曾几何时，阅读这个问题，我想知道如何在不摆弄所有位的情况下将位图旋转任意角度。最近，其他人也有明显的困难。
已经有很多关于以 90° 间隔旋转的问题，最值得注意的是这个，但我想旋转一个真实的角度。最好可以通过旋转来调整图像大小，并为将添加到图像表面的部分设置自定义（透明）背景颜色。然后我假设例程的签名看起来像：
procedure RotateBitmap(Bmp: TBitmap; Angle: Single; AdjustSize: Boolean;
BackColor: TColor);
这些答案提到了构建此例程的以下候选对象：SetWorldTransform、PlgBlt、GDI+，但我希望看到一个（有效的）实现。
tl;博士; 使用 GDI+
使用 WinAPI 的SetWorldTransform，您可以转换设备上下文的空间：旋转、剪切、偏移和缩放。这是通过设置 XFORM 类型的变换矩阵的成员来完成的。根据文档填写其成员。
procedure RotateBitmap(Bmp: TBitmap; Rads: Single; AdjustSize: Boolean;
BkColor: TColor = clNone);
var
C: Single;
S: Single;
XForm: tagXFORM;
Tmp: TBitmap;
begin
C := Cos(Rads);
S := Sin(Rads);
XForm.eM11 := C;
XForm.eM12 := S;
XForm.eM21 := -S;
XForm.eM22 := C;
Tmp := TBitmap.Create;
try
Tmp.TransparentColor := Bmp.TransparentColor;
Tmp.TransparentMode := Bmp.TransparentMode;
Tmp.Transparent := Bmp.Transparent;
Tmp.Canvas.Brush.Color := BkColor;
if AdjustSize then
begin
Tmp.Width := Round(Bmp.Width * Abs(C) + Bmp.Height * Abs(S));
Tmp.Height := Round(Bmp.Width * Abs(S) + Bmp.Height * Abs(C));
XForm.eDx := (Tmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
XForm.eDy := (Tmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end
else
begin
Tmp.Width := Bmp.Width;
Tmp.Height := Bmp.Height;
XForm.eDx := (Bmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
XForm.eDy := (Bmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end;
SetGraphicsMode(Tmp.Canvas.Handle, GM_ADVANCED);
SetWorldTransform(Tmp.Canvas.Handle, XForm);
BitBlt(Tmp.Canvas.Handle, 0, 0, Tmp.Width, Tmp.Height, Bmp.Canvas.Handle,
0, 0, SRCCOPY);
Bmp.Assign(Tmp);
finally
Tmp.Free;
end;
end;
PlgBlt函数执行从源设备上下文中的指定矩形到目标设备上下文中的指定平行四边形的位块传输。lpPoint通过参数映射源图像的角点。
procedure RotateBitmap(Bmp: TBitmap; Rads: Single; AdjustSize: Boolean;
BkColor: TColor = clNone);
var
C: Single;
S: Single;
Tmp: TBitmap;
OffsetX: Single;
OffsetY: Single;
Points: array[0..2] of TPoint;
begin
C := Cos(Rads);
S := Sin(Rads);
Tmp := TBitmap.Create;
try
Tmp.TransparentColor := Bmp.TransparentColor;
Tmp.TransparentMode := Bmp.TransparentMode;
Tmp.Transparent := Bmp.Transparent;
Tmp.Canvas.Brush.Color := BkColor;
if AdjustSize then
begin
Tmp.Width := Round(Bmp.Width * Abs(C) + Bmp.Height * Abs(S));
Tmp.Height := Round(Bmp.Width * Abs(S) + Bmp.Height * Abs(C));
OffsetX := (Tmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
OffsetY := (Tmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end
else
begin
Tmp.Width := Bmp.Width;
Tmp.Height := Bmp.Height;
OffsetX := (Bmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
OffsetY := (Bmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end;
Points[0].X := Round(OffsetX);
Points[0].Y := Round(OffsetY);
Points[1].X := Round(OffsetX + Bmp.Width * C);
Points[1].Y := Round(OffsetY + Bmp.Width * S);
Points[2].X := Round(OffsetX - Bmp.Height * S);
Points[2].Y := Round(OffsetY + Bmp.Height * C);
PlgBlt(Tmp.Canvas.Handle, Points, Bmp.Canvas.Handle, 0, 0, Bmp.Width,
Bmp.Height, 0, 0, 0);
Bmp.Assign(Tmp);
finally
Tmp.Free;
end;
end;
Graphics32是一个专为快速位图处理而设计的库。它需要一些经验才能充分发挥其潜力，但文档和提供的示例应该可以帮助您入门。
图像的旋转TBitmap32是通过许多可用的转换类之一对其进行转换来完成的。这里需要这个TAffineTransformation类。首先，将图像大小的一半移到左上角，然后旋转并将结果移回右下角，可能使用新的图像尺寸。
uses
GR32, GR32_Transforms;
procedure RotateBitmap(Bmp: TBitmap32; Degs: Integer; AdjustSize: Boolean;
BkColor: TColor = clNone; Transparent: Boolean = False); overload;
var
Tmp: TBitmap32;
Transformation: TAffineTransformation;
begin
Tmp := TBitmap32.Create;
Transformation := TAffineTransformation.Create;
try
Transformation.BeginUpdate;
Transformation.SrcRect := FloatRect(0, 0, Bmp.Width, Bmp.Height);
Transformation.Translate(-0.5 * Bmp.Width, -0.5 * Bmp.Height);
Transformation.Rotate(0, 0, -Degs);
if AdjustSize then
with Transformation.GetTransformedBounds do
Tmp.SetSize(Round(Right - Left), Round(Bottom - Top))
else
Tmp.SetSize(Bmp.Width, Bmp.Height);
Transformation.Translate(0.5 * Tmp.Width, 0.5 * Tmp.Height);
Transformation.EndUpdate;
Tmp.Clear(Color32(BkColor));
if not Transparent then
Bmp.DrawMode := dmTransparent;
Transform(Tmp, Bmp, Transformation);
Bmp.Assign(Tmp);
Bmp.OuterColor := Color32(BkColor);
if Transparent then
Bmp.DrawMode := dmTransparent;
finally
Transformation.Free;
Tmp.Free;
end;
end;
procedure RotateBitmap(Bmp: TBitmap; Degs: Integer; AdjustSize: Boolean;
BkColor: TColor = clNone); overload;
var
Tmp: TBitmap32;
Transparent: Boolean;
begin
Tmp := TBitmap32.Create;
try
Transparent := Bmp.Transparent;
Tmp.Assign(Bmp);
RotateBitmapGR32(Tmp, Degs, AdjustSize, BkColor, Transparent);
Bmp.Assign(Tmp);
if Transparent then
Bmp.Transparent := True;
finally
Tmp.Free;
end;
end;
在 Windows XP 中引入的 Microsoft 的GDI+ API 比默认的 GDI API 更有效。对于 Delphi 2009 及更高版本，可从此处获得该库。对于较旧的 Delphi 版本，该库可从此处获得。
在 GDI+ 中，旋转也是由变换矩阵完成的。绘图的工作方式完全不同。创建一个TGPGraphics对象并使用其构造函数将其附加到设备上下文。随后，对象上的绘图操作由 API 翻译，并将输出到目标上下文。
uses
GDIPOBJ, GDIPAPI; // < D2009
GdiPlus; // >= D2009
procedure RotateBitmap(Bmp: TBitmap; Degs: Integer; AdjustSize: Boolean;
BkColor: TColor = clNone);
var
Tmp: TGPBitmap;
Matrix: TGPMatrix;
C: Single;
S: Single;
NewSize: TSize;
Graphs: TGPGraphics;
P: TGPPointF;
begin
Tmp := TGPBitmap.Create(Bmp.Handle, Bmp.Palette);
Matrix := TGPMatrix.Create;
try
Matrix.RotateAt(Degs, MakePoint(0.5 * Bmp.Width, 0.5 * Bmp.Height));
if AdjustSize then
begin
C := Cos(DegToRad(Degs));
S := Sin(DegToRad(Degs));
NewSize.cx := Round(Bmp.Width * Abs(C) + Bmp.Height * Abs(S));
NewSize.cy := Round(Bmp.Width * Abs(S) + Bmp.Height * Abs(C));
Bmp.Width := NewSize.cx;
Bmp.Height := NewSize.cy;
end;
Graphs := TGPGraphics.Create(Bmp.Canvas.Handle);
try
Graphs.Clear(ColorRefToARGB(ColorToRGB(BkColor)));
Graphs.SetTransform(Matrix);
Graphs.DrawImage(Tmp, (Cardinal(Bmp.Width) - Tmp.GetWidth) div 2,
(Cardinal(Bmp.Height) - Tmp.GetHeight) div 2);
finally
Graphs.Free;
end;
finally
Matrix.Free;
Tmp.Free;
end;
end;
上面的例程保留了 fead 位图的透明设置，除了需要附加Transparent参数的 Graphics32 解决方案。
我编写了一个测试应用程序（参见下面的完整代码）来调整各种方法的性能并比较生成的图像质量。
第一个也是最重要的结论是 GDI+ 使用了其他没有的抗锯齿，从而产生了最好的图像质量。（我尝试通过设置CompositingQuality、InterpolationMode、SmoothingMode和来防止抗锯齿但未成功PixelOffsetMode，因此当不首选抗锯齿时，请不要使用 GDI+。）
此外，到目前为止，GDI+ 解决方案也是最快的方法。
unit RotateTestForm;
interface
uses
Windows, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, ExtCtrls,
JPEG, Math, GR32, GR32_Transforms, GDIPOBJ, GDIPAPI {, GdiPlus};
type
TTestForm = class(TForm)
private
FImage: TImage;
FOpenDialog: TOpenDialog;
procedure FormPaint(Sender: TObject);
public
constructor Create(AOwner: TComponent); override;
end;
var
TestForm: TTestForm;
implementation
{$R *.dfm}
procedure RotateBitmapSWT(Bmp: TBitmap; Rads: Single; AdjustSize: Boolean;
BkColor: TColor = clNone);
var
C: Single;
S: Single;
XForm: TXForm;
Tmp: TBitmap;
begin
C := Cos(Rads);
S := Sin(Rads);
XForm.eM11 := C;
XForm.eM12 := S;
XForm.eM21 := -S;
XForm.eM22 := C;
Tmp := TBitmap.Create;
try
Tmp.TransparentColor := Bmp.TransparentColor;
Tmp.TransparentMode := Bmp.TransparentMode;
Tmp.Transparent := Bmp.Transparent;
Tmp.Canvas.Brush.Color := BkColor;
if AdjustSize then
begin
Tmp.Width := Round(Bmp.Width * Abs(C) + Bmp.Height * Abs(S));
Tmp.Height := Round(Bmp.Width * Abs(S) + Bmp.Height * Abs(C));
XForm.eDx := (Tmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
XForm.eDy := (Tmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end
else
begin
Tmp.Width := Bmp.Width;
Tmp.Height := Bmp.Height;
XForm.eDx := (Bmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
XForm.eDy := (Bmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end;
SetGraphicsMode(Tmp.Canvas.Handle, GM_ADVANCED);
SetWorldTransform(Tmp.Canvas.Handle, XForm);
BitBlt(Tmp.Canvas.Handle, 0, 0, Tmp.Width, Tmp.Height, Bmp.Canvas.Handle,
0, 0, SRCCOPY);
Bmp.Assign(Tmp);
finally
Tmp.Free;
end;
end;
procedure RotateBitmapPLG(Bmp: TBitmap; Rads: Single; AdjustSize: Boolean;
BkColor: TColor = clNone);
var
C: Single;
S: Single;
Tmp: TBitmap;
OffsetX: Single;
OffsetY: Single;
Points: array[0..2] of TPoint;
begin
C := Cos(Rads);
S := Sin(Rads);
Tmp := TBitmap.Create;
try
Tmp.TransparentColor := Bmp.TransparentColor;
Tmp.TransparentMode := Bmp.TransparentMode;
Tmp.Transparent := Bmp.Transparent;
Tmp.Canvas.Brush.Color := BkColor;
if AdjustSize then
begin
Tmp.Width := Round(Bmp.Width * Abs(C) + Bmp.Height * Abs(S));
Tmp.Height := Round(Bmp.Width * Abs(S) + Bmp.Height * Abs(C));
OffsetX := (Tmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
OffsetY := (Tmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end
else
begin
Tmp.Width := Bmp.Width;
Tmp.Height := Bmp.Height;
OffsetX := (Bmp.Width - Bmp.Width * C + Bmp.Height * S) / 2;
OffsetY := (Bmp.Height - Bmp.Width * S - Bmp.Height * C) / 2;
end;
Points[0].X := Round(OffsetX);
Points[0].Y := Round(OffsetY);
Points[1].X := Round(OffsetX + Bmp.Width * C);
Points[1].Y := Round(OffsetY + Bmp.Width * S);
Points[2].X := Round(OffsetX - Bmp.Height * S);
Points[2].Y := Round(OffsetY + Bmp.Height * C);
PlgBlt(Tmp.Canvas.Handle, Points, Bmp.Canvas.Handle, 0, 0, Bmp.Width,
Bmp.Height, 0, 0, 0);
Bmp.Assign(Tmp);
finally
Tmp.Free;
end;
end;
procedure RotateBitmapGR32(Bmp: TBitmap32; Degs: Integer; AdjustSize: Boolean;
BkColor: TColor = clNone; Transparent: Boolean = False); overload;
var
Tmp: TBitmap32;
Transformation: TAffineTransformation;
begin
Tmp := TBitmap32.Create;
Transformation := TAffineTransformation.Create;
try
Transformation.BeginUpdate;
Transformation.SrcRect := FloatRect(0, 0, Bmp.Width, Bmp.Height);
Transformation.Translate(-0.5 * Bmp.Width, -0.5 * Bmp.Height);
Transformation.Rotate(0, 0, -Degs);
if AdjustSize then
with Transformation.GetTransformedBounds do
Tmp.SetSize(Round(Right - Left), Round(Bottom - Top))
else
Tmp.SetSize(Bmp.Width, Bmp.Height);
Transformation.Translate(0.5 * Tmp.Width, 0.5 * Tmp.Height);
Transformation.EndUpdate;
Tmp.Clear(Color32(BkColor));
if not Transparent then
Bmp.DrawMode := dmTransparent;
Transform(Tmp, Bmp, Transformation);
Bmp.Assign(Tmp);
Bmp.OuterColor := Color32(BkColor);
if Transparent then
Bmp.DrawMode := dmTransparent;
finally
Transformation.Free;
Tmp.Free;
end;
end;
procedure RotateBitmapGR32(Bmp: TBitmap; Degs: Integer; AdjustSize: Boolean;
BkColor: TColor = clNone); overload;
var
Tmp: TBitmap32;
Transparent: Boolean;
begin
Tmp := TBitmap32.Create;
try
Transparent := Bmp.Transparent;
Tmp.Assign(Bmp);
RotateBitmapGR32(Tmp, Degs, AdjustSize, BkColor, Transparent);
Bmp.Assign(Tmp);
if Transparent then
Bmp.Transparent := True;
finally
Tmp.Free;
end;
end;
procedure RotateBitmapGDIP(Bmp: TBitmap; Degs: Integer; AdjustSize: Boolean;
BkColor: TColor = clNone);
var
Tmp: TGPBitmap;
Matrix: TGPMatrix;
C: Single;
S: Single;
NewSize: TSize;
Graphs: TGPGraphics;
P: TGPPointF;
begin
Tmp := TGPBitmap.Create(Bmp.Handle, Bmp.Palette);
Matrix := TGPMatrix.Create;
try
Matrix.RotateAt(Degs, MakePoint(0.5 * Bmp.Width, 0.5 * Bmp.Height));
if AdjustSize then
begin
C := Cos(DegToRad(Degs));
S := Sin(DegToRad(Degs));
NewSize.cx := Round(Bmp.Width * Abs(C) + Bmp.Height * Abs(S));
NewSize.cy := Round(Bmp.Width * Abs(S) + Bmp.Height * Abs(C));
Bmp.Width := NewSize.cx;
Bmp.Height := NewSize.cy;
end;
Graphs := TGPGraphics.Create(Bmp.Canvas.Handle);
try
Graphs.Clear(ColorRefToARGB(ColorToRGB(BkColor)));
Graphs.SetTransform(Matrix);
Graphs.DrawImage(Tmp, (Cardinal(Bmp.Width) - Tmp.GetWidth) div 2,
(Cardinal(Bmp.Height) - Tmp.GetHeight) div 2);
finally
Graphs.Free;
end;
finally
Matrix.Free;
Tmp.Free;
end;
end;
{ TTestForm }
constructor TTestForm.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
Font.Name := 'Tahoma';
Top := 0;
ClientWidth := 560;
ClientHeight := 915;
Show;
FImage := TImage.Create(Self);
FOpenDialog := TOpenDialog.Create(Self);
FOpenDialog.Title := 'Select an small sized image (min. 100 x 100)';
FOpenDialog.Options := FOpenDialog.Options + [ofFileMustExist];
FOpenDialog.Filter := 'JPEG|*.JPG|BMP|*.BMP';
if FOpenDialog.Execute then
begin
FImage.Picture.LoadFromFile(FOpenDialog.FileName);
OnPaint := FormPaint;
Invalidate;
end
else
Application.Terminate;
end;
procedure TTestForm.FormPaint(Sender: TObject);
var
Img: TBitmap;
Bmp: TBitmap;
Bmp32: TBitmap32;
BkColor: TColor;
AdjustSize: Boolean;
Degs: Integer;
Rads: Single;
RotCount: Integer;
I: Integer;
Tick: Cardinal;
begin
Img := TBitmap.Create;
Bmp := TBitmap.Create;
Bmp32 := TBitmap32.Create;
try
BkColor := clBtnFace;
Img.Canvas.Brush.Color := BkColor;
Img.Width := 100;
Img.Height := 100;
Img.Canvas.Draw(0, 0, FImage.Picture.Graphic);
AdjustSize := False;
Degs := 45;
Rads := DegToRad(Degs);
RotCount := 1000;
Canvas.TextOut(10, 10, 'Original:');
Canvas.Draw(10, 30, Img);
Canvas.TextOut(10, 140, Format('Size = %d x %d', [Img.Width, Img.Height]));
Canvas.TextOut(10, 160, Format('Angle = %d°', [Degs]));
Canvas.TextOut(10, 250, Format('%d rotations:', [RotCount]));
Canvas.TextOut(120, 10, 'SetWorldTransform:');
Bmp.Assign(Img);
RotateBitmapSWT(Bmp, Rads, AdjustSize, BkColor);
Canvas.Draw(120, 30, Bmp);
if not AdjustSize then
begin
Tick := GetTickCount;
for I := 0 to RotCount - 2 do
RotateBitmapSWT(Bmp, Rads, AdjustSize, BkColor);
Canvas.TextOut(120, 250, Format('%d msec', [GetTickCount - Tick]));
Canvas.Draw(120, 140, Bmp);
end;
Canvas.TextOut(230, 10, 'PlgBlt:');
Bmp.Assign(Img);
RotateBitmapPLG(Bmp, Rads, AdjustSize, BkColor);
Canvas.Draw(230, 30, Bmp);
if not AdjustSize then
begin
Tick := GetTickCount;
for I := 0 to RotCount - 2 do
RotateBitmapPLG(Bmp, Rads, AdjustSize, BkColor);
Canvas.TextOut(230, 250, Format('%d msec', [GetTickCount - Tick]));
Canvas.Draw(230, 140, Bmp);
end;
Canvas.TextOut(340, 10, 'Graphics32:');
Bmp.Assign(Img);
RotateBitmapGR32(Bmp, Degs, AdjustSize, BkColor);
Canvas.Draw(340, 30, Bmp);
if not AdjustSize then
begin
Tick := GetTickCount;
for I := 0 to RotCount - 2 do
RotateBitmapGR32(Bmp, Degs, AdjustSize, BkColor);
Canvas.TextOut(340, 250, Format('%d msec', [GetTickCount - Tick]));
Canvas.Draw(340, 140, Bmp);
// Without in between conversion to TBitmap:
Bmp32.Assign(Img);
Tick := GetTickCount;
for I := 0 to RotCount - 1 do
RotateBitmapGR32(Bmp32, Degs, AdjustSize, BkColor, False);
Canvas.TextOut(340, 270, Format('%d msec (optimized)',
[GetTickCount - Tick]));
end;
Canvas.TextOut(450, 10, 'GDI+ :');
Bmp.Assign(Img);
RotateBitmapGDIP(Bmp, Degs, AdjustSize, BkColor);
Canvas.Draw(450, 30, Bmp);
if not AdjustSize then
begin
Tick := GetTickCount;
for I := 0 to RotCount - 2 do
RotateBitmapGDIP(Bmp, Degs, AdjustSize, BkColor);
Canvas.TextOut(450, 250, Format('%d msec', [GetTickCount - Tick]));
Canvas.Draw(450, 140, Bmp);
end;
finally
Bmp32.Free;
Bmp.Free;
Img.Free;
OnPaint := nil;
end;
end;
end.
如果有人正在研究图像旋转，他们可能还会查看 Mitov 视频库（非商业用途免费：链接）。VCL 和 FireMonkey。它处理所有低级细节，这让我们避免了 NGLN 的优秀答案探索的那种详细编码。
过去两年我们一直在使用它，并且在我们的商业应用程序中对它非常满意。
它有一个旋转组件，可以处理静态图像和视频流。他们的库是完全多任务的，可以选择使用所有可用的内核和低级原语，在带有英特尔自己的性能库的英特尔芯片组上 ( http://software.intel.com/en-us/articles/intel-ipp )
在中等硬件上，我们可以运行多个视频或 bmp 流，我们可以在像素级别实时旋转、剪辑、缩放和处理这些流。