Class TEncodedImage

Unit

Declaration

type TEncodedImage = class(TObject)

Description

Abstract class for an image with unspecified, possibly compressed, memory format. The idea is that both uncompressed images (TCastleImage) and images compressed for GPU (TGPUCompressedImage) are derived from this class.

Hierarchy

  • TObject
  • TEncodedImage

Overview

Fields

Protected FRawPixels: Pointer;

Methods

Public destructor Destroy; override;
Public function Size: Cardinal; virtual; abstract;
Public function Dimensions: TVector3Cardinal;
Public function IsEmpty: boolean;
Public function HasAlpha: boolean; virtual;
Public function AlphaChannel( const AlphaTolerance: Byte = DefaultAlphaTolerance): TAlphaChannel; virtual;
Public function Rect: TRectangle;
Public function CreateCopy: TEncodedImage; virtual; abstract;

Properties

Public property URL: string read FURL write FURL;
Public property Width: Cardinal read FWidth;
Public property Height: Cardinal read FHeight;
Public property Depth: Cardinal read FDepth;
Public property RawPixels: Pointer read FRawPixels;

Description

Fields

Protected FRawPixels: Pointer;

Operate on this by Get/Realloc/FreeMem. It's always freed and nil'ed in destructor.

Methods

Public destructor Destroy; override;
 
Public function Size: Cardinal; virtual; abstract;

Size of image contents in bytes.

Public function Dimensions: TVector3Cardinal;
 
Public function IsEmpty: boolean;

Is an image empty.

True means that RawPixels = Nil, and Width * Height * Depth = 0 (so either Width = 0 or Height = 0 or Depth = 0).

False means that RawPixels <> nil and Width * Height * Depth <> 0 (so all Width > 0 and Height > 0 and Depth > 0, since they are Cardinal (unsigned) always).

Public function HasAlpha: boolean; virtual;

Does an image have an alpha channel.

You may also be interested in the AlphaChannel. AlphaChannel answers always atNone if HasAlpha = false, and always acTest or acBlending if HasAlpha = true. But AlphaChannel may perform longer analysis of pixels (to differ between acTest and acBlending), while this function always executes ultra-fast (as it's constant for each TCastleImage descendant).

Descendants implementors notes: in this class, TCastleImage, this returns False. Override to return True for images with alpha channel.

Public function AlphaChannel( const AlphaTolerance: Byte = DefaultAlphaTolerance): TAlphaChannel; virtual;

Check does an image have an alpha channel, and if yes analyze alpha channel: is it a single yes-no (only full or none values), or does it have alpha values in between?

This is quite useful for automatic detection how alpha textures should be displayed: for simple yes/no alpha, OpenGL alpha_test is a simple solution. For full range alpha, OpenGL blending should be used. Blending is a little problematic, since it requires special rendering order, since it doesn't cooperate nicely with Z-buffer. That's why we try to detect simple yes/no alpha textures, so that we're able to use simpler alpha test for them.

We return "simple yes/no alpha channel" is all the alpha values (for every pixel) are 0, or 255, or (when AlphaTolerance <> 0) are close to them by AlphaTolerance. So, to be precise, alpha value must be <= AlphaTolerance, or >= 255 - AlphaTolerance. If any alpha value is between [AlphaTolerance + 1, 255 - AlphaTolerance - 1] then we return "full range alpha channel". Note that for AlphaTolerance >= 128, all images are treated as "simple yes/no alpha". Usually, you want to keep AlphaTolerance small.

Descendants implementors notes: in this class, this simply always returns atNone. For descendants that have alpha channel, implement it, honouring AlphaTolerance as described.

Public function Rect: TRectangle;

Rectangle representing the inside of this image. Always (Left,Bottom) are zero, and (Width,Height) correspond to image sizes.

Public function CreateCopy: TEncodedImage; virtual; abstract;

Create a new image object that has exactly the same class and the same data (size, pixels) as this image.

Properties

Public property URL: string read FURL write FURL;

URL from which this image was loaded, if any.

Public property Width: Cardinal read FWidth;
 
Public property Height: Cardinal read FHeight;
 
Public property Depth: Cardinal read FDepth;
 
Public property RawPixels: Pointer read FRawPixels;
 

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