Graeme Geldenhuys wrote 19 lines
Hi,
I'm trying to implement fpimage support in the fpGUI widget framework.
I'm really confused at the moment. :) The following queries apply
to X11 (xlib) only. My GDI (windows) support will come later.
My current BMP image implementation (which doesn't use the fpimage
unit) has an internal TXImage. One for the Mask and one for the Image
Data.
Now creating a descendant of TFPCustomImage, I know I need to
implement the following two methods.
procedure SetInternalPixel(x, y: integer; Value: integer); override;
function GetInternalPixel(x, y: integer): integer; override;
1) Those are the only abstract methods. So where am I supposed to
create the instance of TXImage and assign it the internal data? When
am I supposed to assign the internal data?
See below.
2) Am I supposed to descend from TFPCustomImage or TFPMemoryImage?
What's the difference?
You must descend from TFPCustomImage.
The difference is that TFPCustomImage provides no storage for the actual image data: all methods rely on the SetInternalPixel and GetInternalPixel methods. Careful, these are palette based. There are 2 other virtual calls which retrieve/set the actual colors:
procedure SetInternalColor (x,y:integer; const Value:TFPColor); virtual;
function GetInternalColor (x,y:integer) : TFPColor; virtual;
By default, these work with the palette using the index retrieved/provided by SetInternalPixel and GetInternalPixel.
It may make more sense to you to reverse the situation, depending on your storage format.
TFPMemoryImage actually stores the data in an array in memory, independent of any device. (it stores the RGB values directly or using a palette)
You should create a TFPCustomImage descendent which handles the storage through the TXImage auxiliary object.
What you should do:
Create a descendent of TFPCustomImage, say TFPGUIImage. It has an internal TXImage field. When the dimensions are set of the image (in SetSize), you allocate the TXImage with the correct dimensions: So I think the best is to override setsize, and create the TXImage there. Override destroy to free The TXImage. Then you override SetInternalColor, GetInternalColor, and SetInternalPixel and GetInternalPixel so they work as expected: they'll probably simply access the TXImage instance methods, and convert the internal format of TXImage to TFPColors.
I hope this makes sense. If not, shoot :-)
Michael.
