Use TPictureClip custom component to extract portions of a matrix of
pictures and assign the "cell picture" to another picture control.
TPictureClip
What I have in mind, is to create a new Delphi
component that allows you to extract portions of a matrix of pictures
(images) and assign the "cell picture" to another image component, or to
another component that has the
Canvas property
to draw on.
The TPictureClip control will store multiple images that can be used by
other Delphi controls. All images are contained in a single bitmap.
Selected regions can then be 'clipped' from the bitmap and, for example,
used with a TImage control to create animations.
Note: The TPictureClip control is similar to the TImageList,
however, they differ in that all image resources in the TPictureClip
component must be contained in a single bitmap whereas the TImageList
control is a collection of separate bitmaps.
... New Control
Before we get to the code, if you are not familiar
with custom component building in Delphi, try reading the article
Custom
Component Development, we need some of the info in this article to
understand the methods we will use below.
For the start we have to derive our component from, naturally enough,
the TImage. Reason: we want a control that is prepared to take a
picture property. Again, if you are not sure how to derive a new component
from an existing one, read the following HowTo: How To
Create the Basic Unit for a New Component (these are the steps to
crating a new graphics component from TImage).
TPictureClip = class(TImage)
To accomplish our task, we can divide
the image contained in the TPictureClip picture property into a specified
number of rows and columns. The rows and columns create cells which can
then be accessed using an Index number. The cells are indexed beginning at
0 and increase from left to right and top to bottom using the GraphicCell
property, precisely from 0 to (Cols * Rows) - 1.
...
type
TPictureClip =
class(TImage)
private
FRows:Integer;
FCols:Integer;
FPicture:TPicture;
function GetCellGraphic
(Index:Integer):TPicture;
public
constructor
Create(AOwner: TComponent) ; override;
destructor Destroy; override;
property
GraphicCell[Index:Integer]:TPicture read
GetCellGraphic;
published
property
Rows:Integer read FRows write FRows;
property Cols:Integer read FCols write
FCols;
end;
...
Now, we have to create a
function GetCellGraphic which will extract a portion of a picture and
assign it to another picture property.
function
TPictureClip.GetCellGraphic(Index:Integer):TPicture;
var
BWidth, BHeight : Integer;
SrcRect, DestRect :
TRect;
begin
BWidth := Picture.Width div
FCols;
BHeight := Picture.Height div
FRows;
DestRect := Rect(0, 0, BWidth, BHeight)
;
SrcRect.Left := (Index mod Cols) *
BWidth;
SrcRect.Top := (Index div Cols) *
BHeight;
SrcRect.Right := SrcRect.Left + BWidth;
SrcRect.Bottom := SrcRect.Top + BHeight;
FPicture.Bitmap.Width := BWidth;
FPicture.Bitmap.Height :=
BHeight;
FPicture.Bitmap.Canvas.CopyRect(DestRect, Canvas,
SrcRect) ;
GetCellGraphic := FPicture;
end;
Download and use
You are now ready to
download the
PictureClip unit (with TPictureClip component) and the
demo project.
Installing into the Component palette
First, download the
TPictureClip component. The TPictureClip comes as a single unit file (.pas
extension). You'll need to add the component into an existing package.
Here's
How to
Install a Custom Component in Delphi (into Existing Package).
| 
