8.12.3.22 IfcPixelTexture

8.12.3.22.1 Semantic definition

An IfcPixelTexture provides a 2D image-based texture map as an explicit array of pixel values (list of Pixel binary attributes). In contrary to the IfcImageTexture the IfcPixelTexture holds a 2 dimensional list of pixel color (and opacity) directly, instead of referencing to an URL.

The following definitions from ISO/IEC 19775-1 X3D Architecture and base components (X3D Specification) apply:

The PixelTexture node defines a 2D image-based texture map as an explicit array of pixel values (image field) and parameters controlling tiling repetition of the texture onto geometry.
Texture maps are defined in a 2D coordinate system (s, t) that ranges from 0.0 to 1.0 in both directions. The bottom edge of the pixel image corresponds to the S-axis of the texture map, and left edge of the pixel image corresponds to the T-axis of the texture map. The lower-left pixel of the pixel image corresponds to s=0.0, t=0.0, and the top-right pixel of the image corresponds to s = 1.0, t = 1.0.
The Image field specifies a single uncompressed 2-dimensional pixel image. Image fields contain three integers representing the width, height and number of components in the image, followed by width×height hexadecimal values representing the pixels in the image. Pixel values are limited to 256 levels of intensity (that is, 0x00-0xFF hexadecimal).
A one-component image specifies one-byte hexadecimal value representing the intensity of the image. For example, 0xFF is full intensity in hexadecimal (255 in decimal), 0x00 is no intensity (0 in decimal).
A two-component image specifies the intensity in the first (high) byte and the alpha opacity in the second (low) byte.
Pixels in a three-component image specify the red component in the first (high) byte, followed by the green and blue components (for example, 0xFF0000 is red, 0x00FF00 is green, 0x0000FF is blue).
Four-component images specify the alpha opacity byte after red/green/blue (e.g., 0x0000FF80 is semi-transparent blue). A value of 00 is completely transparent, FF is completely opaque, 80 is semi-transparent.
Note that alpha equals (1.0 -transparency), if alpha and transparency each range from 0.0 to 1.0.

8.12.3.22.2 Entity inheritance

8.12.3.22.3 Attributes

#	Attribute	Type	Description
IfcSurfaceTexture (7)
1	RepeatS	IfcBoolean	The RepeatS field specifies how the texture wraps in the S direction. If RepeatS is TRUE (the default), the texture map is repeated outside the [0.0, 1.0] texture coordinate range in the S direction so that it fills the shape. If RepeatS is FALSE, the texture coordinates are clamped in the S direction to lie within the [0.0, 1.0] range.
2	RepeatT	IfcBoolean	The RepeatT field specifies how the texture wraps in the T direction. If RepeatT is TRUE (the default), the texture map is repeated outside the [0.0, 1.0] texture coordinate range in the T direction so that it fills the shape. If RepeatT is FALSE, the texture coordinates are clamped in the T direction to lie within the [0.0, 1.0] range.
3	Mode	OPTIONAL IfcIdentifier	Mode shall hold the type of map this corresponds to, chosen from the following list: AMBIENT, NORMAL, EMISSIVE, METALLICROUGHNESS, OCCLUSION, SHININESS, SPECULAR, DIFFUSE. If Mode is omitted, DIFFUSE is assumed. IFC4-CHANGE New attribute replacing previous TextureType. IFC4.3.0.0-CHANGE Attribute has been repurposed to store the type of texture.
4	TextureTransform	OPTIONAL IfcCartesianTransformationOperator2D	The TextureTransform defines a 2D transformation that is applied to the texture coordinates. It affects the way texture coordinates are applied to the surfaces of geometric representation items. The 2D transformation supports changes to the size, orientation, and position of textures on shapes. Mirroring is not allowed to be used in the IfcCartesianTransformationOperator
5	Parameter	OPTIONAL LIST [1:?] OF IfcIdentifier	IFC4.3.0.0-DEPRECATION This attribute is deprecated and shall no longer be used.
	IsMappedBy	SET [0:?] OF IfcTextureCoordinate FOR Maps	Texture coordinates, either provided by a corresponding list of texture vertices to vertex-based geometric items or by a texture coordinate generator, that applies the surface texture to the surfaces of the geometric items. IFC4-CHANGE New attribute added at the end of the attribute list.
	UsedInStyles	SET [0:?] OF IfcSurfaceStyleWithTextures FOR Textures	No description available.
Click to show 7 hidden inherited attributes
IfcPixelTexture (4)
6	Width	IfcInteger	The number of pixels in width (S) direction.
7	Height	IfcInteger	The number of pixels in height (T) direction.
8	ColourComponents	IfcInteger	Indication whether the pixel values contain a 1, 2, 3, or 4 colour component.
9	Pixel	LIST [1:?] OF IfcBinary	Flat list of hexadecimal values, each describing one pixel by 1, 2, 3, or 4 components. IFC2x3-CHANGE The data type has been changed from STRING to BINARY.

Table 8.12.3.22.B

8.12.3.22.4 Formal propositions

Name Description

MinPixelInS

The minimum number of pixel in width (S coordinate) direction shall be 1.

Width >= 1

MinPixelInT

The minimum number of pixel in height (T coordinate) direction shall be 1.

Height >= 1

NumberOfColours

The number of color components shall be either 1, 2, 3, or 4.

{1 <= ColourComponents <= 4}

PixelAsByteAndSameLength

The binary value provided for each Pixel shall be a multiple of 8 bits. And all pixel shall have the same binary length.

 SIZEOF(QUERY(temp<* Pixel |
 (BLENGTH(temp) MOD 8 = 0) AND
 (BLENGTH(temp) = BLENGTH(Pixel[1]))
)) = SIZEOF(Pixel)

SizeOfPixelList

The list of pixel shall have exactly width*height members.

SIZEOF(Pixel) = (Width * Height)

Table 8.12.3.22.C

8.12.3.22.5 Examples

Figure 8.12.3.22.A

Tessellation With Pixel Texture

8.12.3.22.6 Formal representation

 ENTITY IfcPixelTexture
 SUBTYPE OF (IfcSurfaceTexture);
	Width : IfcInteger;
	Height : IfcInteger;
	ColourComponents : IfcInteger;
	Pixel : LIST [1:?] OF IfcBinary;
 WHERE
	MinPixelInS : Width >= 1;
	MinPixelInT : Height >= 1;
	NumberOfColours : {1 <= ColourComponents <= 4};
	PixelAsByteAndSameLength : SIZEOF(QUERY(temp<* Pixel |
 (BLENGTH(temp) MOD 8 = 0) AND
 (BLENGTH(temp) = BLENGTH(Pixel[1]))
)) = SIZEOF(Pixel);
	SizeOfPixelList : SIZEOF(Pixel) = (Width * Height);
END_ENTITY;

8.12.3.22.7 References

IfcSurfaceTexture