Moving a Bitmap inside PictureBox

Question

i have a problem with a Bitmap in C++/CLI. In short, i have to load a Bitmap chunk to a PictureBox, display it and move it few lines below. The steps i do are these:

1 - Load the full bitmap from the hard drive, and get it's parameters (width, heigth etc.).

2 - Create a PictureBox that be able to contain this Bitmap completely.

3 - Create a Bitmap, that i will use as draw area, and put it inside the PictureBox.

4 - Copy a chunk (first 150 lines) of the initial Bitmap to my draw area and display it.

5 - Move this chunk few lines below. (Here my problem).

When I move the image, i have an error: the image appears moved to left, and the right is the left part of the image. I uploaded images:

This is the image chunk before move it, all ok. http://i58.tinypic.com/2duf48x.png

This is the image after be moved, as you see, it appears moved to left. http://i61.tinypic.com/jz9ond.png

The method i use to "move" the image is:

1 - LockBits and obtain anIntPtr, which I convert to unsigned char*. 2 - Use memcpy (or memmove) to move the chunk.

Here the code, these are a class constructor (Windows Form constructor) and the method i use to display the chunk and move it:

MyForm(){
    InitializeComponent();
    //Get a test srcIm and it's parameters.
    srcIm = gcnew Bitmap("./img/zhbackground.bmp");
    iWidth = srcIm->Width;
    iHeigth = srcIm->Height;
    pxF = srcIm->PixelFormat;
    Bpp = Image::GetPixelFormatSize(pxF) / 8;

    //Prepare a PictureBox, which will be given as parameter to Windows Form.
    pb = gcnew PictureBox();
    pb->SizeMode = PictureBoxSizeMode::StretchImage;
    pb->Size = Drawing::Size(iWidth, iHeigth);
    pb->Location = Drawing::Point(0, 0);

    //Create draw area and put it into the PictureBox.
    drawArea = gcnew Bitmap(pb->Width, pb->Height, pxF);
    pb->Image = drawArea;

    this->Controls->Add(this->pb);
}

void test(){
    //This is the number of lines of my image chunk.
    int nLines = 150;

    //First, load the first 150 lines of my image (that's on hard drive).
    BitmapData ^srcData = srcIm->LockBits(
        Drawing::Rectangle(0, 0, iWidth, iHeigth),
        ImageLockMode::ReadOnly,
        pxF
    );
    unsigned char *srcStream = (unsigned char*)srcData->Scan0.ToPointer();

    //Prepare the draw area for paint my image chunk.
    BitmapData ^dstData = drawArea->LockBits(
        Drawing::Rectangle(0, 0, iWidth, iHeigth),
        ImageLockMode::ReadWrite,
        pxF
    );
    unsigned char *dAhandler = (unsigned char*)dstData->Scan0.ToPointer();

    //Paint the chunk. (My image's 150 first lines)
    memcpy(dAhandler, srcStream, iWidth * Bpp * nLines);

    //Unlock and refresh to see the image.
    drawArea->UnlockBits(dstData);
    this->pb->Refresh();

    //Wait 1 second...
    Threading::Thread::Sleep(1000);

    //Unlock draw area to move the image.
    dstData = drawArea->LockBits(
        Drawing::Rectangle(0, 0, iWidth, iHeigth),
        ImageLockMode::ReadWrite,
        pxF
    );
    dAhandler = (unsigned char*)dstData->Scan0.ToPointer();

    //First, move the image from the beggining to 150 lines below.
    memcpy(&dAhandler[nLines * iWidth * Bpp], dAhandler, iWidth * nLines * Bpp);

    //Paint the "hole" with black.
    memset(dAhandler, 0, iWidth * Bpp * nLines);

    //Unlock and display the image.
    drawArea->UnlockBits(dstData);
    this->pb->Refresh();

    //Unlock the source image (image load from hard drive).
    srcIm->UnlockBits(srcData);
 }

I have tested many ways:

1 - I have read that if you use LockBits(), the IntPtr you can obtain is the byte array of the pixels, one followed by another. This means that i can't have problems with issues like Bitmap organization in memory etc..

2 - I have tested memcpy and memmove.

3 - I have tested to do a simple for loop.

Nothing works, I don't know what to do.

Thanks, regards.

Answer 1

I have found a way to do this, I post it in C# (for C++/CLI is practically identical) I don't know if it's the better solution but it works.

/**
 * Number of lines that will be displaced down. This match with the
 * Height that the Bitmap returned by {@code getNextLines} must have.
 */
int displLines;

/**
 * Destination coordinates of the image chunk that will be 'moved'
 */
Point[] displaceCoords;

/**
 * Source image chunk that will me 'moved'
 */
Rectangle displaceArea;

/**
 * Destination coordinates for the new lines.
 */
Point[] newLineCoords;

/**
 * Dimensions of the rectangle formed by the new lines.
 */
Rectangle newLineArea;

/**
 * Auxiliar buffers for paint the displaced image and the new lines.
 */
Bitmap canvas1, canvas2;

/**
 * Graphics for each buffer (canvas1 and canvas2).
 */
Graphics canvas1Graphics, canvas2Grapchics;

/**
 * Flag indicating which buffer have to be used in a determined time.
 */
bool useCanvas1Graphics;

/**
 * Timer used to refresh the image.
 */
Timer timer;

/**
 * Retrieves the next lines to be painted at the top of
 * the image.
 */
abstract Bitmap getNextLines();

/**
 * Initializes the parameters which will be used to displace
 * the current bitmap in the PictureBox 'displLines' down.
 * 
 */
void InitDisplacingParameters() {
    displaceArea = new Rectangle(0, 0, Width, Height - displLines);
    displaceCoords = new Point[3];
    displaceCoords[0].X = 0;
    displaceCoords[0].Y = displLines;

    displaceCoords[1].X = Width;
    displaceCoords[1].Y = displLines;

    displaceCoords[2].X = 0;
    displaceCoords[2].Y = Height;
}

/**
 * Initializes the parameters use to insert the new lines
 * in the image.
 */
void InitNewLinesParameters() {
    newLineCoords = new Point[3];
    newLineCoords[0].X = 0;
    newLineCoords[0].Y = 0;

    newLineCoords[1].X = Width;
    newLineCoords[1].Y = 0;

    newLineCoords[2].X = 0;
    newLineCoords[2].Y = displLines;   

    newLineArea = new Rectangle(0, 0, Width, displLines);
}

/**
 * WARNING: in .NET framework version 3.0 or less, there is no possible
 * to use Grapchis.DrawImage for paint in the same image that have been used to obtain
 * the Graphics object.
 * 
 * Example, this is not possible:
 * {@code
 *      Graphics g = Graphics.fromImage(image);
 *      f.DrawImage(image, ....);
 *      // ERROR! "Grpahics" can not paint in the same image which has been generated him (Graphics).
 * }
 */
void DisplaceAndPaint(Object sender, EventArgs e) {
    try {
        // Stop paint.
        SuspendLayout();

        // Obtain the proper graphics object.
        Graphics g = useCanvas1Graphics ? canvas1Graphics : canvas2Grapchics;

        // Displace the current image 'desplLines' down.
        g.DrawImage(Image, displaceCoords, displaceArea, GraphicsUnit.Pixel);

        // Get the new lines.
        Bitmap bmp = getNextLines();

        // Draw the new lines in the top of the image.
        g.DrawImage(bmp, newLineCoords, newLineArea, GraphicsUnit.Pixel);

        // Set the just painted image as the display Image.
        Image = useCanvas1Graphics ? canvas1 : canvas2;

        // Next time, the other canvas and graphics will be used.
        useCanvas1Graphics = !useCanvas1Graphics;

        // Paint all.
        ResumeLayout();

        //NOTE: I don't know what is a better idea, do Suspend/Resume layout or 
        // Refresh() at the end.
    } catch(Exception) {
        if (IsRunning)
            Stop();
        MessageBox.Show("Error in LiveView");
    }
}