Develop Reference

GDI+ DrawImage notably slower in C++ (Win32) than in C# (WinForms)

I am porting an application from C# (WinForms) to C++ and noticed that drawing an image using GDI+ is much slower in C++, even though it uses the same API.
The image is loaded at application startup into a System.Drawing.Image or Gdiplus::Image, respectively.
The C# drawing code is (directly in the main form):
public Form1()
{
this.SetStyle(ControlStyles.UserPaint | ControlStyles.AllPaintingInWmPaint | ControlStyles.OptimizedDoubleBuffer, true);
this.image = Image.FromFile(...);
}
private readonly Image image;
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
var sw = Stopwatch.StartNew();
e.Graphics.TranslateTransform(this.translation.X, this.translation.Y); /* NOTE0 */
e.Graphics.DrawImage(this.image, 0, 0, this.image.Width, this.image.Height);
Debug.WriteLine(sw.Elapsed.TotalMilliseconds.ToString()); // ~3ms
}
Regarding SetStyle: AFAIK, these flags (1) make WndProc ignore WM_ERASEBKGND, and (2) allocate a temporary HDC and Graphics for double buffered drawing.
The C++ drawing code is more bloated.
I have browsed the reference source of System.Windows.Forms.Control to see how it handles HDC and how it implements double buffering.
As far as I can tell, my implementation matches that closely (see NOTE1) (note that I implemented it in C++ first and then looked at how it's in the .NET source -- I may have overlooked things).
The rest of the program is more or less what you get when you create a fresh Win32 project in VS2019. All error handling omitted for readability.
// In wWinMain:
Gdiplus::GdiplusStartupInput gdiplusStartupInput;
Gdiplus::GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
gdip_bitmap = Gdiplus::Image::FromFile(...);
// In the WndProc callback:
case WM_PAINT:
// Need this for the back buffer bitmap
RECT client_rect;
GetClientRect(hWnd, &client_rect);
int client_width = client_rect.right - client_rect.left;
int client_height = client_rect.bottom - client_rect.top;
// Double buffering
HDC hdc0 = BeginPaint(hWnd, &ps);
HDC hdc = CreateCompatibleDC(hdc0);
HBITMAP back_buffer = CreateCompatibleBitmap(hdc0, client_width, client_height); /* NOTE1 */
HBITMAP dummy_buffer = (HBITMAP)SelectObject(hdc, back_buffer);
// Create GDI+ stuff on top of HDC
Gdiplus::Graphics *graphics = Gdiplus::Graphics::FromHDC(hdc);
QueryPerformanceCounter(...);
graphics->DrawImage(gdip_bitmap, 0, 0, bitmap_width, bitmap_height);
/* print performance counter diff */ // -> ~27 ms typically
delete graphics;
// Double buffering
BitBlt(hdc0, 0, 0, client_width, client_height, hdc, 0, 0, SRCCOPY);
SelectObject(hdc, dummy_buffer);
DeleteObject(back_buffer);
DeleteDC(hdc); // This is the temporary double buffer HDC
EndPaint(hWnd, &ps);
/* NOTE1 */: In the .NET source code they don't use CreateCompatibleBitmap, but CreateDIBSection instead.
That improves performance from 27 ms to 21 ms and is very cumbersome (see below).
In both cases I am calling Control.Invalidate or InvalidateRect, respectively, when the mouse moves (OnMouseMove, WM_MOUSEMOVE). The goal is to implement panning with the mouse using SetTransform - that's irrelevant for now as long as draw performance is bad.
NOTE2: https://stackoverflow.com/a/1617930/653473
This answer suggests that using Gdiplus::CachedBitmap is the trick. However, I can find no evidence in the C# WinForms source code that it makes use of cached bitmaps in any way - the C# code uses GdipDrawImageRectI which maps to GdipDrawImageRectI, which maps to Graphics::DrawImage(IN Image* image, IN INT x, IN INT y, IN INT width, IN INT height).
Regarding /* NOTE1 */, here is the replacement for CreateCompatibleBitmap (just substitute CreateVeryCompatibleBitmap):
bool bFillBitmapInfo(HDC hdc, BITMAPINFO *pbmi)
{
HBITMAP hbm = NULL;
bool bRet = false;
// Create a dummy bitmap from which we can query color format info about the device surface.
hbm = CreateCompatibleBitmap(hdc, 1, 1);
pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
// Call first time to fill in BITMAPINFO header.
GetDIBits(hdc, hbm, 0, 0, NULL, pbmi, DIB_RGB_COLORS);
if ( pbmi->bmiHeader.biBitCount <= 8 ) {
// UNSUPPORTED
} else {
if ( pbmi->bmiHeader.biCompression == BI_BITFIELDS ) {
// Call a second time to get the color masks.
// It's a GetDIBits Win32 "feature".
GetDIBits(hdc, hbm, 0, pbmi->bmiHeader.biHeight, NULL, pbmi, DIB_RGB_COLORS);
}
bRet = true;
}
if (hbm != NULL) {
DeleteObject(hbm);
hbm = NULL;
}
return bRet;
}
HBITMAP CreateVeryCompatibleBitmap(HDC hdc, int width, int height)
{
BITMAPINFO *pbmi = (BITMAPINFO *)LocalAlloc(LMEM_ZEROINIT, 4096); // Because otherwise I would have to figure out the actual size of the color table at the end; whatever...
bFillBitmapInfo(hdc, pbmi);
pbmi->bmiHeader.biWidth = width;
pbmi->bmiHeader.biHeight = height;
if (pbmi->bmiHeader.biCompression == BI_RGB) {
pbmi->bmiHeader.biSizeImage = 0;
} else {
if ( pbmi->bmiHeader.biBitCount == 16 )
pbmi->bmiHeader.biSizeImage = width * height * 2;
else if ( pbmi->bmiHeader.biBitCount == 32 )
pbmi->bmiHeader.biSizeImage = width * height * 4;
else
pbmi->bmiHeader.biSizeImage = 0;
}
pbmi->bmiHeader.biClrUsed = 0;
pbmi->bmiHeader.biClrImportant = 0;
void *dummy;
HBITMAP back_buffer = CreateDIBSection(hdc, pbmi, DIB_RGB_COLORS, &dummy, NULL, 0);
LocalFree(pbmi);
return back_buffer;
}
Using a very compatible bitmap as the back buffer improves performance from 27 ms to 21 ms.
Regarding /* NOTE0 */ in the C# code -- the code is only fast if the transformation matrix doesn't scale. C# performance drops slightly when upscaling (~9ms), and drops significantly (~22ms) when downsampling.
This hints to: DrawImage probably wants to BitBlt if possible. But it can't in my C++ case because the Bitmap format (that was loaded from disk) is different from the back buffer format or something.
If I create a new more compatible bitmap (this time no clear difference between CreateCompatibleBitmap and CreateVeryCompatibleBitmap), and then draw the original bitmap onto that, and then only use the more compatible bitmap in the DrawImage call, then performance increases to about 4.5 ms. It also has the same performance characteristics when scaling now as the C# code.
if (better_bitmap == NULL)
{
HBITMAP tmp_bitmap = CreateVeryCompatibleBitmap(hdc0, gdip_bitmap->GetWidth(), gdip_bitmap->GetHeight());
HDC copy_hdc = CreateCompatibleDC(hdc0);
HGDIOBJ old = SelectObject(copy_hdc, tmp_bitmap);
Gdiplus::Graphics *copy_graphics = Gdiplus::Graphics::FromHDC(copy_hdc);
copy_graphics->DrawImage(gdip_bitmap, 0, 0, gdip_bitmap->GetWidth(), gdip_bitmap->GetHeight());
// Now tmp_bitmap contains the image, hopefully in the device's preferred format
delete copy_graphics;
SelectObject(copy_hdc, old);
DeleteDC(copy_hdc);
better_bitmap = Gdiplus::Bitmap::FromHBITMAP(tmp_bitmap, NULL);
}
BUT it's still consistently slower, there must be something missing still. And it raises a new question: Why is this not necessary in C# (same image and same machine)? Image.FromFile does not convert the bitmap format on loading as far as I can tell.
Why is the DrawImage call in the C++ code still slower, and what do I need to do to make it as fast as in C#?

I ended up replicating more of the .NET code insanity.
The magic call that makes it go fast is GdipImageForceValidation in System.Drawing.Image.FromFile. This function is basically not documented at all, and it is not even [officially] callable from C++. It is merely mentioned here: https://learn.microsoft.com/en-us/windows/win32/gdiplus/-gdiplus-image-flat
Gdiplus::Image::FromFile and GdipLoadImageFromFile don't actually load the full image into memory. It effectively gets copied from the disk every time it is being drawn. GdipImageForceValidation forces the image to be loaded into memory, or so it seems...
My initial idea of copying the image into a more compatible bitmap was on the right track, but the way I did it does not yield the best performance for GDI+ (because I used a GDI bitmap from the original HDC). Loading the image directly into a new GDI+ bitmap, regardless of pixel format, yields the same performance characteristics as seen in the C# implementation:
better_bitmap = new Gdiplus::Bitmap(gdip_bitmap->GetWidth(), gdip_bitmap->GetHeight(), PixelFormat24bppRGB);
Gdiplus::Graphics *graphics = Gdiplus::Graphics::FromImage(better_bitmap);
graphics->DrawImage(gdip_bitmap, 0, 0, gdip_bitmap->GetWidth(), gdip_bitmap->GetHeight());
delete graphics;
Even better yet, using PixelFormat32bppPARGB further improves performance substantially - the premultiplied alpha pays off when the image is repeatedly drawn (regardless of whether the source image has an alpha channel).
It seems calling GdipImageForceValidation effectively does something similar internally, although I don't know what it really does. Because Microsoft made it as impossible as they could to call the GDI+ flat API from C++ user code, I just modified Gdiplus::Image in my Windows SDK headers to include an appropriate method. Copying the bitmap explicitly to PARGB seems cleaner to me (and yields better performance).
Of course, after one finds out which undocumented function to use, google would also give some additional information: https://photosauce.net/blog/post/image-scaling-with-gdi-part-5-push-vs-pull-and-image-validation
GDI+ is not my favorite API.

How to add method in unmanaged code in a FaceRecognition project

I'm implementing a little FaceRecognition program using Emgu as a wrapper of OpenCV libraries. It seems to work fine, but I need a function that returns all the distances between the image sample and the faces in the database (the FaceRecognizer.Predict method implemented only returns the smallest distance and label).
So I built Emgu from Git, in order to adapt functions in the unmanaged code (cvextern.dll) to my needs.
Here's the original in face_c.cpp
void cveFaceRecognizerPredict(cv::face::FaceRecognizer* recognizer, cv::_InputArray* image, int* label, double* dist)
{
int l = -1;
double d = -1;
recognizer->predict(*image, l, d);
*label = l;
*dist = d;
}
that stores minimum distance and corresponding label in l and d, thanks to predict.
The method I wrote, following the summary in opencv face.hpp:
void cveFaceRecognizerPredictCollector(cv::face::FaceRecognizer * recognizer, cv::_InputArray * image, std::vector<int>* labels, std::vector<double>* distances)
{
std::map<int, double> result_map = std::map<int, double>();
cv::Ptr<cv::face::StandardCollector> collector = cv::face::StandardCollector::create();
recognizer->predict(*image, collector);
result_map = collector->getResultsMap();
for (std::map<int, double>::iterator it = result_map.begin(); it != result_map.end(); ++it) {
distances->push_back(it->second);
labels->push_back(it->first);
}
}
And the caller in c#
using (Emgu.CV.Util.VectorOfInt labels = new Emgu.CV.Util.VectorOfInt())
using (Emgu.CV.Util.VectorOfDouble distances = new Emgu.CV.Util.VectorOfDouble())
using (InputArray iaImage = image.GetInputArray())
{
FaceInvoke.cveFaceRecognizerPredictCollector(_ptr, iaImage, labels, distances);
}
[DllImport(CvInvoke.ExternLibrary, CallingConvention = CvInvoke.CvCallingConvention)]
internal extern static void cveFaceRecognizerPredictCollector(IntPtr recognizer, IntPtr image, IntPtr labels, IntPtr distances);
The application works in real-time, so the function in c# is called continuously. I have only two faces and one label (same person) stored in my database, so the first call returns correctly the only possible label and stores it in labels. Keeping the application running, returned labels and the size of labels vector keep growing, filled with unregistered labels that I don't know where he takes. It seems to me like the collector in c++ is not well referenced, so that every time the function is called it keeps storing data without releasing the previous ones, overwriting them. But it's only my guess, I'm not very good with c++.
What else could possily be wrong?
Hope you can help

c# screen transfer over socket efficient improve ways

thats how i wrote your beautiful code(some simple changes for me for easier understanding)
private void Form1_Load(object sender, EventArgs e)
{
prev = GetDesktopImage();//get a screenshot of the desktop;
cur = GetDesktopImage();//get a screenshot of the desktop;
var locked1 = cur.LockBits(new Rectangle(0, 0, cur.Width, cur.Height),
ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
var locked2 = prev.LockBits(new Rectangle(0, 0, prev.Width, prev.Height),
ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
ApplyXor(locked1, locked2);
compressionBuffer = new byte[1920* 1080 * 4];
// Compressed buffer -- where the data goes that we'll send.
int backbufSize = LZ4.LZ4Codec.MaximumOutputLength(this.compressionBuffer.Length) + 4;
backbuf = new CompressedCaptureScreen(backbufSize);
MessageBox.Show(compressionBuffer.Length.ToString());
int length = Compress();
MessageBox.Show(backbuf.Data.Length.ToString());//prints the new buffer size
}
the compression buffer length is for example 8294400
and the backbuff.Data.length is 8326947

I didn't like the compression suggestions, so here's what I would do.
You don't want to compress a video stream (so MPEG, AVI, etc are out of the question -- these don't have to be real-time) and you don't want to compress individual pictures (since that's just stupid).
Basically what you want to do is detect if things change and send the differences. You're on the right track with that; most video compressors do that. You also want a fast compression/decompression algorithm; especially if you go to more FPS that will become more relevant.
Differences. First off, eliminate all branches in your code, and make sure memory access is sequential (e.g. iterate x in the inner loop). The latter will give you cache locality. As for the differences, I'd probably use a 64-bit XOR; it's easy, branchless and fast.
If you want performance, it's probably better to do this in C++: The current C# implementation doesn't vectorize your code, and that will help you a great deal here.
Do something like this (I'm assuming 32bit pixel format):
for (int y=0; y<height; ++y) // change to PFor if you like
{
ulong* row1 = (ulong*)(image1BasePtr + image1Stride * y);
ulong* row2 = (ulong*)(image2BasePtr + image2Stride * y);
for (int x=0; x<width; x += 2)
row2[x] ^= row1[x];
}
Fast compression and decompression usually means simpler compression algorithms. https://code.google.com/p/lz4/ is such an algorithm, and there's a proper .NET port available for that as well. You might want to read on how it works too; there is a streaming feature in LZ4 and if you can make it handle 2 images instead of 1 that will probably give you a nice compression boost.
All in all, if you're trying to compress white noise, it simply won't work and your frame rate will drop. One way to solve this is to reduce the colors if you have too much 'randomness' in a frame. A measure for randomness is entropy, and there are several ways to get a measure of the entropy of a picture ( https://en.wikipedia.org/wiki/Entropy_(information_theory) ). I'd stick with a very simple one: check the size of the compressed picture -- if it's above a certain limit, reduce the number of bits; if below, increase the number of bits.
Note that increasing and decreasing bits is not done with shifting in this case; you don't need your bits to be removed, you simply need your compression to work better. It's probably just as good to use a simple 'AND' with a bitmask. For example, if you want to drop 2 bits, you can do it like this:
for (int y=0; y<height; ++y) // change to PFor if you like
{
ulong* row1 = (ulong*)(image1BasePtr + image1Stride * y);
ulong* row2 = (ulong*)(image2BasePtr + image2Stride * y);
ulong mask = 0xFFFCFCFCFFFCFCFC;
for (int x=0; x<width; x += 2)
row2[x] = (row2[x] ^ row1[x]) & mask;
}
PS: I'm not sure what I would do with the alpha component, I'll leave that up to your experimentation.
Good luck!
The long answer
I had some time to spare, so I just tested this approach. Here's some code to support it all.
This code normally run over 130 FPS with a nice constant memory pressure on my laptop, so the bottleneck shouldn't be here anymore. Note that you need LZ4 to get this working and that LZ4 is aimed at high speed, not high compression ratio's. A bit more on that later.
First we need something that we can use to hold all the data we're going to send. I'm not implementing the sockets stuff itself here (although that should be pretty simple using this as a start), I mainly focused on getting the data you need to send something over.
// The thing you send over a socket
public class CompressedCaptureScreen
{
public CompressedCaptureScreen(int size)
{
this.Data = new byte[size];
this.Size = 4;
}
public int Size;
public byte[] Data;
}
We also need a class that will hold all the magic:
public class CompressScreenCapture
{
Next, if I'm running high performance code, I make it a habit to preallocate all the buffers first. That'll save you time during the actual algorithmic stuff. 4 buffers of 1080p is about 33 MB, which is fine - so let's allocate that.
public CompressScreenCapture()
{
// Initialize with black screen; get bounds from screen.
this.screenBounds = Screen.PrimaryScreen.Bounds;
// Initialize 2 buffers - 1 for the current and 1 for the previous image
prev = new Bitmap(screenBounds.Width, screenBounds.Height, PixelFormat.Format32bppArgb);
cur = new Bitmap(screenBounds.Width, screenBounds.Height, PixelFormat.Format32bppArgb);
// Clear the 'prev' buffer - this is the initial state
using (Graphics g = Graphics.FromImage(prev))
{
g.Clear(Color.Black);
}
// Compression buffer -- we don't really need this but I'm lazy today.
compressionBuffer = new byte[screenBounds.Width * screenBounds.Height * 4];
// Compressed buffer -- where the data goes that we'll send.
int backbufSize = LZ4.LZ4Codec.MaximumOutputLength(this.compressionBuffer.Length) + 4;
backbuf = new CompressedCaptureScreen(backbufSize);
}
private Rectangle screenBounds;
private Bitmap prev;
private Bitmap cur;
private byte[] compressionBuffer;
private int backbufSize;
private CompressedCaptureScreen backbuf;
private int n = 0;
First thing to do is capture the screen. This is the easy part: simply fill the bitmap of the current screen:
private void Capture()
{
// Fill 'cur' with a screenshot
using (var gfxScreenshot = Graphics.FromImage(cur))
{
gfxScreenshot.CopyFromScreen(screenBounds.X, screenBounds.Y, 0, 0, screenBounds.Size, CopyPixelOperation.SourceCopy);
}
}
As I said, I don't want to compress 'raw' pixels. Instead, I'd much rather compress XOR masks of previous and the current image. Most of the times this will give you a whole lot of 0's, which is easy to compress:
private unsafe void ApplyXor(BitmapData previous, BitmapData current)
{
byte* prev0 = (byte*)previous.Scan0.ToPointer();
byte* cur0 = (byte*)current.Scan0.ToPointer();
int height = previous.Height;
int width = previous.Width;
int halfwidth = width / 2;
fixed (byte* target = this.compressionBuffer)
{
ulong* dst = (ulong*)target;
for (int y = 0; y < height; ++y)
{
ulong* prevRow = (ulong*)(prev0 + previous.Stride * y);
ulong* curRow = (ulong*)(cur0 + current.Stride * y);
for (int x = 0; x < halfwidth; ++x)
{
*(dst++) = curRow[x] ^ prevRow[x];
}
}
}
}
For the compression algorithm I simply pass the buffer to LZ4 and let it do its magic.
private int Compress()
{
// Grab the backbuf in an attempt to update it with new data
var backbuf = this.backbuf;
backbuf.Size = LZ4.LZ4Codec.Encode(
this.compressionBuffer, 0, this.compressionBuffer.Length,
backbuf.Data, 4, backbuf.Data.Length-4);
Buffer.BlockCopy(BitConverter.GetBytes(backbuf.Size), 0, backbuf.Data, 0, 4);
return backbuf.Size;
}
One thing to note here is that I make it a habit to put everything in my buffer that I need to send over the TCP/IP socket. I don't want to move data around if I can easily avoid it, so I'm simply putting everything that I need on the other side there.
As for the sockets itself, you can use a-sync TCP sockets here (I would), but if you do, you will need to add an extra buffer.
The only thing that remains is to glue everything together and put some statistics on the screen:
public void Iterate()
{
Stopwatch sw = Stopwatch.StartNew();
// Capture a screen:
Capture();
TimeSpan timeToCapture = sw.Elapsed;
// Lock both images:
var locked1 = cur.LockBits(new Rectangle(0, 0, cur.Width, cur.Height),
ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
var locked2 = prev.LockBits(new Rectangle(0, 0, prev.Width, prev.Height),
ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
try
{
// Xor screen:
ApplyXor(locked2, locked1);
TimeSpan timeToXor = sw.Elapsed;
// Compress screen:
int length = Compress();
TimeSpan timeToCompress = sw.Elapsed;
if ((++n) % 50 == 0)
{
Console.Write("Iteration: {0:0.00}s, {1:0.00}s, {2:0.00}s " +
"{3} Kb => {4:0.0} FPS \r",
timeToCapture.TotalSeconds, timeToXor.TotalSeconds,
timeToCompress.TotalSeconds, length / 1024,
1.0 / sw.Elapsed.TotalSeconds);
}
// Swap buffers:
var tmp = cur;
cur = prev;
prev = tmp;
}
finally
{
cur.UnlockBits(locked1);
prev.UnlockBits(locked2);
}
}
Note that I reduce Console output to ensure that's not the bottleneck. :-)
Simple improvements
It's a bit wasteful to compress all those 0's, right? It's pretty easy to track the min and max y position that has data using a simple boolean.
ulong tmp = curRow[x] ^ prevRow[x];
*(dst++) = tmp;
hasdata |= tmp != 0;
You also probably don't want to call Compress if you don't have to.
After adding this feature you'll get something like this on your screen:
Iteration: 0.00s, 0.01s, 0.01s 1 Kb => 152.0 FPS
Using another compression algorithm might also help. I stuck to LZ4 because it's simple to use, it's blazing fast and compresses pretty well -- still, there are other options that might work better. See http://fastcompression.blogspot.nl/ for a comparison.
If you have a bad connection or if you're streaming video over a remote connection, all this won't work. Best to reduce the pixel values here. That's quite simple: apply a simple 64-bit mask during the xor to both the previous and current picture... You can also try using indexed colors - anyhow, there's a ton of different things you can try here; I just kept it simple because that's probably good enough.
You can also use Parallel.For for the xor loop; personally I didn't really care about that.
A bit more challenging
If you have 1 server that is serving multiple clients, things will get a bit more challenging, as they will refresh at different rates. We want the fastest refreshing client to determine the server speed - not slowest. :-)
To implement this, the relation between the prev and cur has to change. If we simply 'xor' away like here, we'll end up with a completely garbled picture at the slower clients.
To solve that, we don't want to swap prev anymore, as it should hold key frames (that you'll refresh when the compressed data becomes too big) and cur will hold incremental data from the 'xor' results. This means you can basically grab an arbitrary 'xor'red frame and send it over the line - as long as the prev bitmap is recent.

H264 or Equaivalent Codec Streaming
There are various compressed streaming available which does almost everything that you can do to optimize screen sharing over network. There are many open source and commercial libraries to stream.
Screen transfer in Blocks
H264 already does this, but if you want to do it yourself, you have to divide your screens into smaller blocks of 100x100 pixels, and compare these blocks with previous version and send these blocks over network.
Window Render Information
Microsoft RDP does lot better, it does not send screen as a raster image, instead it analyzes screen and creates screen blocks based on the windows on the screen. It then analyzes contents of screen and sends image only if needed, if it is a text box with some text in it, RDP sends information to render text box with a text with font information and other information. So instead of sending image, it sends information on what to render.
You can combine all techniques and make a mixed protocol to send screen blocks with image and other rendering information.

Instead of handling data as an array of bytes, you can handle it as an array of integers.
int* p = (int*)((byte*)scan0.ToPointer() + y * stride);
int* p2 = (int*)((byte*)scan02.ToPointer() + y * stride2);
for (int x = 0; x < nWidth; x++)
{
//always get the complete pixel when differences are found
if (*p2 != 0)
*p = *p2
++p;
++p2;
}

Making a constantly updating Image (WPF)

So i am messing around with making a simple AI and stuff with basic C#, and in this project i have alot of points which i've been visualising by making a bitmap.
This bitmap i have rendered/loaded to an image object in the WPF window.. but my problem is that this is rendered each milisecond, making the framerate quite bad - so how would i make this better?
Can i load it 'constantly'? or should i take another approach?
What i got now is pretty simple but i can show the important parts anyway, taken out of the full class:
private static Bitmap BitMap = new Bitmap(500, 500);
static Graphics GraphicFromBitMap
{
get
{
return Graphics.FromImage(BitMap);
}
}
public static BitmapSource loadBitmapAsImage()
{
IntPtr intPtr = BitMap.GetHbitmap();
BitmapSource bitmapSource = null;
try
{
bitmapSource = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(intPtr,
IntPtr.Zero, Int32Rect.Empty,
System.Windows.Media.Imaging.BitmapSizeOptions.FromEmptyOptions());
}
finally
{
DeleteObject(intPtr);
}
DeleteObject(intPtr);
return bitmapSource;
}
This is ofcourse only the bitmap part - the actual loading is done the following way:
DispatcherTimer Timer = new DispatcherTimer();
public MainWindow()
{
this.Timer.Tick += new EventHandler(Timer_Tick);
this.Timer.Interval = new TimeSpan(0, 0, 0, 1);
this.Timer.Start();
}
void Timer_Tick(object sender, EventArgs e)
{
WorldMap.Draw();
map.Source = WorldMap.BitMapSource;
}
This is ofcourse only the important parts - i hope my question is understandable but just to clearify and repeat:
I need a WPF image to update 'every frame' or everytime specific values change.
My question might have been answered before, but i couldn't really find anything that work nor something suiting this instance.
BTW making the timer set off more frequently creates an error with the loading, but the exact error code, i can't remember, and i can't seem to create it again - never the less this probably isn't the most practical way of doing this.
EDIT:
For clarification, this is all i got right now: http://imgur.com/EIiSRFQ
I want nothing fancy - it's just for personal projects playing around with programming and math, and that's alot easier if i can visualize the objects that i am 'moving' in my 2D plane.
Right now i am playing around with physics and gravity, trying to create a simple solar system with working physics. this is all just side projects to get to know the different tools better when i am too tired to work on my main project.

I would look to represent the visual elements of the bitmap as controls in WPF. That way you can update them directly and as frequently as they change, without the overhead of creating a bitmap and rendering it.
Performance would be far greater as you'd only update the changes in value.
To demonstrate the point, create a control...
<UserControl x:Class="Sample_Chart.Views.CodeBehindChart"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>
<Canvas x:Name="LayoutRoot" />
</UserControl>
This is as simple as they get. Next edit the code behind file...
public partial class CodeBehindChart : UserControl
{
public CodeBehindChart()
{
InitializeComponent();
Respond();
}
private async void Respond()
{
await Task.Delay(2000);
Random r = new Random();
while (true)
{
this.LayoutRoot.Children.Clear();
for (int i = 0; i < 100; i++)
{
Rectangle rectangle = new Rectangle();
rectangle.SetValue(Canvas.LeftProperty, r.NextDouble() * this.LayoutRoot.ActualWidth);
rectangle.SetValue(Canvas.TopProperty, r.NextDouble() * this.LayoutRoot.ActualHeight);
rectangle.Width = 2;
rectangle.Height = 2;
rectangle.Fill = Brushes.Black;
this.LayoutRoot.Children.Add(rectangle);
}
await Task.Delay(500);
}
}
}
In this code behind we have an async void method which firstly waits for 2 seconds (optional) before then creating 100 visual elements at random locations within the control. It refreshes this every 1/2 second.
If you did the same thing, but based those locations, sizes and fill - even use different shapes - I think you'll have a high performing, scaling and easily extendable solution to your requirements.
Taking this the next stage and controlling from a ViewModel will require a bit more thought which for your 'first project' - albeit an interesting one, may be a step ambitious ;)

How to deal with memory stack overload

I am trying to programm an edge detection method. And I have used emgucv Image class. Since I need gray values I have declared it as
Image<Gray,float> MyImage = new Image<Gray,float>;
I select an image and assign its pixel values into MyImage as
public void selectImage()
{
OpenFileDialog opp = new OpenFileDialog();
if (opp.ShowDialog() == DialogResult.OK)
{
MyImage = new Image<Gray,float>(opp.FileName);
InputArray = new Image<Gray, float>(opp.FileName);
Convert.ToString(MyImage);
pictureBox1.Image = MyImage.ToBitmap();
}
}
When I click on edge detection button it calls the main recursive function
private void detect_edges_Click(object sender, EventArgs e)
{
hueckel_operator(1, 1);
}
This operator repeats itself with 5pixel intervals. In other words I apply it on x axis by incrementing x parameter by 5 and at the end of the row I increment y axis by 5 and so on.
In hueckel_operator, the function "a()" which calculates again a very heavy formula is being called 8 times. Here is the a() function
public double a(int j, int counter6, int counter7)
{
for (int II = 0; II <= j ; II++)
{
for (KK = 1; KK < 70; KK++)
{
x_value = input_i_x(KK); //this function brings the x coordinate
y_value = input_i_y(KK); // this function brings the y coordinate
result += HueckelDisk(x_value,y_value,j) * MyImage[x_value+counter6, y_value+counter7].Intensity;
//MyImage.Dispose();
}
}
return result;
}
But the problem is approximately at the coordinate (75,5) it throws a stack overflow exception. I debugged it with performance analyse and MyImage seems to eat all memory. You probably wants to see recursive function but since it is too big I can not put it here and I am sure that recursive function (hueckel_operator()) can not reach terminating condition since I found out how many times it has been called. What I want is to find out if there is another way to calculate "result" in a more efficient way.
My other question is that, object MyImage is used in function a() 69*j times and does it mean that it allocates memory space 69*j times whenever a() is called?
During my desperate tries, I have declared and defined almost every variable as global in order to reduce the memory usage because I have thought otherwise whenever hueckel_operator() and a() are called, local variables would allocate extra memory in stack over and over, is it a good or necessary approach?
I use 4 very nested and heavy functions and I don't use any class. Would it be the main problem? To be honest I don't see anything here to convert into class.
I know, I have asked too many questions but I am really desperate right now. I am reading articles since some weeks and I guess I need a kick start. Any help would be appreciated.

A stack overflow exception doesn't really have much to do with memory usage - it's from stack usage. In your case, a recursive call.
Recursion can only go so deep until the stack is exhausted. Once that happens, you get your stack overflow.
If you are not in an unbounded recursion but you need to go deeper, you can specify the stack size when you create a thread, and run your recursive function on that:
var stackSize = 10000000;
var thread = new Thread(new ThreadStart(StartDetection), stackSize);
However, the default size is 1MB - which is quite a bit for most tasks. You may want to verify your recursion is in fact not unbound, or that you can't reduce or remove it.