How the code works

Question

Hi

In the below code how the below 2 line works

BitBlt Picture2.hDC, 0&, 0&, lNewWidth, lNewHeight, Picture1.hDC, lSourceX, lSourceY, SRCCOPY

Picture2.PaintPicture Picture1.Picture, 0, 0, lNewWidth, lNewHeight, lSourceX, lSourceY

    lOldWidth = Picture1.ScaleWidth \ Screen.TwipsPerPixelX
    lOldHeight = Picture1.ScaleHeight \ Screen.TwipsPerPixelY
    ' -=[ Calculate 70% of Width and Height ]=-
    lNewWidth = lOldWidth * 0.7
    lNewHeight = lOldHeight * 0.7
    ' -=[ Calculate Top Left of centered image ]=-
    lSourceX = (lOldWidth - lNewWidth) \ 2
    lSourceY = (lOldHeight - lNewHeight) \ 2

  ' -=[ Resize Destination Picture ]=-
    Picture2.Width = Picture2.Width - Picture2.ScaleWidth + (lNewWidth * Screen.TwipsPerPixelX)
    Picture2.Height = Picture2.Height - Picture2.ScaleHeight + (lNewHeight * Screen.TwipsPerPixelY)

  ' -=[ Crop Image ]=-
    BitBlt Picture2.hDC, 0&, 0&, lNewWidth, lNewHeight, Picture1.hDC, lSourceX, lSourceY, SRCCOPY

    Picture2.PaintPicture Picture1.Picture, 0, 0, lNewWidth, lNewHeight, lSourceX, lSourceY

Thanks

Muhammad Imran Ansari · Answer

Hello Ramco, The BitBlt function quickly copies a cropped portion of Picture1 (starting at lSourceX, lSourceY with dimensions lNewWidth, lNewHeight ) and pastes it onto Picture2 at (0,0) using direct pixel transfer. In contrast, PaintPicture redraws Picture1.Picture onto Picture2 , allowing resizing and scaling while maintaining image quality. BitBlt is faster for raw pixel copying, while PaintPicture provides more flexibility for transformations like stretching and resizing. Thanks!

Sophia Carter · Answer

Hello! I'd be happy to explain how the two lines of code you mentioned work: 1. BitBlt Function: - The `BitBlt` function stands for "Bit Block Transfer" and is commonly used in image processing for copying a rectangular block of pixels from a data source to a destination. - In your code snippet, this function is used to copy a portion of an image from `Picture1` to `Picture2`. - Here's a breakdown of the parameters: - `Picture2.hDC`: This is the destination device context (hDC) handle where the copied image will be placed. - `0, 0`: These coordinates represent the top-left corner of the destination where the copied image will be drawn. - `lNewWidth, lNewHeight`: These dimensions specify the width and height of the copied image in the destination. - `Picture1.hDC`: This is the source device context (hDC) handle from which the image will be copied. - `lSourceX, lSourceY`: These coordinates indicate the top-left corner of the portion of the source image to be copied. - `SRCCOPY`: This flag specifies the raster-operation code that defines how the source pixels are combined with the destination pixels. 2. Picture2.PaintPicture Method: - The `PaintPicture` method is part of Visual Basic for Applications (VBA) and is used to paint a picture onto a form or control. - In your code, this method is used to paint a portion of the picture from `Picture1` onto `Picture2`. - The parameters passed to this method specify the source picture, the destination coordinates, and the dimensions of the portion to be painted. These two lines of code work together to resize `Picture2`, determine the region of interest in `Picture1`, and then copy and paint the specified portion of the image onto `Picture2`. The `BitBlt` function is responsible for the low-level copying of pixels, while `PaintPicture` handles the higher-level painting onto the destination. I hope this explanation clarifies how these operations work in the context of your code. If you have any more questions or need further details, feel free to ask!

How the code works

Answers (2)