任何人都可以帮我找到一个能够在保持透明度的同时快速旋转PNG图像的组件或SDK吗？
答案 0 :(得分：3)
PNGImage组件的原始作者（Delphi本机组件的基础）有一个论坛，他和其他人发布了关于如何使用PNGImage组件执行操作的代码片段。
在论坛被删除之前，我抓住了所有代码片段的副本，并将它们放在CodeGear Code Central网站上。
大多数（如果不是全部）都可以使用本机PNG图像并保持Alpha通道。
以下是包中包含的完整示例列表：
Smooth rotates a PNG object
Resizes a TPNGObject using a smooth algorithm
Slice one PNG into several smaller ones
Saves an image as either a bitmap or a png.
Sample chunk descendant
Read all tEXt-Chunks and write values into a TStrings object
Display a message box with information extracted from the PNG File
Finds and cuts a block from a PNG image
This method converts the png into a jpeg object
This method converts the png into a bmp object
Overlay one PNG over another
This makes the image half transparent
Flips a png image vertically and saves back
Draws a png image over the desktop
以下是链接：CodeCentral PNG Methods
修改
这是RotatePNG功能的高度优化版本。 从技术上讲，它仍然是逐像素的，但它使用了许多技术，例如扫描线，指针数学和图像尺寸的存储，以实现适当的速度增加。
我使用2550x3300像素图像（~5MB）进行测试，并使用半粗略但完全（非）科学计算（在我脑海中计算），我想出了以下指标：
the old routine (mentioned above):的 ~7 seconds
the new routine (code below):的 ~1.5 seconds
我不能严格对此予以赞扬。代码最初来自EFG's website，我决定尝试将其中一个例程转换为旋转PNG图像而不是位图。
我敢肯定，任何了解此类事情的人都会看一下代码并提供一些建议来调整更快的速度。
procedure RotatePNG(
const PNGOriginal:TPNGImage;//input PNG
out PNGRotated:TPNGImage; //output PNG
Const Angle : double);
{
(c) har*GIS L.L.C., 1999
You are free to use this in any way, but please retain this comment block.
Please email questions to jim@har-gis.com .
Doc & Updates: http://www.efg2.com/Lab/ImageProcessing/RotateScanline.htm
and http://www.efg2.com/Lab/Library/Delphi/Graphics/JimHargis_RotateBitMap.zip
}
{
Modified by R.J.Mills, 2012 -
- Use pointer arithmetic instead of type sub-scripting for faster pixels.
- Converted to rotate PNG images June 2012.
}
Type
TRGBTripleArray = array [0..32767] of TRGBTriple; //allow integer subscript
pRGBTripleArray = ^TRGBTripleArray;
VAR
wPng : TPngImage;
theta:Double; // rotn angle in radians counterclockwise in windows
cosTheta : Single; {in windows}
sinTheta : Single;
i : INTEGER;
iOriginal : INTEGER;
iPrime : INTEGER;
j : INTEGER;
jOriginal : INTEGER;
jPrime : INTEGER;
NewWidth,NewHeight:INTEGER;
nBytes: Integer;//no. bytes per pixelformat
Oht,Owi,Rht,Rwi: Integer;//Original and Rotated subscripts to bottom/right
RowSizeRot : integer;
RowSizeOrg : integer;
AlphaSizeRot : integer;
AlphaSizeOrg : integer;
RowStartPtr : Pointer;
AlphaStartPtr : Pointer;
RowRotatedT: pRGBtripleArray; //3 bytes
AlphaRowT: pByteArray; //1 byte
AlphaRotatedT : pByteArray; //1 byte
TransparentT: TRGBTriple;
{=======================================}
function Mod360( const angle:Double ):Double;
begin
result := frac( angle/360 )*360;
if result < 0 then
result := result+360;
end;
{=======================================}
begin
Theta := -(2*pi* Mod360(angle))/360;
sinTheta := SIN( theta );
cosTheta := COS( theta );
NewWidth := ABS( ROUND( PNGOriginal.Height*sinTheta) ) + ABS( ROUND( PNGOriginal.Width*cosTheta ) );
NewHeight := ABS( ROUND( PNGOriginal.Width*sinTheta ) ) + ABS( ROUND( PNGOriginal.Height*cosTheta) );
if ( ABS(theta)*MAX( PNGOriginal.width,PNGOriginal.height ) ) > 1 then
begin//non-zero rotation
wPng := TPngImage.createblank(PNGOriginal.Header.ColorType, 8, NewWidth, NewHeight);
try
//local constants for loop, each was hit at least width*height times 1/8/00
Rwi := NewWidth - 1; //right column index
Rht := NewHeight - 1;//bottom row index
Owi := PNGOriginal.Width - 1; //transp color column index
Oht := PNGOriginal.Height - 1; //transp color row index
RowRotatedT := wPng.Scanline[ Rht ] ;
RowStartPtr := PNGOriginal.Scanline[ 0 ];
RowSizeRot := Integer(wPng.ScanLine[1])-Integer(wPng.ScanLine[0]);
RowSizeOrg := Integer(PNGOriginal.ScanLine[1])-Integer(PNGOriginal.ScanLine[0]);
TransparentT := pRGBtripleArray( PNGOriginal.Scanline[ Oht ] )[0];
if PNGOriginal.Header.ColorType in [COLOR_RGBALPHA] then
begin
AlphaRowT := PNGOriginal.AlphaScanline[ Oht ];
AlphaStartPtr := PNGOriginal.AlphaScanline[ 0 ];
AlphaRotatedT := wPng.AlphaScanline[ Rht ];
AlphaSizeRot := Integer(wPng.AlphaScanline[1])-Integer(wPng.AlphaScanline[0]);
AlphaSizeOrg := Integer(PNGOriginal.AlphaScanline[1])-Integer(PNGOriginal.AlphaScanline[0]);
end
else
begin
AlphaRowT := nil;
AlphaStartPtr := nil;
AlphaRotatedT := nil;
AlphaSizeRot := 0;
AlphaSizeOrg := 0;
end;
for j := Rht downto 0 DO //1/8/00
begin //for j
jPrime := 2*j - NewHeight + 1 ;
for i := Rwi downto 0 DO //1/8/00
begin //for i
iPrime := 2*i - NewWidth + 1;
iOriginal := ( ROUND( iPrime*CosTheta - jPrime*sinTheta ) + Owi ) div 2;
if ( iOriginal >= 0 ) and ( iOriginal <= Owi ) then
begin //inside
jOriginal := ( ROUND( iPrime*sinTheta + jPrime*cosTheta ) + Oht ) div 2 ;
if ( jOriginal >= 0 ) and ( jOriginal <= Oht ) then
begin //1/8/00
RowRotatedT[i] := pRGBTripleArray(Integer(RowStartPtr) + (jOriginal * RowSizeOrg))[iOriginal];
if assigned(AlphaRotatedT) then
AlphaRotatedT[i] := pByteArray(Integer(AlphaStartPtr) + (jOriginal * AlphaSizeOrg))[iOriginal];
end
else
begin //set Transparent
if Assigned(AlphaRotatedT) then
AlphaRotatedT[i] := 0;
RowRotatedT[i] := TransparentT;
end;
end //inside
else
begin //Set Transpaarent;
if Assigned(AlphaRotatedT) then
AlphaRotatedT[i] := 0;
RowRotatedT[i] := TransparentT;
end;
end; //for i
Dec(Integer(RowRotatedT), RowSizeRot) ;
if assigned(AlphaRotatedT) then
Dec(Integer(AlphaRotatedT), AlphaSizeRot) ;
end;//for j
PNGRotated.Assign(wPng);
finally
wPng.Free;
end;
end //non-zero rotation
else
begin //Zero rotation
if PNGRotated <> PNGOriginal then
PNGRotated.Assign(PNGOriginal);
end;
end; {RotatePNG}