BGRABitmap LineOrder.

[RWC]

I need to write to each consecutive pixel of a BGRABitmap starting from the bottom left corner to the top right. (using p^.red, p^.green, p^.blue, p^.alpha). This seemed straightforward, so before setting my PBGRAPixel pointer to image.data, I set image.LineOrder := riloBottomToTop; but got the Error: No member is provided to access property.

The link http://wiki.freepascal.org/BGRABitmap shows a Direct access to pixels example followed by the comment: Notice that the line order can be reverse, depending on the LineOrder property.

The example code shows ‘for n := bmp.NbPixels-1 downto 0 do’ but it does not change the ‘lineorder’ property, it only reverses the order of the pixel counter. i.e. if I change the code to: ‘for n := 0 to bmp.NbPixels-1 do’, I get an identical result. (which is not surprising since the pointer ‘p’ knows nothing about the counter ‘n’).

I didn’t want to use a separate scanline loop because my data is read consecutively from a MemoryStream (i.e. the input file is an XY matrix of 16bit big endian height values starting from bottom left to top right which I convert to pixel bytes).

At the moment my resulting image with the default LineOrder is upside down which I can easily flip in LazPaint but I was hoping there was a more direct way. (and without using the TrawImage method I remember from some time back). Any help is much appreciated – RWC.

[lainz]

You can also flip it with BGRABitmap and no need of LazPaint.

Code: Pascal  [Select][+][-]

1. Bitmap.VerticalFlip;

The LineOrder is read only. So this means that the order of the file in memory can be reversed, and you can see that accessing that property, but nothing more.

[RWC]

@Lainz: Yourself & circular are superstars in my books & Lazarus is the best blockbuster movie – many thanks – RWC.

[circular]

Indeed, the line order depend on the platform.

So if you write data from bottom to top, you can do as Lainz suggested depending on the value of LineOrder:

Code: [Select]

if Bitmap.LineOrder = riloTopToBottom then Bitmap.VerticalFlip;
Regards

[RWC]

if Bitmap.LineOrder = riloTopToBottom then Bitmap.VerticalFlip;

@circular: That’s a neat solution – now I understand why it’s read only. VerticalFlip worked well but I’ll add this to remind me its platform dependent – thank you & best regards.