Mega Code Archive
Graphictnt
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GRAPHICS
-best ways to set up components for drawing.
1. declare a bitmap in FormCreate and immediately
assign that to the Picture.Graphic property of
a TImage component placed on the main drawing
form. Note that here we also set the bitmap's
extents to be the same as the extents of the
form's image component:
procedure TFormLab3D.FormCreate(Sender: TObject);
var
Bitmap: TBitmap;
begin
Bitmap := TBitmap.Create;
Bitmap.Width := Image.Width;
Bitmap.Height := Image.Height;
Image.Picture.Graphic := Bitmap;
ShowFigure; //also interesting; see below
end;
note how next we declare a variable of type TPantograph
within the function, and then we call it's constructor
WITH A PARAMETER OF THE IMAGE CANVAS
PROCEDURE TFormLab3D.ShowFigure;
VAR
pantograph: TPantoGraph;
BEGIN
Image.Canvas.FillRect( Rect(0,0, Width, Height) );
pantograph := TPantoGraph.Create(Image.Canvas);
{Use whole canvas as viewport}
{although you can do more in terms of viewports
using the pantograph's viewport method [elsewhere]...}
pantograph.ViewPort(0.00,1.00, 0.00,1.00);
TRY
{do stuff...}
FINALLY
pantograph.free
END
END;
In the example program from which the code above is taken,
the pantograph object is declared in another unit, and
'A pantoGraph object maps "World Coordinates" to a Delphi
Canvas'. This to is interesting in that it brings to mind
what Ed Yourdon said once about how a non-trivial graphics
app coded with good object-orientation should haver three
main layers of objects:
1. a 'screen' layer
2. a 'functional code' layer, and
3. a 'data' layer
************************************************************
beware of rounding down in complex calculations, as this may
well result in significant alterations to x,y coordinates
for instance. So always do the calculations with floating
point type variables until the very last moment, converting
to Integer types a necessary.
************************************************************
Tip:
Use the initialization section to initaialise variables and/or
executer program startup code as the initialization section
'contains statements that are executed, in the order in which
they appear, on program start-up'.
************************************************************
EXCEPTIONS
declare your new user-defined exceptions as CLASSES in the
Interface/Type section at the top of a unit, like so
INTERFACE
TYPE
EVectorError = CLASS(Exception);
EMatrixError = CLASS(Exception);
and then (when appropriate conditions hold true) 'RAISE' the
exception as follows:
raise EMatrixError.Create('Matrix multiplication error')
************************************************************
alternatively (probably not as good) we can declare a bitmap
variable as an attribute of a draw object, creating it in the
object's constructor, and freeing it in the object's destructor:
Note also how we do operations on the bitmap (in
FillTBitMapDrawArea), copying the bitmap to the canvas passed
in at the end of the function
type
TCNSVDraw = class(TObject)
constructor Create;
destructor Destroy; override;
procedure FillTBitMapDrawArea(thisCanvas: TCanvas;
cWidth, cHeight: Integer);
{et cetera}
private
memBitMap: Graphics.TBitMap;
public
end;
var
CNSVDraw: TCNSVDraw;
implementation
constructor TCNSVDraw.Create;
begin
memBitMap := Graphics.TBitmap.Create;
memBitMap.Width := Screen.Width;
memBitMap.Height := Screen.Height;
end;
destructor TCNSVDraw.Destroy;
begin
memBitMap.Free;
end;
procedure TCNSVDraw.FillTBitMapDrawArea(thisCanvas: TCanvas;
cWidth, cHeight: Integer);
{set up the drawing area to be white not grey...}
var
imageRect: TRect;
begin
with memBitMap.Canvas do
begin
Brush.Color := clWhite;
imageRect.Left := 0;
imageRect.Top := 0;
//imageRect.Right := cWidth;
//imageRect.Bottom := cHeight;
imageRect.Right := Screen.Width;
imageRect.Bottom := Screen.Height;
FillRect(imageRect);
end;
thisCanvas.Draw(0, 0, memBitMap);
end;
***************************************************************
When sizing, say, a TImage to the form on which it sits, be careful
of using the WIDTH of the form as in MainForm.Width. The borders
of forms (ie the borders of windows) are user-configurable so the
width of the border of the form will vary unpredictably. But if
you use clientWidth and clientHeight instead this avoids the
problem, since clientWidth is formWidth minus border.
***************************************************************
**************************************
If you want to maintain a LARGE LIST OF IMAGES, then
consider using an Image List component.
From the Delphi Help:
The TImageList component is a collection of same-sized
images, each of which can be referred to by its index.
Unit
Controls
Description
Image lists are used to efficiently manage large sets of icons or bitmaps.
All images in an image list are contained in a single, wide bitmap in
screen device format. An image list may also include a monochrome bitmap
that contains masks used to draw images transparently (icon style).
The image list is capable of holding a large number of same sized images
and retrieving them via their index within the range 0 to n - 1. The image
list also has methods to facilitate storing, retrieving, and drawing of
the stored images.
The TImageList is derived from TCustomImageList and exposes many of the
protected properties and methods of the TCustomImageList.
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