Alpha Blending

unit BlendU;

interface

uses

Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,

StdCtrls, jpeg, ExtCtrls, Spin,math;

type

TForm1 = class(TForm)

Panel1: TPanel;

ImgMain: TImage;

ImgBackground: TImage;

ImgMaskMap: TImage;

Label1: TLabel;

Label2: TLabel;

Label3: TLabel;

SpinEdit1: TSpinEdit;

SpinEdit2: TSpinEdit;

Label4: TLabel;

Label5: TLabel;

procedure TileBackground;

procedure DrawBlend;

procedure FormCreate(Sender: TObject);

procedure FormResize(Sender: TObject);

procedure FormPaint(Sender: TObject);

procedure SpinEdit2Change(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;

var

Form1: TForm1;

BlendedBitmap: tbitmap;

implementation

{$R *.DFM}

procedure tform1.TileBackground;

var

x,y: integer;

// x,y -coordinates in height's and width's of the background

h,w: integer; // the width and height of the background image being tiled

begin

h:=imgBackground.height;

w:=imgBackground.Width;

for x:=0 to 5 do

for y:=0 to 5 do

BlendedBitmap.canvas.draw(x*w,y*h,imgBackground.picture.bitmap);

// draw the background in different locations

end;

procedure tform1.DrawBlend;

var

maskpba: pbytearray; // pointer to information in the mask bitmap

Blendpba: pbytearray; // pointer to information in blendedbitmap

Mainpba: pbytearray; // pointer to information in the main image being averaged with the background

mx,my: integer; // used to draw the blend in an area that won't try accessing information outside the images

x,y: integer; // coordinates of a pixel

x2: integer; // used to hold x shl 2

x3: integer; // used to hold x2 + left for the memory location in the

left,top: integer; // the left and top positions of the blended graphic

begin

TileBackGround; // clear blendedbitmap and tile the background image

Left:=SpinEdit1.Value;

top:=SpinEdit2.Value;

// get the input coordinates

mx:=Min(Min(BlendedBitmap.width-left,imgMaskMap.width),imgMain.width);

// get the smallest width of an image

my:=Min(Min(BlendedBitmap.Height-top,imgMaskMap.Height),imgMain.Height);

// get the smallest Height of an image

dec(mx); // subtract 1

dec(my); // subtract 1

left:=left shl 2; // now, instead of a # pixels from pixel 0, it is the number of bytes into the pointer

// it is better to do this here than in the loop

for y:=my downto 0 do // loop through the rows of pixels

begin

maskpba:=imgMaskMap.Picture.Bitmap.ScanLine[y];

Blendpba:=BlendedBitmap.ScanLine[y+top];

Mainpba:=imgMain.Picture.Bitmap.ScanLine[y];

// get the pointers to rows of pixels data

for x:=mx downto 0 do // loop through the various pixels in a row

begin

x2:=x shl 2;

x3:=x2+left;

// calculate the number of bytes into the pointer to the memory location of the pixel

// average the 2 colours together by a ratio determined by the Mask

// each part of the colour(red, green, and blue) is averaged separately

Blendpba[x3]:=(Mainpba[x2]*Maskpba[x2]+Blendpba[x3]*($FF-Maskpba[x2])) shr 8;

// average blue bytes

inc(x2);

inc(x3);

Blendpba[x3]:=(Mainpba[x2]*Maskpba[x2]+Blendpba[x3]*($FF-Maskpba[x2])) shr 8;

// average green bytes

inc(x2);

inc(x3);

Blendpba[x2+left]:=(Mainpba[x2]*Maskpba[x2]+Blendpba[x3]*($FF-Maskpba[x2])) shr 8;

// average red bytes

end;

end;

canvas.draw(panel1.width,0,blendedBitmap);

// draw the bitmap on the form

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

BlendedBitmap:=tbitmap.create;

imgMain.picture.bitmap.pixelformat:=pf32bit;

imgMaskMap.picture.bitmap.pixelformat:=pf32bit;

end;

procedure TForm1.FormResize(Sender: TObject);

begin

BlendedBitmap.Height:=clientheight;

if panel1.width

BlendedBitmap.Width:=clientwidth-panel1.Width;

BlendedBitmap.pixelformat:=pf32bit;

DrawBlend;

Canvas.Draw(panel1.width,0,BlendedBitmap);

end;

procedure TForm1.FormPaint(Sender: TObject);

begin

Canvas.Draw(panel1.width,0,BlendedBitmap);

end;

procedure TForm1.SpinEdit2Change(Sender: TObject);

begin // also linked to spinedit1

drawblend;

end;

end.