C / C++ / MFC

12-Mar-08 17:34

Hi,

I'm about to rotate an image for display and I used RotateTransform() thanks to Mark Salsbery but now I'm having difficulty using it.

When I draw Image without RotateTransform,

g.DrawImage(&img,100,100,img.GetWidth(),img.GetHeight());

there's no problem. But when i added RotateTransform.

g.RotateTransform(330); // 30o elevation
g.DrawImage(&img,100,100,img.GetWidth(),img.GetHeight());

the image is displayed not in point (100,100) as expected rather in (137,37).

Is there something wrong in my code?
Do I have to add additional code for RotateTransform to work?
How will I display a rotated image in a fixed point?

Please help me.
Thanks.

Mark Salsbery12-Mar-08 18:26

Mark Salsbery

12-Mar-08 18:26

You could use Graphics::TranslateTransform() to shift the image vertically and/or horizontally.

Note that the order you set transforms with matrixes is important...
Here's some reference material: Transformations (GDI+)[^]

FWIW, Here's an example (I've posted here before) which rotates an image around its center point, like a propeller...

    Gdiplus::Bitmap SrcBitmap(L"C:\\test.tif", FALSE);
    
    Graphics DstGraphics(*this);

    REAL angle = 0.0f;
    for (int i = 0; i < 1440; ++i)
    {
        DstGraphics.ResetTransform();
        DstGraphics.RotateTransform(angle);
        DstGraphics.TranslateTransform(SrcBitmap.GetWidth() / 2.0f, SrcBitmap.GetHeight() / 2.0f, MatrixOrderAppend);
        DstGraphics.DrawImage(&SrcBitmap, -((INT)SrcBitmap.GetWidth() / 2), -((INT)SrcBitmap.GetHeight() / 2), SrcBitmap.GetWidth(), SrcBitmap.GetHeight());

        angle += 0.5f;

        // Use this to slow it down :)
//        ::Sleep(10);
    }

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

TooShy2Talk12-Mar-08 19:08

12-Mar-08 19:08

Thanks a lot.
Now I will try it.

TooShy2Talk12-Mar-08 19:53

12-Mar-08 19:53

Is there a way where I can position the image at the
upper left corner of the image to any point?

Like for example position the image corner at point (100,100).

(100,100)
....._____
..../ / / /
.../ / / /
..------

Rajkumar R12-Mar-08 21:05

Rajkumar R

12-Mar-08 21:05

TooShy2Talk wrote:
Like for example position the image corner at point (100,100).

Matrix matrix;
matrix.Translate(100.0f, 100.0f);
matrix.RotateAt(30.0f /*angle to rotate*/, PointF(100.0f, 100.0f), MatrixOrderAppend);
graphics.SetTransform(&matrix);
graphics.DrawImage(&img, PointF(0, 0));
graphics.ResetTransform();

TooShy2Talk12-Mar-08 22:26

12-Mar-08 22:26

Thank you for the reply.
I will try this.

Mark Salsbery13-Mar-08 6:34

Mark Salsbery

13-Mar-08 6:34

It's up to you to decide what the upper left corner of a rotated rectangular image is
and how you want it drawn.

You'll have to do a little math, but you have the functions to rotate and position.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Thread Response Time

jonsey2984712-Mar-08 17:15

12-Mar-08 17:15

I am writing an application to communicate with a controller, the data packet size is 7 bytes maximum 14 bytes both ways. I am trying to calculate my worst case frequency and I am using the following approximation, I seem to reall that baud rate is the approximate bit rate.

Max Controller Baud Rate = 500K
Max packet size = 56 bits.

500000/96 = 5.2 KHz

So based on this, and discounting controller and protocol converter latencies, I need to read the serial port every 2 microseconds.

Am I dreaming, or can a small thread handle it? How can I determine what size buffer I need to avoid overflow or loss of data?

Thanks once again for your replies.

krmed13-Mar-08 1:59

krmed

13-Mar-08 1:59

If you are truly talking about serial port usage, the data may be sent by your controller at 500K, but remember that for serial communications, every byte contains eight bits of data, plus (normally) one start bit and one stop bit.

Most serial ports cannot handle more than 115,200 baud (although perhaps some USB-Serial adapters can do better). Additionally, most serial ports provide a buffer that can hold more than one character - typically up to 16 - before you need to read the data.

Given that, at 500000 bps, with 10 bits/character gives 50000 Bytes per second. If you allow the port to buffer the data (let's say 16 characters), then you have 3125 full buffers per second which means a read every 320 microseconds.

The other question is how often does your controller actually send that data. It would appear you may need to send a 7-byte packet to the controller and then you get a 7-byte response from it. If that's the case, you obviously cannot get a response as often as you are calculating - in fact it would be about every 640 microseconds.

If you only query your controller periodically, then you won't get a response until you query, so you're in control of how often you must read the serial port.

Hope that helps.

Karl - WK5M
PP-ASEL-IA (N43CS)
PGP Key: 0xDB02E193
PGP Key Fingerprint: 8F06 5A2E 2735 892B 821C 871A 0411 94EA DB02 E193

jonsey2984713-Mar-08 12:20

13-Mar-08 12:20

Very helpful thanks.

David Crow13-Mar-08 2:24

David Crow

13-Mar-08 2:24

jonsey29847 wrote:
...I need to read the serial port every 2 microseconds.

Are you using a RTOS?

"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

jonsey2984713-Mar-08 12:30

13-Mar-08 12:30

Yes, however the controller(s) may not send responses back right away as some messages they handle may have a higher priority then my request for data. I am just trying to get a feel for the timing constraints for worst case data aquisition. Based on krmeds replay it would appear I am well within the capabilities of Windows.

Thanks

David Crow14-Mar-08 2:39

David Crow

14-Mar-08 2:39

jonsey29847 wrote:
Yes...Windows.

So which is it? Windows is not a RTOS, thus it cannot do anything every two microseconds.

Rather than polling, why don't you let the serial port tell you when it has data?

jonsey2984718-Mar-08 4:30

18-Mar-08 4:30

My application is to communicate with an ECU (OBDII controller), the ECU is real time.

The controller has to be polled to get the data, my attachment point is a network (CAN) thus any data I see may be for other devices on the network.

opaque pointer

George_George12-Mar-08 16:36

George_George

12-Mar-08 16:36

Hello everyone,

Opaque pointer must be a pointer points to inner (hidden to outside) struct or class?

(refer to the C++ part)

http://en.wikipedia.org/wiki/Opaque_pointer

thanks in advance,
George

Maxwell Chen12-Mar-08 18:30

Maxwell Chen

12-Mar-08 18:30

Interesting technique!

Maxwell Chen

George_George12-Mar-08 18:35

George_George

12-Mar-08 18:35

Thanks Maxwell,

Any answers to my original question? Smile | :)

regards,
George

Maxwell Chen12-Mar-08 18:42

Maxwell Chen

12-Mar-08 18:42

You have seen the C++ sample code on Wikipedia page.

As we know that if you declare an object member (as sample below):

class Object
{
  // ...
};
class User
{
  Object obj;
};

If you change anything to class Object's definition, the compiler recompiles class User (regarding to compilation unit), too.
But if you change into the below, it won't need to recompile class User.

class User
{
  class Object;
  Object* pObj;
};
class User::Object
{
  // ...
};

Maxwell Chen