如何在图像(Jpg,Bmp)上编写半透明文本,或者透明文本(颜色与背景图像相同),但带有阴影,我想要做的是给图像打水印。
我想使用Delphi win32实现这一目标。
如何在图像(Jpg,Bmp)上编写半透明文本,或者透明文本(颜色与背景图像相同),但带有阴影,我想要做的是给图像打水印。
我想使用Delphi win32实现这一目标。
一种选择是使用Windows.pas单元中的AlphaBlend函数。像这样可以产生半透明文本(带有阴影 - 建立在Jim McKeeth的响应之上),覆盖在图像上:
uses Windows, Graphics;
.
.
.
var
BackgroundImage: Graphics.TBitmap; { need to call out specifically for Graphics.TBitmap
because the Windows unit also has a TBitmap
declaration }
TextImage: Graphics.TBitmap;
BlendFunc: BLENDFUNCTION;
begin
BlendFunc.BlendOp := AC_SRC_OVER;
BlendFunc.BlendFlags := 0;
BlendFunc.SourceConstantAlpha := $C0; { a hex value from $00-$FF (0-255).
Represents the percent of opaqueness:
$00 is completely transparent,
$FF is completely opaque.
$C0 is 75% opaque }
BlendFunc.AlphaFormat := AC_SRC_ALPHA;
{ BackgroundImage is for holding the image you want to overlay text onto }
BackgroundImage := Graphics.TBitmap.Create;
try
BackgroundImage.LoadFromFile('yourimagehere.bmp');
{ Create another TBitmap to hold the text you want to overlay }
TextImage := Graphics.TBitmap.Create;
try
{ Set this bitmap to have the same dimensions as the
background image you want the text to appear on. }
TextImage.Height := BackgroundImage.Height;
TextImage.Width := BackgroundImage.Width;
{ In my limited experience with AlphaBlend, Black is always 100%
transparent. So, paint TextImage completely Black. Play around
with this to see the effect it has on the final outcome. }
TextImage.Canvas.Brush.Color := clBlack;
TextImage.Canvas.FloodFill(0, 0, clNone, fsBorder);
TextImage.Canvas.Font.Style := [fsBold];
{ Write the shadow first }
TextImage.Canvas.Brush.Style := bsClear;
TextImage.Canvas.Font.Color := clDkGray;
TextImage.Canvas.TextOut(11, 11, 'Test');
{ Then put the text on top (slightly offset) }
TextImage.Canvas.Brush.Style := bsClear;
TextImage.Canvas.Font.Color := clMaroon;
TextImage.Canvas.TextOut(10, 10, 'Test');
{ Use the AlphaBlend function to overlay the bitmap holding the text
on top of the bitmap holding the original image. }
Windows.AlphaBlend(BackgroundImage.Canvas.Handle, 0, 0,
TextImage.Width, TextImage.Height,
TextImage.Canvas.Handle, 0, 0, TextImage.Width,
TextImage.Height, BlendFunc);
{ Assign the now updated BackgroundImage to a TImage control for display }
Image1.Picture.Bitmap.Assign(BackgroundImage);
finally
TextImage.Free;
end;
finally
BackgroundImage.Free;
end;
end;
我猜测你想要实现的不仅仅是在透明背景上写入文本,而是希望在图像上写入某种形式的 alpha-blended 文本。
最简单的方法是利用 GDI+ 函数。它们已经被封装在 Delphi 中,并可以从 http://www.progdigy.com/ 下载。那里有许多示例可供参考。
// Bold shows up better when over an image
image1.Canvas.Font.Style := [fsBold];
// Write the shadow first
image1.Canvas.Brush.Style:=bsClear;
image1.Canvas.Font.Color := clGrayText;
image1.Canvas.TextOut(1, 1, 'hi there');
// Then put the text on top (slightly offset)
image1.Canvas.Brush.Style:=bsClear;
image1.Canvas.Font.Color :=clBlack;
image1.Canvas.TextOut(0, 0, 'hi there');
这是一个具有透明背景的文本。或者你想让文本本身半透明?这有点棘手。您需要手动绘制它。相反,一个简单的方法是采样图像上写作区域的颜色平均值。然后将字体颜色设置为稍微浅一些,阴影设置为稍微深一些。然后它就会有点融合在一起。
img.Canvas.Brush.Style:=bsClear;
img.Canvas.Font.Color:=clBlack;
img.Canvas.TextOut(0, 0, 'hi there');
这个函数基于Dave Elsberry的思路。
与原版不同之处:
{-------------------------------------------------------------------------------------------------------------
DrawTextShadowBox
Draws text in a semi-transparent rectangle with shadow text.
The shadow text is blended to the background and then blurred.
Variant:
1: Draws text in a box that is as wide as the BMP and can be aligned to top or bottom
2: Draws text in a box that is as wide as text and is placed into the image at coordinates x,y
Parameters:
Opacity a value from 0-255. 0 => Shadow is completelly transparent
To set the Font color/size, the caller should do: aCanvas.Font.Size:= x
Issues:
The blurring function cuts too suddenly. The rectangle that was blurred is too visible. Do a blur that slowly fades at the edges.
Might be slow becuase of the alpha blending and because of the blur.
Important!
The input img must be pf24bit.
When the AlphaFormat member is AC_SRC_ALPHA, the source bitmap must be 32 bpp. If it is not, the AlphaBlend function will fail.
-------------------------------------------------------------------------------------------------------------}
procedure DrawTextShadowBox(BMP: TBitmap; CONST Text: string; AlignTop: Boolean; ShadowColor: TColor= clTextShadow; ShadowOpacity: Byte= 20; Blur: Byte= 2);
VAR
Shadow: Vcl.Graphics.TBitmap;
BlendFunc: BLENDFUNCTION;
x, y: Integer;
BmpRect: TRect; { Rectangle in the original bitmap where we want to draw the shadowed text }
ShadowRect: TRect;
TextWidth, TextHeight: Integer;
OriginalColor: TColor;
begin
Assert(BMP.PixelFormat= pf24bit, 'Wrong pixel format!!');
OriginalColor:= bmp.Canvas.Font.Color;
TextWidth := BMP.Canvas.TextWidth (Text);
TextHeight:= BMP.Canvas.TextHeight(Text);
{ Write the shadow on a separate bitmap (overlay) }
Shadow := TBitmap.Create;
TRY
{ Bitmap setup }
Shadow.Canvas.Font.Assign(BMP.Canvas.Font);
Shadow.PixelFormat:= pf24bit;
Shadow.SetSize(BMP.Width, TextHeight);
{ Bitmap rectangle as big as ShadowBMP }
ShadowRect.Left:= 0;
ShadowRect.Top := 0;
ShadowRect.Right := Shadow.Width;
ShadowRect.Bottom:= Shadow.Height;
{ Fill shadow rectangle }
Shadow.Canvas.Brush.Color := clBlack; { In AlphaBlend, Black is always 100% transparent. So, paint Shadow completely Black. }
Shadow.Canvas.FillRect(ShadowRect);
BmpRect.Left := 0;
BmpRect.Right := Shadow.Width;
if AlignTop
then BmpRect.Top := 0
else BmpRect.Top := BMP.Height- TextHeight;
BmpRect.Bottom:= BmpRect.Top+ TextHeight;
{ Blend rectangle with orig image } { Use the AlphaBlend function to overlay the bitmap holding the text on top of the bitmap holding the original image. }
BlendFunc.BlendOp := AC_SRC_OVER;
BlendFunc.BlendFlags := 0;
BlendFunc.SourceConstantAlpha := ShadowOpacity;
BlendFunc.AlphaFormat := 0; //AC_SRC_ALPHA; // if I put this back, the shadow will be completly invisible when merged with a white source image
WinApi.Windows.AlphaBlend(BMP.Canvas.Handle, BmpRect.Left, BmpRect.Top, BmpRect.Right, TextHeight, Shadow.Canvas.Handle, 0, 0, Shadow.Width, Shadow.Height, BlendFunc);
{ Copy the blended area back to the Shadow bmp }
Shadow.Canvas.CopyRect(ShadowRect, BMP.Canvas, BmpRect);
{ Diagonal shadow }
x:= (BMP.Width - TextWidth) DIV 2; // Find center
Shadow.Canvas.Brush.Style:= bsClear;
Shadow.Canvas.Font.Color := ShadowColor;
Shadow.Canvas.TextOut(x, 0, Text);
{ Blur the shadow }
janFX.GaussianBlur(Shadow, Blur, 1);
{ Paste it back }
BMP.Canvas.CopyRect(BmpRect, Shadow.Canvas, ShadowRect);
FINALLY
FreeAndNil(Shadow);
END;
{ Draw actual text at 100% opacity }
if AlignTop
then y := 0
else y := BMP.Height- TextHeight;
BMP.Canvas.Brush.Style:= bsClear;
BMP.Canvas.Font.Color := OriginalColor;
BMP.Canvas.TextOut(x, y, Text);
end;
procedure DrawTextShadowBox(aCanvas: TCanvas; CONST Text: string; X, Y: Integer; ShadowColor: TColor= clTextShadow; ShadowOpacity: Byte= 20; Blur: Byte= 2);
VAR
Shadow: Vcl.Graphics.TBitmap;
BlendFunc: BLENDFUNCTION;
H, W: Integer;
OriginalColor: TColor;
R, R2: TRect;
CONST Edge= 5;
begin
OriginalColor:= aCanvas.Font.Color;
{ Write the shadow on a separate bitmap (overlay) }
Shadow := TBitmap.Create;
TRY
{ Assign font }
Shadow.Canvas.Font.Assign(aCanvas.Font);
Shadow.PixelFormat:= pf24bit;
{ Compute overlay size }
W:= Shadow.Canvas.TextWidth (Text);
H:= Shadow.Canvas.TextHeight(Text);
Shadow.SetSize(W, H);
{ Fill shadow rectangle }
R:= Rect(0, 0, Shadow.Width, Shadow.Height);
Shadow.Canvas.Brush.Color := clBlack; { In AlphaBlend, Black is always 100% transparent. So, paint Shadow completely Black. }
Shadow.Canvas.FillRect(R);
{ Blend rectangle with orig image } { Use the AlphaBlend function to overlay the bitmap holding the text on top of the bitmap holding the original image. }
BlendFunc.BlendOp := AC_SRC_OVER;
BlendFunc.BlendFlags := 0;
BlendFunc.SourceConstantAlpha := ShadowOpacity;
BlendFunc.AlphaFormat := 0; //AC_SRC_ALPHA; // if I put this back, the shadow will be completly invisible when merged with a white source image
WinApi.Windows.AlphaBlend(aCanvas.Handle, x, y, Shadow.Width, Shadow.Height, Shadow.Canvas.Handle, 0, 0, Shadow.Width, Shadow.Height, BlendFunc);
{ Copy the blended area back to the Shadow bmp }
R2:= rect(x, y, x+Shadow.Width, y+Shadow.Height);
Shadow.Canvas.CopyRect(R, aCanvas, R2);
{ Diagonal shadow }
Shadow.Canvas.Brush.Style:= bsClear;
Shadow.Canvas.Font.Color := ShadowColor;
Shadow.Canvas.TextOut(0, 0, Text);
{ Blur the shadow }
janFX.GaussianBlur(Shadow, blur, 1);
{ Paste it back }
aCanvas.CopyRect(R2, Shadow.Canvas, R);
FINALLY
FreeAndNil(Shadow);
END;
{ Draw actual text at 100% opacity }
aCanvas.Brush.Style:= bsClear;
aCanvas.Font.Color := OriginalColor;
aCanvas.TextOut(x, y, Text);
end;
procedure TfrmTest.UseIt;
VAR BackgroundImage: tbitmap;
begin
BackgroundImage := Graphics.TBitmap.Create;
try
BackgroundImage.LoadFromFile('c:\test.bmp');
DrawShadowText (BackgroundImage.Canvas, 'This is some demo text', 20, 40, 140, clRed, clSilver);
Image1.Picture.Bitmap.Assign(BackgroundImage);
FINALLY
BackgroundImage.Free;
end;
end;