在其他PNG上绘制PNG图像

Question

如何将两个PNG合并在一起？我知道你不能使用PNGObject.Draw，因为它不会复制alpha transaperncy（我不确定但它无论如何都不起作用）所以需要自定义过程/函数。我没有带着空手，我有这个程序：

procedure MergePNGLayer(Layer1,Layer2: TPNGObject; Const aLeft,aTop:Integer);
var
  x, y: Integer;
  SL1,  SL2,  SLBlended : pRGBLine;
  aSL1, aSL2, aSLBlended: PByteArray;
  blendCoeff: single;
  blendedPNG, Lay2buff: TPNGObject;
begin
  blendedPNG:=TPNGObject.Create;
  blendedPNG.Assign(Layer1);
  Lay2buff:=TPNGObject.Create;
  Lay2buff.Assign(Layer2);
  SetPNGCanvasSize(Layer2,Layer1.Width,Layer1.Height,aLeft,aTop);
  for y := 0 to Layer1.Height-1 do
  begin
    SL1 := Layer1.Scanline[y];
    SL2 := Layer2.Scanline[y];
    aSL1 := Layer1.AlphaScanline[y];
    aSL2 := Layer2.AlphaScanline[y];
    SLBlended := blendedPNG.Scanline[y];
    aSLBlended := blendedPNG.AlphaScanline[y];
    for x := 0 to Layer1.Width-1 do
    begin
      blendCoeff:=aSL1[x] * 100/255/100;
      aSLBlended[x] := round(aSL2[x] + (aSL1[x]-aSL2[x]) * blendCoeff);
      SLBlended[x].rgbtRed   := round(SL2[x].rgbtRed + (SL1[x].rgbtRed-SL2[x].rgbtRed) * blendCoeff);
      SLBlended[x].rgbtGreen := round(SL2[x].rgbtGreen + (SL1[x].rgbtGreen-SL2[x].rgbtGreen) * blendCoeff);
      SLBlended[x].rgbtBlue  := round(SL2[x].rgbtBlue + (SL1[x].rgbtBlue-SL2[x].rgbtBlue) * blendCoeff);
    end;
  end;
Layer1.Assign(blendedPNG);
Layer2.Assign(Lay2buff);
blendedPNG.Free;
Lay2buff.Free;
end;

但遗憾的是，它不应该如何运作，它可以完成工作，但不是正确的。当它将空图像与加载的图像合并时，它工作正常，但是当两个图像都不为空时，它会使它们失去透明度。

procedure TForm1.FormClick(Sender: TObject);
var
PNG1, PNG2, PNG3, Dest: TPNGObject;
begin
PNG1 := TPNGObject.Create;
PNG2 := TPNGObject.Create;
PNG3 := TPNGObject.Create;

PNG1.LoadFromFile('Aero\TopLeft.png');//Width 10
PNG2.LoadFromFile('Aero\Top.png');//Width 200
PNG3.LoadFromFile('Aero\TopRight.png');//Width 10

Dest := TPNGObject.CreateBlank(COLOR_RGBALPHA, 16, 220, 10);
MergePNGLayer(Dest, PNG1, 0, 0);
MergePNGLayer(Dest, PNG2, 10, 0);
MergePNGLayer(Dest, PNG3, 210, 0);
Dest.SaveToFile('C:\OUT.PNG');
end;

通缉结果：

实际结果：

我不确定你是否能看到这些imga之间的差异，但是你应该在PNG编辑器软件中打开它们，你会发现它们之间的区别。所以我需要其他程序来合并PNG。顺便提一下，我正在使用PNGImage的最新版本。

谢谢你，祝你有个美好的一天！

Answer 1

这似乎工作正常：

procedure DrawPngWithAlpha(Src, Dest: TPNGObject; const R: TRect);
var
  X, Y: Integer;
  Alpha: PByte;
begin
  Src.Draw(Dest.Canvas, R);

  // I have no idea why standard implementation of TPNGObject.Draw doesn't apply transparency.
  for Y := R.Top to R.Bottom - 1 do
    for X := R.Left to R.Right - 1 do
    begin
      Alpha := @Dest.AlphaScanline[Y]^[X];
      Alpha^ := Min(255, Alpha^ + Src.AlphaScanline[Y - R.Top]^[X - R.Left]);
    end;
end;