Mega Code Archive
Transparent Fill
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Title: Transparent Fill
Question: This example show how to make a transparent fill.
The routine is greatly inspired by a transparent fill eample by Yosmany Sez Concepcin but optimized by use of scanlines.
Answer:
ABitmap : The bitmap to draw the transparent fill on
ARect : The rectangle to fill
AColor : The color of the fill
AAlpha : Alphavalue (transparency)
0 = Full transparent, 100 = No transparency
Please note that the bitmap is converted to 24bit colors.
The alphavalues are calculated and stored in AlphaTable.
The table is then used to find the correct blend value for each color of the original image.
uses
graphics, windows, extctrls, classes, sysutils, controls;
const
PIXELCOUNTMAX = 32768;
type
pRGBArray = ^TRGBArray;
TRGBArray = array[0..PIXELCOUNTMAX] of TRGBTriple;
procedure FillTransparency( ABitmap : graphics.TBitmap;
ARect : TRect; AColor : TColor;
AAlpha : integer );
var
i,x,y : integer;
Scan : pRGBArray;
Alpha : real;
r,g,b : byte;
AlphaTable : array[1..2,0..255] of integer;
begin
ABitmap.PixelFormat := pf24bit;
r := fColor and $000000FF;
g := (fColor and $0000FF00) shr 8;
b := (fColor and $00FF0000) shr 16;
Alpha := AAlpha / 100;
for i := 0 to 255 do
begin
AlphaTable[1,i] := Trunc( i*Alpha );
AlphaTable[2,i] := Trunc( i*(1-Alpha) );
end;
for y := ARect.Top to ARect.Bottom do
begin
Scan := pRGBArray( ABitmap.ScanLine[y] );
for x := ARect.Left to ARect.Right do
begin
Scan[x].rgbtBlue := AlphaTable[1, b] + AlphaTable[2, Scan[x].rgbtBlue];
Scan[x].rgbtGreen := AlphaTable[1, g] + AlphaTable[2, Scan[x].rgbtGreen];
Scan[x].rgbtRed := AlphaTable[1, r] + AlphaTable[2, Scan[x].rgbtRed];
end;
end;
end;
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