Image formats in general
The Graphics32 library only supports BMP files natively. Alternatively files can be handled using TBitmap internally and thus loading of all supported TBitmap file formats such as JPG, GIF and PNG is possible using the VCL. However, since reading and writing utilizes an intermediate TBitmap object, unnecessary additional memory is required to store the bitmap data. Also by converting data to and from the TBitmap format additional information might get lost or handled wrong.
1. I can not load JPEG images at run-time, but at design-time this does work. What's wrong?
Include JPEG unit into the uses clause in your main application unit.
2. Is there a PNG library for GR32 which supports loading the image and its alpha channel at the same time?
To handle PNG files natively by Graphics32 the thirdparty library GR32 PNG Library can be used. This library use the native PNG format as intermediate storage. By assigning a TBitmap32 object the data is encoded/decoded to/from PNG on the fly. Using this library it is also possible to access additional information, which is stored in the PNG file. It's also possible to transcode the data to different encodings.
3. I want to support as much other file formats as possible! What options do I have?
You might want to take a look at GraphicEx. It loads several different file formats, but only write a few of them. For example loading PNGs with alpha channel is supported out of the box, but the PNG support in GraphicEx is very basic and there is no way to save back to PNG (see 3). for more information on how to load PNG files).
Alternatively it is possible to load other file formats using GDI+.
4. What's up with the TPNGImage library?
In the past a library for handling PNG files was available called PNGImage (using a TPNGImage/TPNGObject). It was brought by Embarcadero and is now part of Delphi. The original open source project has been shut down. Since it is based on a TBitmap, it can be used with Graphics32, but doesn't handle transparency out of the box.
Due to this reason is not recommended to use this library in the first place (see 2). However, if required you can use the following code:
unit GR32_PNG; interface uses SysUtils, Windows, Classes, GR32, Graphics; procedure LoadPNGintoBitmap32(DstBitmap: TBitmap32; Filename: String; out AlphaChannelUsed: Boolean); overload; procedure LoadPNGintoBitmap32(DstBitmap: TBitmap32; SrcStream: TStream; out AlphaChannelUsed: Boolean); overload; implementation uses PNGImage; procedure LoadPNGintoBitmap32(DstBitmap: TBitmap32; SrcStream: TStream; out AlphaChannelUsed: Boolean); var PNGObject: TPNGObject; TransparentColor: TColor32; PixelPtr: PColor32; AlphaPtr: PByte; X, Y: Integer; begin PNGObject := nil; try PNGObject := TPngObject.Create; PNGObject.LoadFromStream(SrcStream); DstBitmap.Assign(PNGObject); DstBitmap.ResetAlpha; case PNGObject.TransparencyMode of ptmPartial: begin if (PNGObject.Header.ColorType = COLOR_GRAYSCALEALPHA) or (PNGObject.Header.ColorType = COLOR_RGBALPHA) then begin PixelPtr := PColor32(@DstBitmap.Bits); for Y := 0 to DstBitmap.Height - 1 do begin AlphaPtr := PByte(PNGObject.AlphaScanline[Y]); for X := 0 to DstBitmap.Width - 1 do begin PixelPtr^ := (PixelPtr^ and $00FFFFFF) or (TColor32(AlphaPtr^) shl 24); Inc(PixelPtr); Inc(AlphaPtr); end; end; AlphaChannelUsed := True; end; end; ptmBit: begin TransparentColor := Color32(PNGObject.TransparentColor); PixelPtr := PColor32(@DstBitmap.Bits); for X := 0 to DstBitmap.Height * DstBitmap.Width - 1 do begin if PixelPtr^ = TransparentColor then PixelPtr^ := PixelPtr^ and $00FFFFFF; Inc(PixelPtr); end; AlphaChannelUsed := True; end; ptmNone: AlphaChannelUsed := False; end; finally if Assigned(PNGObject) then PNGObject.Free; end; end; procedure LoadPNGintoBitmap32(DstBitmap: TBitmap32; Filename: String; out AlphaChannelUsed: Boolean); var FileStream: TFileStream; begin FileStream := TFileStream.Create(Filename, fmOpenRead); try LoadPNGintoBitmap32(DstBitmap, FileStream, AlphaChannelUsed); finally FileStream.Free; end; end; end.
Code usage example:
var AlphaChannelUsed: Boolean begin LoadPNGintoBitmap32(MyBitmap, 'someimage.png', AlphaChannelUsed); if AlphaChannelUsed then // add anything else that should be done if we have // an alpha channel with our PNG image... MyBitmap.DrawMode := dmBlend else MyBitmap.DrawMode := dmOpaque; end;