OpenVG1.1lite - CSDN文库

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OpenVG（Open Vector Graphics）是一种用于硬件加速2D矢量图形的API，由Khronos Group制定并维护。OpenVG1.1 Lite是OpenVG的最新版本，于2020年5月29日发布（版本A005）。该规范经过多年的更新完善，旨在为开发人员提供更加强大和高效的图形渲染能力。 OpenVG1.1 Lite规范的编辑者包括来自Ajou大学的Hwanyong Lee，Qualcomm的Robert J. Simpson以及Google公司的Daniel Rice。他们共同工作，致力于不断优化和提高OpenVG的性能和功能，以满足不断发展的行业需求。在历经数个版本的更新后，OpenVG1.1 Lite在功能和性能上均得到了显著的提升。通过不断更新的OpenVG1.1 Lite规范，开发人员可以更加方便地利用硬件加速技术实现高质量的2D矢量图形渲染。OpenVG1.1 Lite支持包括路径绘制、颜色填充、图案填充、渐变填充等多种图形绘制和渲染操作，同时还提供了对图像合成、滤镜效果、图像变换等功能的全面支持。得益于OpenVG1.1 Lite规范的不断完善，开发人员能够更轻松地实现复杂的图形渲染效果，为用户呈现出更加真实、精美的视觉体验。在智能手机、平板电脑、汽车信息娱乐系统以及其他嵌入式系统中，OpenVG1.1 Lite可以发挥其强大的图形渲染能力，为用户带来更加流畅和生动的用户界面和交互体验。同时，OpenVG1.1 Lite规范还支持对图形接口的3D图形渲染API进行衔接，使得开发人员可以更加灵活地实现2D和3D图形的混合渲染，为用户带来更加丰富和多样的视觉效果。这使得OpenVG1.1 Lite成为了嵌入式系统和移动设备领域中不可或缺的图形渲染技术之一。总之，OpenVG1.1 Lite规范作为硬件加速2D矢量图形渲染API的最新版本，为开发人员提供了更加强大和高效的图形渲染能力。通过对图形绘制、渲染和效果处理等方面的全面支持，OpenVG1.1 Lite可以满足不同领域的图形渲染需求，为用户带来更加流畅、生动和丰富的视觉体验。随着技术的不断进步和行业需求的不断变化，OpenVG1.1 Lite规范也将持续不断地完善和发展，为开发人员提供更加强大和全面的图形渲染解决方案。

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be represented by a VGshort is given by (– VG_MAXSHORT – 1), or -32,768.

VG_MAXINT

The macro VG_MAXINT contains the largest positive value that may be represented by a VGint. VG_MAXINT

is defined to be equal to 2

– 1, or 2,147,483,647. The smallest negative value that may be represented

by a VGint is given by ( –VG_MAXINT – 1), or -2,147,483,648.

VG_MAX_FLOAT

The parameter VG_MAX_FLOAT contains the largest floating-point number that will be accepted by an

implementation. To query the parameter, use the vgGetf function with a paramType argument of

VG_MAX_FLOAT (see Section 5.2). All implementations must define VG_MAX_FLOAT to be at least 10

3.4 Colors

Colors in OpenVG Lite other than those stored in image pixels (e.g., colors for clearing, painting, and

edge extension for convolution) are represented as non-premultiplied (see Section 3.4.3) sRGBA

[sRGB99] color values. Image pixels may be defined in a number of color spaces, including sRGB, linear

RGB, linear grayscale (or luminance) and nonlinearly coded, perceptually-uniform grayscale, in

premultiplied or non-premultiplied form. Color and alpha values lie in the range [0,1] unless otherwise

noted. This applies to intermediate values in the pixel pipeline as well as to application-specified values. If

an alpha channel is present but has a bit depth of zero, the alpha value of each pixel is taken to be 1.

Non-linear quantities are denoted using primed (’) symbols below. [POYN03] contains an excellent

discussion of the use of non-linear coding to achieve perceptual uniformity.

3.4.1 Linear and Non-Linear Color Representations

OpenVG Lite use linear RGBA color in processing. Therefore, if user want display rendering result with

sRGB format, user should add conversion process for input or output color data in his application. It may

be executed in OpenVG Lite or EGL. In a linear color representation, the numeric values associated with

a color channelvalue measure the rate at which light is emitted by an object, multiplied by someconstant

scale factor. Informally, it can be thought of as counting the number of photonsemitted in a given amount

of time. Linear representations are useful for computation,since light values may be added together in a

physically meaningful way.

However, the human visual system responds non-linearly to the light power ("intensity") of an image.

Accordingly, many common image coding standards (e.g., the EXIF JPEG format used by many digital

still cameras and the MPEG format used for video) utilize non-linear relationships between light power

and code values. This allows a larger number of distinguishable colors to be represented in a given

number of bits than is possible with a linear encoding. Common display devices such as CRTs and LCDs

also emit light whose power at each pixel component is proportional to a non-linear power function (i.e., a

function of the form xa where a is constant) of the applied code value, whether due to the properties of

analog CRT electronics or to the deliberate application of a non-linear transfer function elsewhere in the

signal path. The exponent, or gamma, of this power function is typically between 2.2 and 2.5. OpenVG

makes use of the nonlinear sRGB color specification described below.

Because linear coding of intensity fails to optimize the number of distinguishablevalues, 8-bit linear pixel

formats suffer from poor contrast ratios and banding artifacts; their use with photographic imagery is not

recommended. However, synthetic imagery generated by other APIs such as OpenGL ES that make use

of linear light may require the use of linear formats. 8-bit linear coding is also appropriate for representing

pseudoimages such as coverage masks that are not based on perceptual light intensity.

Although computing directly with non-linear representations may lead to significant errors compared with

the results of first converting to a linear representation, it is common industry practice in many imaging

domains to do so. Because the cost of performing linearization on pixel values to be interpolated or

blended is considered prohibitive for mobile devices in the near future, OpenVG may perform these

operations directly on non-linear code values. A future version of this specification may introduce flags to

force values to be converted to a linear representat***

3.4.2 Color Space Definitions

The linear lRGB color space is defined in terms of the standard CIE XYZ color space [WYSZ00], following

ITU Rec. 709 [ITU90] using a D65 white point:

The sRGB color space defines values , , in terms of the linear lRGB primaries by

applying a gamma ( ) mapping consisting of a linear segment and an offset power function:

The inverse mapping is defined as:

To convert from lRGB to sRGB, the gamma mapping is used:

To convert from sRGB to lRGB, the inverse gamma mapping is used:

R = 3.240479X − 1.537150Y –0.498535Z

G = −0.969256X + 1.875992Y + 0.041556Z

B = 0.055648X–0.204043Y + 1.057311Z

sRGB

′

sRGB

′

sRGB

′

if x ≤ 0.00304

γ(x) = 12.92x

else

γ(x) = 1.0556x −

1/2.4

0.0556

−1

if x ≤ 0.03928

γ (x) =

−1

x/12.92

else

γ (x) =

−1

[(x + 0.0556)/1.0556]

2.4

R =

sRGB

′

γ(R)

G =

sRGB

′

γ(G)

B =

sRGB

′

γ(B) (1)

R = γ (R )

−1

sRGB

′

If the source and destination color formats are of differing color spaces (i.e., linear RGB, sRGB, linear

grayscale, perceptually-uniform grayscale), each source channel is divided by the maximum channel

value to produce a number between 0 and 1. The color space conversion is performed as described

above. The resulting values are then scaled by the maximum value for each destination channel.

If the source and destination formats have the same color format, but differ in the number of bits per color

channel, the source value is multiplied by the quotient (where is the number of bits in

the destination and is the number of bits in the source) and rounded to the nearest integer.

The following approximation may be used in place of exact multiplication: If the source channel has a

greater number of bits than the destination, the most significant bits are preserved and the least

significant bits are discarded. If the source channel has a lesser number of bits than the destination, the

value is shifted left and the most significant bits are replicated in the less significant bit positions. For

example, a 5-bit source value will be converted to an 8-bit destination value

. This rule approximates the correct result since if for some integer k > 1 the

quotient will be an integer of the form , and

multiplication of an s-bit value by this value will be exactly equivalent to bit replication. When the

destination bit depth is not an integer multiple of the source bit depth, this rule still provides greater

accuracy than other possible approximations such as padding the source with zeros or with copies of the

rightmost bit.

Note that converting from a lesser to a greater number of bits and back again using either exact scaling

or the approximation will result in an unchanged value. If the destination format has stored alpha, the

previously saved alpha value is stored into the destination. If the destination format has premultiplied

alpha, each color channel value is multiplied by the corresponding alpha value and the resulting values

are clamped to the range [0, alpha].

3.5 Enumerated Data Types

A number of data types are defined using the C enum keyword. In all cases, this specification assigns

each enumerated constant a particular integer value. Extensions to the specification wishing to add new

enumerated values must register with the Khronos Group to receive a unique value (see Section 15).

Applications making use of extensions should cast the extension-defined integer value to the proper

enumerated type.

The enumerated types (apart from VGboolean ) defined by OpenVG Lite are:

VGBlendMode

VGCapStyle

VGColorRampSpreadMode

VGErrorCode

VGFillRule

VGFontParamType

VGHardwareQueryResult

VGHardwareQueryType

(2 –1)/(2 –1)

d s

b b b b b

4 3 2 1 0

b b b b b b b b

4 3 2 1 0 4 3 2

d = k ∗ s

(2 –1)/(2 –1)

d s

2 +

(k−1)s

2 +

(k−2)s

... + 2 +

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