[fpc-pascal] Questions regarding FPImage's TFPMemoryImage.FData variable

[Michael Van Canneyt]

On Thu, 26 May 2016, Graeme Geldenhuys wrote:

> On 2016-05-26 12:08, Michael Van Canneyt wrote:
>> BUT: 
>> depending on UsePalette, it contains indexes in the palette or RGB Data.
>
> Oh, I forgot about Palette usage. I’ll have to check for that in my
> code. Does setting UsePalette := False at runtime auto convert palette
> data to RGB data? I had a look at TFPCustomImage.SetUsePalette() but it
> is not immediately obvious what it does at runtime (after image data was
> already loaded).

Yes it does, but this is very slow.

>> It is definitely possible that you are wrong. 
>
> :-) Definitely not the first time that happened.
>
>
>
>> Yes. The Pixels array is a palette. The colors array is RGBA.
>
> Good to know the difference, thanks.
>
>
>>> 4) What is the order in which the colour channel information is stored
>>>   in memory? RGB, BGR, RGBA, BGRA, ARGB, ABGR etc?
>> 
>> You should not worry about this. The whole idea is that you do not use the
>> internal format, but just use the colors array:
>
> But that would be super slow.

Yes. But sometimes it is all you've got; e.g. when drawing on an image.

>
>>> The reason for all these questions. I've got a image loaded in a
>>> TFPMemoryImage instance. I need to pass the the raw pixel data buffer to
>>> a 3rd party library for further processing. But I need to tell that
>>> 3rd party library a bit about the data I'm giving it (colour channel
>>> size, colour channel order etc).
>> 
>> This is not supported for TFPMemoryImage.
>
> Well, I seem to have it almost working (see my other message with
> attached image). I didn’t know about the TFPCompactImgBase descendants -
> I’ll give them a try instead. That seems more like what I need.

It probably is.

For completeness, in fpImage: when doing 16 bit image, then
   (16-bit color value)=(8-bit color value) shl 8 + (8-bit color value)

Michael.