如何正确实现TBitmap的scanline访问? [英] How to implement the scanline access of TBitmap correctly?
问题描述
我正在尝试根据Embarcadero上的文章来访问位图的扫描线.使用
I am trying to access the scanline of a Bitmap according to an article on Embarcadero. Using scanlines like
for y := 0 to n do
begin
line := bitmap.scanline [y];
for x := 0 to n do line [x] := value;
我以前已经实现了.我注意到访问扫描线会花费相对较长的时间,上面提到的文章为此提供了一种解决方案.我无法正确实施.我的代码是:
I have implemented before. I noticed that accessing a scanline takes relatively much time and the article mentioned above offers a solution to that. I am not able to implement it correctly. My code is:
unit SCTester;
interface
uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
ExtCtrls;
type
TRGBQuad = packed record
b: uInt8;
g: uInt8;
r: uInt8;
alpha: uInt8;
end; // Record: TQuad //
// Override the definitions in Graphics.pas
TRGBQuadArray = packed array [0..MaxInt div SizeOf (TRGBQuad) - 1] of TRGBQuad;
PRGBQuadArray = ^TRGBQuadArray;
TForm1 = class(TForm)
Image: TImage;
procedure ImageDblClick(Sender: TObject);
end;
var Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.ImageDblClick(Sender: TObject);
var Bitmap: TBitmap;
q: TRGBQuad;
x, y: NativeInt;
FirstLine: PRGBQuadArray;
idx: NativeInt;
LineLength: NativeInt;
begin
q.r := 0; q.g := 0;
Bitmap := TBitmap.Create;
Bitmap.Height := Image.Height;
Bitmap.Width := Image.Width;
Bitmap.PixelFormat := pf32Bit;
FirstLine := Bitmap.ScanLine [0];
LineLength := (NativeInt (Bitmap.Scanline [1]) - NativeInt (FirstLine)) div SizeOf (TRGBQuad);
try
for y := Bitmap.Height - 1 downto 0 do
begin
for x := 0 to Bitmap.Width - 1 do
begin
q.b := (x xor y) mod 255;
idx := y * LineLength + x;
FirstLine [idx] := q;
end; // for
end; // for
Image.Picture.Assign (Bitmap);
finally
Bitmap.Free;
end; // try..finally
end;
end.
当y = 1和x = 0时,我总是会得到非法访问.LineLength为负数(位图的宽度),但这是可以预期的.我在做什么错了?
And I always get an illegal access when y=1 and x=0. LineLength is negative (the width of the bitmap), but that might be expected. What am I doing wrong?
上面的代码已更改,以反映到目前为止已处理的评论.
The code above is changed to reflect the remarks processed till so far.
推荐答案
要不访问任何负索引,我会这样做
To not to access any negative index, I would do
procedure TForm1.Button1Click(Sender: TObject);
var Bitmap: TBitmap;
q: TRGBQuad;
x, y: LongInt;
line{, FirstLine}: PRGBQuadArray;
idx: NativeInt;
LastLine: PRGBQuadArray;
LineLength: NativeInt;
begin
q.r := 0; q.g := 0;
Bitmap := TBitmap.Create;
Bitmap.Height := Image.Height;
Bitmap.Width := Image.Width;
Bitmap.PixelFormat := pf32Bit;
LastLine := Bitmap.ScanLine[Bitmap.Height - 1];
LineLength := (NativeInt(Bitmap.Scanline[Bitmap.Height - 2]) - NativeInt(Lastline)) div SizeOf(TRGBQuad);
try
for y := 0 to Bitmap.Height - 1 do
begin
for x := 0 to Bitmap.Width - 1 do
begin
q.b := (x xor y) mod 255;
idx := y * LineLength + x;
LastLine [idx] := q;
end; // for
end; // for
Image.Picture.Assign (Bitmap);
finally
Bitmap.Free;
end; // try..finally
end;
这篇关于如何正确实现TBitmap的scanline访问?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!