Graphics32

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Loading, Saving & Image Formats ​

Graphics32 supports loading and saving 32-bit images across common graphics formats including PNG, JPEG, BMP, and Photoshop PSD files.

In this tutorial, you will learn how to load images from disk files and in-memory streams, preserve alpha transparency, and exchange bitmaps with standard VCL / Lazarus components (TBitmap, TPicture, TImage).

1. File I/O with LoadFromFile and SaveToFile ​

TBitmap32 includes LoadFromFile and SaveToFile methods. Graphics32 automatically registers image format adapters based on file extensions.

pascal
uses
  Classes, SysUtils, 
  GR32, 
  GR32.ImageFormats.PNG32; // Include GR32.ImageFormats.PNG32 for native PNG support

procedure LoadAndSaveExample;
var
  Bitmap: TBitmap32;
begin
  Bitmap := TBitmap32.Create;
  try
    // 1. Load 32-bit PNG image with alpha channel
    Bitmap.LoadFromFile('input_transparent.png');

    // Inspect loaded dimensions
    Writeln(Format('Loaded image dimensions: %dx%d', [Bitmap.Width, Bitmap.Height]));

    // Perform drawing modifications...
    Bitmap.FillRectTS(10, 10, 100, 100, clTrRed32);

    // 2. Save result as PNG preserving full alpha transparency
    Bitmap.SaveToFile('output_modified.png');

    // 3. Save result as standard BMP
    Bitmap.SaveToFile('output_backup.bmp');
  finally
    Bitmap.Free;
  end;
end;

2. Working with In-Memory Streams ​

When dealing with database BLOBs, network downloads, or embedded binary assets, you can load and save directly from TStream instances using LoadFromStream and SaveToStream.

pascal
procedure LoadBitmapFromStream(Stream: TStream; TargetBitmap: TBitmap32);
begin
  Stream.Position := 0;

  // Load stream content into TBitmap32
  TargetBitmap.LoadFromStream(Stream);
end;

procedure SaveBitmapToStream(SourceBitmap: TBitmap32; Stream: TStream);
begin
  // Save as BMP stream
  SourceBitmap.SaveToStream(Stream);
end;

INFO

When loading from a file Graphics32 will use both the file type and the content of the file to determine the image format. When loading from a stream it will of course only use the content.

When saving to a file it will use the file type to determine the target image format, and if that fails, it will fall back to BMP. When saving to a stream it will always save as BMP.

3. Converting Between Standard VCL/FCL TBitmap and TBitmap32 ​

In Delphi and Lazarus applications, you frequently need to exchange image data between standard VCL/FCL controls (TImage, TPicture, Graphics.TBitmap) and TBitmap32.

TBitmap32 supports the standard Assign/AssignTo pattern for easy conversion to and from all TGraphic-based image formats.

Converting VCL TBitmap -> TBitmap32 ​

pascal
uses
  Graphics, GR32;

procedure ConvertVclToGR32(SourceBitmap: Graphics.TBitmap; DestBitmap: TBitmap32);
begin
  // Assign handles color conversion and pixel copy automatically
  //
  // Graphics32 takes care of setting the alpha channel to 
  // opaque ($FF) if the source bitmap lacked alpha.
  DestBitmap.Assign(SourceBitmap);
end;

Converting TBitmap32 -> VCL TBitmap ​

pascal
procedure ConvertGR32ToVcl(SourceBitmap: TBitmap32; DestBitmap: Graphics.TBitmap);
begin
  // Assign copies pixels from TBitmap32 into standard VCL TBitmap
  DestBitmap.Assign(SourceBitmap);
end;

INFO

The Assign/AssignTo pattern simply means that both the source and the destination get a chance at performing the conversion; First the destination (Dest.Assign(Source)) and then the source (Source.AssignTo(Dest)).

As a result it is possible to perform a conversion if just one of the participants knows how to do it.

In the case of a conversion to TBitmap32 where neither parts can handle the conversion, Graphics32 falls back to simply drawing the source on the destination bitmap.

Summary ​

In this tutorial, you learned:

  1. How to load and save PNG, JPEG, and BMP files using LoadFromFile and SaveToFile.
  2. How to process image data in memory streams using LoadFromStream and SaveToStream.
  3. How to convert pixels between VCL/FCL TBitmap and Graphics32 TBitmap32 using Assign.

Next, proceed to Repaint Optimization & Custom Canvas Drawing to learn how to paint efficiently without flickering!