graphics.FromImage(lBitmap)) {
lGraphics.Clear(Color.White);
foreach (Line lLine in xLines) {
lGraphics.DrawLine(lPen, lLine.X, lLine.Y1 + lHeight, lLine.X, lLine.Y2 + lHeight);
}
}
return lBitmap;
} //
// Convert a single character to vectors.
private List<Line> BitmapToVectors(Bitmap xBitmap) {
int lXCoordinateOfFirstPixel = -1;
List<Line> lList = new List<Line>();
for (int x = 0, lWidth = xBitmap.Width; x < lWidth; x++) {
Line lVector = null;
for (int y = 0, lHeight = xBitmap.Height; y < lHeight; y++) {
Color lColor = xBitmap.GetPixel(x, y);
bool lIsWhite = lColor.B == 255;
if (lIsWhite) {
if (lVector != null) {
lList.Add(lVector);
lVector = null;
}
}
else {
int lHalfHeight = xBitmap.Height / 2;
if (lVector == null) {
if (lXCoordinateOfFirstPixel < 0) lXCoordinateOfFirstPixel = x; // to always start at zero for our vectors
lVector = new Line { X = x - lXCoordinateOfFirstPixel, Y1 = y - lHalfHeight, Y2 = y - lHalfHeight };
}
else lVector.Y2 = y - lHalfHeight;
}
}
}
return lList;
} //
// The text was converted to vectors.
// Now we cut out the sequence we need for the display.
internal List<Line> getVectorSection(ref int xSectionFrom, ref int xSectionTo, float xEnd, float xWidth) {
int lCount = _TextAsVectorChain.Count;
float lStart = xEnd - xWidth;
// find the right section
do {
xSectionTo++;
if (xSectionTo >= lCount) { xSectionTo = lCount - 1; break; }
if (xEnd < _TextAsVectorChain[xSectionTo].X) break;
} while (true);
do {
if (lStart < 0) break; // to allow empty spaces at the beginning of the slogan
if (xSectionFrom >= lCount) return null;
if (lStart < _TextAsVectorChain[xSectionFrom].X) break;
xSectionFrom++;
} while (true);
// clone that section
List<Line> lList = new List<Line>();
for (int x = xSectionFrom; x <= xSectionTo; x++) {
Line lClone = _TextAsVectorChain[x].Clone();
lClone.X -= lStart; // adjust the X-axis
lClone.RecalcYShift();
lList.Add(lClone);
}
return lList;
} //
} // class
} // namespace
using System;
namespace Ticker {
public class Line {
private float _Y1, _Y1Shift;
private float _Y2, _Y2Shift;
private static float _XDrift = 0f;
public float X { get; set; }
public static float Amplitude { get; set; } // This is the additional height needed for the vertical swing
public static float Drift { get; set; } // How fast does the wave crest/trough move?
public static float WaveLength { get; set; } // How wide is the wave?
public static float Zoom { get; set; } // Character zoom factor around the horizontal middle.
public static void adjustDrift() { _XDrift += Drift; }
public float Y1 {
get { return _Y1 * Zoom + _Y1Shift; }
set { _Y1 = value; }
} //
public float Y2 {
get { return _Y2 * Zoom + _Y2Shift; }
set { _Y2 = value; }
} //
public void RecalcYShift() {
double d = (double)(WaveLength * (X + _XDrift));
d = Math.IEEERemainder(d / 50.0, 1.99999999999);
float lAngle = (float)Math.Sin(Math.PI * d); // 0.0 <= d < 2.0 therefore -1.0 <= lAngle <= 1.0
float lShift = Amplitude / 2.0f * lAngle;
_Y1Shift = lShift;
_Y2Shift = lShift;
} //
public Line Clone() {
Line lLine = new Line();
lLine.X = X;
lLine.Y1 = _Y1;
lLine.Y2 = _Y2;
return lLine;
} //
} // class
} // namespace
Slogan / News Ticker / Scrolling Text in WPF
Oh, I used to write so called intros with scrolling text slogans at the bottom on the Commodore Amiga. The hardware was pretty much unalterable and you could easily work with the Blitter and Copper. The vertical blank beam on the monitor was my timer. These days are over. No more Assembler. And who cares about high and low byte these days?
I have to admit that using C# in combination with WPF is not the best approach for moving text around. You should directly talk to graphic cards for such. Anyway, it started with a short benchmark test and ended up with this example program. If you program properly, then you can make WPF do the job without any flickering.
You might wonder why my approach is quite indirect this time. I am not simply rendering text to the screen and then change its position. This program is slightly more complex. The reason is that I am planning a follow-up with more complex movements soon. I am planning to show you how to scroll text along the screen in a sinus curve while the curve itself behaves like a wave. Maybe I will add some topsy-turvy stuff as well. Hehe, it is not written yet.
This post is providing the basics to get prepared for the next step. Today, the text simply moves from the right to the left. And no worries about the end of the text. It is dealt with properly.
You can change the speed with the slider while the text field returns the calculation time in milliseconds. You can see that we still have some timing leeway. There are no issues with our frequency, which is 20 updates per second. The screen itself obviously updates more often. Its frequency has little to do with the one for showing new BitmapImages. Our thread loop takes less than 20 milliseconds.
How does the program work?
- A loop is running on an independent thread. This loop executes each time right after our WPF update. This well chosen moment avoids timing conflicts efficiently. The next BitmapImage is ready to be shown before the next WPF GUI update.
- At the beginning of the program we convert the entire text to vectors. The orientation of all vectors is vertical. Each x-value can consist of several vertical vectors. For instance the character “E” has 1 or 3 vertical vectors. The first vector is a straight vertical black line from the top to the bottom. When you are in the middle of the character, then you have three black and two white areas. We only convert the black parts. Imagine a vertical cut right through the middle from the top to the bottom.
- The conversion from “character to bitmap to vector” is NOT conducted in real-time. This is done during the program initialization as mentioned above. Only then we can run at full steam afterwards.
- We only change the precalculated vectors and render the bitmap in real-time – nothing else.
- These vectors are then drawn to bitmaps. These bitmaps are not dependent on the Dispatcher thread. We are still running at maximum speed. Before we can change the source for the Image control, we have to convert the Bitmap class to an ImageSource.
- This ImageSource is then assigned to the Image control during a DispatcherTimer event.
Once again the program was kept to a minimum length. Maybe I should have added some more classes. I hope I found the right length for this example program in the end.
This code was not straight forward. There had to be a learning curve … as usual. First, I tried some direct WPF binding. The timing was nearly out of control. So I gave up after a while. But I had some nice blog ideas in the meantime. We should enter the 3D world at some point, don’t you think so?
The 3D approach would most likely the best approach for our scrolling text as well. I expect the efficiency to be extreme. There are so many games with millions of mesh triangles rendered within milliseconds – this cannot be bad stuff. We could even use 3D features for showing 2D text.
This will surely require some profound research on my side. Don’t expect anything anytime soon. I am definitely not omniscient.
<Window x:Class="Ticker.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Ticker"
Height="130"
Width="400"
Loaded="Window_Loaded">
<StackPanel x:Name="MyStackPanel"
SizeChanged="MyImage_SizeChanged">
<DockPanel LastChildFill="True">
<Slider Width="300" DockPanel.Dock="Right"
Minimum="0.5" Maximum="8.0"
Value="2.0"
ValueChanged="Slider_ValueChanged" />
<TextBox Name="Info" DockPanel.Dock="Right"/>
</DockPanel>
<Image Name="MyImage"
Stretch="None"
Height="60"
Width="{Binding ActualWidth, ElementName=MyStackPanel}"/>
</StackPanel>
</Window>
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Drawing;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media.Imaging;
using System.Windows.Threading;
namespace Ticker {
public partial class MainWindow : Window {
private Thread _Thread;
private TextEngine _TextEngine = new TextEngine();
private float _WidthInPixels;
private double _Speed = 1.0; // number of pixels to shift per iteration
private AutoResetEvent _AutoResetEvent = new AutoResetEvent(true);
private BitmapImage _BitmapImage = null;
private string _ElapsedTime = string.Empty;
public MainWindow() {
InitializeComponent();
} // constructor
private void Window_Loaded(object sender, EventArgs e) {
DataContext = this;
_Thread = new Thread(Loop);
_Thread.Name = "MainLoop";
_Thread.IsBackground = true;
_Thread.Priority = ThreadPriority.AboveNormal;
_Thread.Start();
TimeSpan lInterval = new TimeSpan(0, 0, 0, 0, 50); // run each 50 ms
EventHandler lHandler = new EventHandler(OnTime);
DispatcherTimer lDispatcherTimer = new DispatcherTimer(lInterval, DispatcherPriority.Send, lHandler, this.Dispatcher);
} //
private void MyImage_SizeChanged(object sender, SizeChangedEventArgs e) {
StackPanel lStackPanel = sender as StackPanel;
if (lStackPanel == null) return;
using (var lGraphics = Graphics.FromHwnd(IntPtr.Zero)) {
_WidthInPixels = (float)(e.NewSize.Width * lGraphics.DpiX / 96.0);
}
} //
public void OnTime(object XSender, EventArgs e) {
BitmapImage lBitmapImage = _BitmapImage;
if (lBitmapImage == null) return;
MyImage.Source = lBitmapImage;
Info.Text = _ElapsedTime;
_AutoResetEvent.Set();
} //
private void Loop() {
float lEnd = 0f;
int lSectionFrom = 0;
int lSectionTo = 0;
Stopwatch lStopwatch = new Stopwatch();
while (true) {
_AutoResetEvent.WaitOne();
lStopwatch.Restart();
float lWidthInPixel = _WidthInPixels; // copy the value to avoid changes during the calculation
if (lWidthInPixel <= 0.0) continue;
List<Line> lSection = _TextEngine.getVectorSection(ref lSectionFrom, ref lSectionTo, lEnd, lWidthInPixel);
// This value determines the speed.
// Even numbers give better results due to the rounding error nature of bitmaps.
// Odd numbers create jitter. Luckily humans have bad eyes, they cannot perceive it.
lEnd += (float)_Speed;
if (lSection == null) {
// end reached, reset text
lSectionFrom = 0;
lSectionTo = 0;
lEnd = 0f;
}
else {
Bitmap lBitmap = _TextEngine.VectorsToBitmap(lSection, lWidthInPixel);
_BitmapImage = _TextEngine.BitmapToImageSource(lBitmap);
}
_ElapsedTime = lStopwatch.ElapsedMilliseconds.ToString("#,##0");
lStopwatch.Stop();
}
} //
private void Slider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) {
_Speed = e.NewValue;
} //
} // class
} // namespace
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Windows.Media.Imaging;
namespace Ticker {
public class TextEngine {
private const string cText = @"Die Gedanken sind frei, wer kann sie erraten, sie fliegen vorbei wie nächtliche Schatten. Kein Mensch kann sie wissen, kein Jäger erschießen mit Pulver und Blei: Die Gedanken sind frei! Ich denke was ich will und was mich beglücket, doch alles in der Still', und wie es sich schicket. Mein Wunsch und Begehren kann niemand verwehren, es bleibet dabei: Die Gedanken sind frei! Und sperrt man mich ein im finsteren Kerker, das alles sind rein vergebliche Werke. Denn meine Gedanken zerreißen die Schranken und Mauern entzwei: Die Gedanken sind frei! Drum will ich auf immer den Sorgen entsagen und will mich auch nimmer mit Grillen mehr plagen. Man kann ja im Herzen stets lachen und scherzen und denken dabei: Die Gedanken sind frei! Ich liebe den Wein, mein Mädchen vor allen, sie tut mir allein am besten gefallen. Ich sitz nicht alleine bei meinem Glas Weine, mein Mädchen dabei: Die Gedanken sind frei!";
private List<Line> _TextAsVectorChain = new List<Line>();
public TextEngine() {
// convert the entire text to vectors
float lPosition = 0;
Dictionary<char, List<Line>> lVectorCache = new Dictionary<char, List<Line>>();
char[] lChars = cText.ToCharArray();
foreach (char lChar in lChars) {
if (lChar == ' ') lPosition += 10; // distance for an empty space character
else {
List<Line> lOneCharVectors;
if (!lVectorCache.TryGetValue(lChar, out lOneCharVectors)) {
Bitmap lBitmap = CharToBitmap(lChar);
lOneCharVectors = BitmapToVectors(lBitmap);
lVectorCache.Add(lChar, lOneCharVectors);
}
float lNewPosition = lPosition;
foreach (Line lLine in lOneCharVectors) {
Line lClone = lLine.Clone();
lClone.X += lPosition;
lNewPosition = lClone.X;
_TextAsVectorChain.Add(lClone);
}
lPosition = lNewPosition + 4; // 4 == space between two characters
}
}
} // constructor
// Convert a bitmap to an ImageSource.
// We can then display the result in the WPF Image element.
public BitmapImage BitmapToImageSource(Bitmap xBitmap) {
using (MemoryStream lMemoryStream = new MemoryStream()) {
xBitmap.Save(lMemoryStream, System.Drawing.Imaging.ImageFormat.Bmp);
lMemoryStream.Position = 0;
BitmapImage lBitmapImage = new BitmapImage();
lBitmapImage.BeginInit();
lBitmapImage.StreamSource = lMemoryStream;
lBitmapImage.CacheOption = BitmapCacheOption.OnLoad;
lBitmapImage.EndInit();
lBitmapImage.Freeze();
return lBitmapImage;
}
} //
// draw a single character into a bitmap
private Font _Font = null;
private Bitmap _Bitmap = null;
public Bitmap CharToBitmap(char xChar) {
if (_Font == null) {
_Font = new Font("Arial", 40.0f, System.Drawing.FontStyle.Bold, GraphicsUnit.Pixel);
_Bitmap = new Bitmap(60, 70);
}
using (Graphics lGraphics = Graphics.FromImage(_Bitmap)) {
lGraphics.Clear(Color.White);
lGraphics.DrawString(xChar.ToString(), _Font, Brushes.Black, 0f, 0f);
}
return _Bitmap;
} //
// Replicate the characters now by reading the vectors and drawing lines.
Pen lPen = new Pen(Color.Black, 2f);
public Bitmap VectorsToBitmap(List<Line> xLines, float xBitmapWidth) {
if (_Font == null) { _Font = new Font("Arial", 40.0f, System.Drawing.FontStyle.Bold, GraphicsUnit.Pixel); }
Bitmap lBitmap = new Bitmap((int)xBitmapWidth, 60);
using (Graphics lGraphics = Graphics.FromImage(lBitmap)) {
lGraphics.Clear(Color.White);
foreach (Line lLine in xLines) {
lGraphics.DrawLine(lPen, lLine.X, lLine.Y1, lLine.X, lLine.Y2);
}
}
return lBitmap;
} //
// Convert a single character to vectors.
private List<Line> BitmapToVectors(Bitmap xBitmap) {
int lXCoordinateOfFirstPixel = -1;
List<Line> lList = new List<Line>();
for (int x = 0, lWidth = xBitmap.Width; x < lWidth; x++) {
Line lVector = null;
for (int y = 0, lHeight = xBitmap.Height; y < lHeight; y++) {
Color lColor = xBitmap.GetPixel(x, y);
bool lIsWhite = lColor.B == 255;
if (lIsWhite) {
if (lVector != null) {
lList.Add(lVector);
lVector = null;
}
}
else {
if (lVector == null) {
if (lXCoordinateOfFirstPixel < 0) lXCoordinateOfFirstPixel = x; // to always start at zero for our vectors
lVector = new Line { X = x - lXCoordinateOfFirstPixel, Y1 = y, Y2 = y };
}
else lVector.Y2 = y;
}
}
}
return lList;
} //
// The text was converted to vectors.
// Now we cut out the sequence we need for the display.
internal List<Line> getVectorSection(ref int xSectionFrom, ref int xSectionTo, float xEnd, float xWidth) {
int lCount = _TextAsVectorChain.Count;
float lStart = xEnd - xWidth;
// find the right section
do {
xSectionTo++;
if (xSectionTo >= lCount) { xSectionTo = lCount - 1; break; }
if (xEnd < _TextAsVectorChain[xSectionTo].X) break;
} while (true);
do {
if (lStart < 0) break; // to allow empty spaces at the beginning of the slogan
if (xSectionFrom >= lCount) return null;
if (lStart < _TextAsVectorChain[xSectionFrom].X) break;
xSectionFrom++;
} while (true);
// clone that section
List<Line> lList = new List<Line>();
for (int x = xSectionFrom; x <= xSectionTo; x++) {
Line lClone = _TextAsVectorChain[x].Clone();
lClone.X -= lStart; // adjust the X-axis
lList.Add(lClone);
}
return lList;
} //
} // class
} // namespace
namespace Ticker {
public class Line {
public float X { get; set; }
public float Y1 { get; set; }
public float Y2 { get; set; }
public Line Clone() {
Line lLine = new Line();
lLine.X = X;
lLine.Y1 = Y1;
lLine.Y2 = Y2;
return lLine;
} //
} // class
} // namespace
migration C#, Java, C++ (day 11), future and promise
There is hardly anything directly to compare with in C#. Future and promise are C++ concepts, which are probably best compared to C# task concepts. The comparison was not easy today. Have a look at the outcome.
future and promise
using System;
using System.Threading;
using System.Threading.Tasks;
namespace Program {
public class Day11 {
private class Params {
public int Input;
public int Result;
}
private void DoSomething() {
Console.WriteLine("DoSomething()");
Thread.Sleep(4000);
} //
private void Method1(object xObject) {
Params lParams = xObject as Params;
Console.WriteLine("Method1");
Thread.Sleep(2000);
lParams.Result = 2 * lParams.Input;
} //
private int Method2(int xInt1) {
Console.WriteLine("Method2");
Thread.Sleep(2000);
return 2 * xInt1;
} //
private async Task<int> Method3(int xInt1) {
await Task.Delay(0);
Console.WriteLine("Method3");
return 2 * xInt1;
} //
private void Method4(Params xParams, AutoResetEvent xEvent) {
Console.WriteLine("Method4");
Thread.Sleep(2000);
xEvent.WaitOne();
xParams.Result = 2 * xParams.Input;
} //
static void Main(string[] args) {
Day11 lDay10 = new Day11();
lDay10.test();
} //
public async void test() {
int i;
// use a thread to get an asynchronous result
ParameterizedThreadStart lParams = new ParameterizedThreadStart(Method1);
Thread thread1 = new Thread(lParams);
Params p = new Params() { Input = 123 };
thread1.Start(p);
Console.WriteLine("Method1.join()");
thread1.Join();
Console.WriteLine("Method1 result is: " + p.Result);
Func<int, int> t1 = new Func<int, int>(x => { return Method2(x); });
i = t1(123); // synchronous
IAsyncResult lResult = t1.BeginInvoke(123, null, null); // asynchronously
lResult.AsyncWaitHandle.WaitOne();
i = await Method3(123);
Console.WriteLine("Method3 result is: " + i);
p.Input = 123;
p.Result = 0;
AutoResetEvent lEvent = new AutoResetEvent(false);
Task t2 = new Task(() => Method4(p, lEvent));
t2.Start();
lEvent.Set();
t2.Wait();
Console.WriteLine("Method4 result is: " + p.Result);
Console.ReadLine();
} //
} // class
} // namespace
example output:
Method1.join()
Method1
Method1 result is: 246
Method2
Method2
Method3
Method3 result is: 246
Method4
Method4 result is: 246
#include <future>
#include <iostream>
#include <thread>
using namespace std;
void DoSomething() {
cout << "DoSomething()" << endl;
this_thread::sleep_for(chrono::seconds(4));
} //
void Thread1(int xInt1, int &xInt2) {
cout << "Thread1" << endl;
this_thread::sleep_for(chrono::seconds(2));
xInt2 = 2 * xInt1;
} //
int Thread2(int xInt1) {
cout << "Thread2" << endl;
this_thread::sleep_for(chrono::seconds(2));
return 2 * xInt1;
} //
int Thread3(future<int> &xInt1) {
cout << "Thread3" << endl;
this_thread::sleep_for(chrono::seconds(2));
return 2 * xInt1.get(); // .get() => waits until the promise is fullfilled
} //
int Thread4(shared_future<int> xInt1) {
cout << "Thread4" << endl;
this_thread::sleep_for(chrono::seconds(2));
return 2 * xInt1.get(); // returns the same value to all waiting futures
} //
void test(){
int i;
// use a thread to get an asynchronous result
thread t1(Thread1, 123, ref(i));
cout << "Thread1.join()" << endl;
t1.join();
cout << "Thread1 result is: " << i << endl;
// like a task, may be synchronous or asychronous
future<int> f1 = async(Thread2, 123);
cout << "Thread2, f1.get()" << endl;
i = f1.get(); // waits
// like a synchronous task, which is running on the same thread
// will be called when you get the value
future<int> f2 = async(launch::deferred, Thread2, 123);
cout << "Thread2, f2.get()" << endl;
i = f2.get(); // waits
cout << "Thread2 deferred result is: " << i << endl;
// like an asynchronous task, which is running on a new thread
future<int> f3 = async(launch::async, Thread2, 123);
cout << "Thread2, f3.get()" << endl;
i = f3.get(); // waits
cout << "Thread2 async result is: " << i << endl;
// same as f1, because this is the default value; the system decides what to do
future<int> f4 = async(launch::async | launch::deferred, Thread2, 123);
i = f4.get(); // waits
promise<int> lPromise5; // promise to provide a value at a later time
future<int> f5 = lPromise5.get_future();
future<int> f5b = async(launch::async, Thread3, ref(f5));
DoSomething();
cout << "lPromise5.set_value()" << endl;
lPromise5.set_value(123); // fulfill our promise now
cout << "f5b async result is: " << f5b.get() << endl;
promise<int> lPromise6; // promise to provide a value at a later time
future<int> f6 = lPromise6.get_future();
DoSomething();
// tell the parallel thread to stop waiting for the promise fulfillment
lPromise6.set_exception(make_exception_ptr(runtime_error("sorry, I cannot fulfill my promise")));
//
// SOME PRACTICAL ISSUES
//
promise<int> lPromise7; // promise to provide a value at a later time
future<int> f7 = lPromise7.get_future();
promise<int> lPromise8 = move(lPromise7); // you cannot assign a promise, you have to move it
future<int> f8 = move(f7); // same with the future
// you cannot call future.get() more than once
// to allow multiple consumers use:
shared_future<int> f9 = f8.share();
future<int> f10 = async(launch::async, Thread4, f9);
future<int> f11 = async(launch::async, Thread4, f9);
future<int> f12 = async(launch::async, Thread4, f9);
future<int> f13 = async(launch::async, Thread4, f9);
lPromise8.set_value(123);
cout << "f10: " << f10.get() << ", f11:" << f11.get() << ", f12:" << f12.get() << ", f13:" << f13.get() << endl;
// packaged_task
auto t2 = bind(Thread2, 123);
t2(); // synchronous
packaged_task<int()> t3(bind(Thread2, 123)); // wrapper to make async calls
t3(); // call the task in a different context
future<int> f14 = t3.get_future(); // getting a future is not possible with t2
int x = f14.get();
cout << "f14: " << x << endl;
cin.get();
} //
example output:
Thread1.join()
Thread1Thread1 result is: 246
Thread2, f1.get()
Thread2Thread2, f2.get()
Thread2
Thread2 deferred result is: 246
Thread2, f3.get()
Thread2Thread2 async result is: 246
Thread2
DoSomething()
Thread3lPromise5.set_value()
f5b async result is: 246
DoSomething()
Thread4
Thread4Thread4
Thread4
f10: 246, f11:246, f12:246, f13:246
Thread2
Thread2
f14: 246
package Program;
import java.util.*;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class Day11 {
private static void Sleep(int xMilliseconds) {
try {
Thread.sleep(xMilliseconds);
} catch (InterruptedException ex) {
System.err.println(ex.getMessage());
}
} //
private class Thread1 extends Thread {
public int Input;
public int Result;
@Override
public void run() {
System.out.println("Thread1");
Sleep(2000);
Result = 2 * Input;
} //
} // class
private class Thread2 {
private final ExecutorService pool = Executors.newFixedThreadPool(5);
public Future<Integer> getPromise(final int xInt1) {
return pool.submit(() -> {
System.out.println("Thread2");
Sleep(2000);
return 2 * xInt1;
});
} //
} // class
private class Thread3 implements Callable<Integer> {
private final ExecutorService _Pool = Executors.newFixedThreadPool(5);
private int _Int1;
public Future<Integer> getPromise(final int xInt1) {
_Int1 = xInt1;
return _Pool.submit(this);
} //
@Override
public Integer call() throws Exception {
synchronized (this) {
this.wait();
}
System.out.println("Thread3");
Sleep(2000);
return 2 * _Int1;
} //
} // class
public final void test() throws InterruptedException, ExecutionException {
// use a thread to get an asynchronous result
Thread1 t1 = new Thread1();
t1.Input = 123;
t1.start();
System.out.println("Thread1.join()");
t1.join();
System.out.println("Thread1 result is: " + t1.Result);
// like a task, may be synchronous or asychronous
Thread2 t2 = new Thread2();
Future<Integer> f1 = t2.getPromise(123);
System.out.println("Thread2, f1.getPromise(123)");
int i = f1.get(); // waits
System.out.println("f1 result is: " + i);
// deferred
Thread3 t3 = new Thread3();
Future<Integer> f2 = t3.getPromise(123);
synchronized (t3) {
t3.notify(); // start calculation manually
}
System.out.println("Thread3 result is: " + f2.get()); // wait
new Scanner(System.in).nextLine();
} //
public static void main(String[] args) throws InterruptedException, ExecutionException {
Day11 lDay11 = new Day11();
lDay11.test();
} //
} // class
example output:
Thread1
Thread1.join()
Thread1 result is: 246
Thread2
Thread2, f1.getPromise(123)
f1 result is: 246
Thread3
Thread3 result is: 246
Async and await (advanced, .Net 4.5, C# 5)
The importance is in the details. It all looks easy, but follow each step carefully today.
Windows pauses threads that are waiting for I/O operations to complete (eg. internet or file access). The same threads cannot be used for other jobs in the meantime and new threads need to be created. You could use tasks to solve this specific problem. The program would start an asynchronous task to deal with an I/O operation. After a while the same task would trigger a follow-up procedure via continuation task. It requires some work to cover all code paths, but it can be done.
C# 5 has implemented new keywords to make your life easier. You can use async to mark methods for asynchronous operations, which start synchronously and then split up as soon as the program arrives at any await keyword.
The below Print() method prints the time, sequence and ThreadId. This information is useful to understand the program cycle.
private static void Print(int xStep) {
Console.WriteLine(DateTime.Now.ToString("HH:mm:ss") + " step " + xStep + " , thread " + Thread.CurrentThread.ManagedThreadId);
} //
static async void AsyncCalls1() {
Print(1);
int i = await Task.Run<int>(() => {
Print(2); Thread.Sleep(5000);
Print(3); return 0;
});
Print(4); // same thread as in step 3
Console.ReadLine();
// return void
} //
example output:
19:09:36 step 1 , thread 9
19:09:36 step 2 , thread 10
19:09:41 step 3 , thread 10
19:09:41 step 4 , thread 10
The above code is a warm up for us. The method AsyncCalls1() returns void. I emphasize this seemingly insignificant fact here. If you do not return void then the compiler will complain. It wants you to add async in the calling method as well. But if you do so, then it would also ask you to add async in the calling method, that called the calling method. It would be an endless game until you arrive at Main(). And there you would not know what to do, because you cannot use async in Main(). Novices can get quite frustrated with such minuscule glitch.
What is the program doing? It starts new task, which uses another thread from the thread pool. The original thread is then neglected, there is no follow-up. Now check this out: When the created task ends, the program continues with (Task.ContinueWith()) the same thread, which it was using in the task. It seems there is no context switching.
static async void AsyncCalls2() {
Print(1); Task<int> task = AsyncCalls3();
Print(4); int x = await task;
Print(7); // same thread as in step 6
Console.ReadLine();
// return void
} //
static async Task<int> AsyncCalls3() {
Print(2);
int i = await Task.Run<int>(() => {
Print(3); Thread.Sleep(5000);
Print(5); return 0;
});
Print(6); return i; // same thread as in step 5, returning an INTEGER !!!
} //
example output:
19:10:16 step 1 , thread 9
19:10:16 step 2 , thread 9
19:10:16 step 3 , thread 10
19:10:16 step 4 , thread 9
19:10:21 step 5 , thread 10
19:10:21 step 6 , thread 10
19:10:21 step 7 , thread 10
Method AsyncCalls3() has a return value, which is a Task. The task that is started inside this method returns an integer. But doesn’t Task.Run() have to return Task<int> according to its definition? It is the await that changes the behavior. It returns the integer value (0). await has been implemented to shorten code, and this is what it does. The code is more legible.
Method AsyncCalls2() calls AsyncCalls3() and receives an integer and not a Task<int>. This is caused by the async keyword.
AsyncCalls2() itself returns void. This is the same issue as with AsyncCalls1(). However AsyncCalls3() can return a value to AsyncCalls2(), because AsyncCalls2() itself uses the async keyword in the method definition.
Check the program sequence. I marked the steps clearly to make comprehension easy. And then analyse the thread context switching. Between step 2 and 3 is a context switch operation, but not between 5, 6 and 7. This is the same behavior as in the first example code.
public static async void AsyncCalls4() {
Print(1); string s = await AsyncCalls5();
Print(4);
Console.ReadLine();
// return void
} //
// using System.Net.Http;
public static async Task<string> AsyncCalls5() {
using (HttpClient lClient = new HttpClient()) {
Print(2); string lResult = await lClient.GetStringAsync("http://www.microsoft.com");
Print(3); return lResult;
}
} //
example output:
19:11:47 step 1 , thread 10
19:11:47 step 2 , thread 10
19:11:48 step 3 , thread 14
19:11:48 step 4 , thread 14
When searching for async and await on the web you will find the emphasis on I/O. Most example programs concentrate on this and don’t explain what is roughly going on inside the async-I/O method itself. Basically .Net async-I/O methods deal with tasks and use a similar construction to Task.ContinueWith(). This is why I concentrated on different examples that can be used in any context (even though not very meaningful examples). The internet download example is more or less a classical one. You can use await on many I/O methods. Keep in mind that AsyncCalls4() returns void and that you are not supposed to call AsyncCalls5() from the Main() method, because you would have to add async to it.
C# Hardcore Programming 