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樱花视频高清 - Raw

KHR_lights_punctual

Contributors

Copyright 2017-2018 The Khronos Group Inc. All Rights Reserved. glTF is a trademark of The Khronos Group Inc. See Appendix for full Khronos Copyright Statement.

Status (樱花视频高清)

Complete, Ratified by the Khronos Group

Dependencies

Written against the glTF 2.0 spec.

Overview

樱花视频免费观看.

Many 3D tools and engines support built-in implementations of light types 樱花视频网站. Using this extension, tools can export and engines can import these lights.

This extension defines three "punctual" light types: directional, point and spot. Punctual lights are defined as parameterized, infinitely small points that emit light in well-defined directions and intensities 樱花视频.

These lights are referenced by nodes and inherit the transform of that node.

A conforming implementation of this extension must be able to load light data defined in the asset and has to render the asset using those lights.

Defining Lights

extensions property to the top-level glTF 2 樱花视频免费观看. 0 object and defining a KHR_lights_punctual property with a lights array inside it.

Each light defines a mandatory type property that designates the type of light (directional, point or spot) 樱花视频网站. The following example defines a white-colored directional light.

"extensions": {
    "KHR_lights_punctual" : {
        "lights": [
            {
                "color": [
                    1.0,
                    1.0,
                    1.0
                ],
                "type": "directional"
            }
        ]
    }
}

Adding Light Instances to Nodes

Lights must be attached to a node by defining the extensions.KHR_lights_punctual property and, within that, an index into the lights array using the light property.

"nodes" : [
    {
        "extensions" : {
            "KHR_lights_punctual" : {
                "light" : 0
            }
        }
    }
]

The light will inherit the transform of the node. For light types that have a position (point and spot lights), the light's position is defined as the node's world location. For light types that have a direction (directional and spot lights), the light's direction is defined as the 3-vector (0.0, 0.0, -1.0) and the rotation of the node orients the light accordingly. That is, an untransformed light points down the -Z axis. The light's transform is affected by the node's world scale, but all properties of the light (such as range and intensity) are unaffected 樱花视频在线.

Light Types

Light Shared Properties

All light types share the common set of properties listed below.

PropertyDescriptionRequired
nameName of the light.No, Default: ""
colorRGB value for the light's color in linear space.No, Default: [1.0, 1.0, 1.0]
intensityBrightness of the light. The units that this is defined in depend on the type of light. point and spot lights use luminous intensity in candela (lm/sr) while directional lights use illuminance in lux (lm/m2)No, Default: 1.0
typeDeclares the type of the light.✅ Yes
rangeHint defining a distance cutoff at which the light's intensity may be considered to have reached zero. Supported only for point and spot lights. Must be> 0. When undefined, range is assumed to be infinite.No

Light properties are unaffected by node transforms — for example, range and intensity do not change with scale.

The intensity represents the luminous intensity that the light would emit if it were colored pure white ([1.0, 1.0, 1.0]). The color property acts as a wavelength-specific multiplier 樱花视频网站.

Range Property

樱花视频. It is required that, when given a non-zero value, rendering engines ignore the light beyond this range.

Within the range of the light, attenuation should follow the inverse square law as closely as possible, although some non-quadratic falloff near the edge of the range may be used to avoid a hard cutoff. When undefined, range is assumed to be infinite and the light should attenuate according to inverse square law 樱花视频在线.

A recommended implementation for this attenuation with a cutoff range is as follows:

attenuation = max( min( 1.0 - ( current_distance / range )4, 1 ), 0 ) / current_distance2

Directional

Directional lights are light sources that act as though they are infinitely far away and emit light in the direction of the local -z axis. This light type inherits the orientation of the node that it belongs to; position and scale are ignored except for their effect on the inherited node orientation. Because it is at an infinite distance, the light is not attenuated. Directional light intensity is defined in lumens per metre squared, or lux (lm/m2).

Point (樱花视频网站)

Point lights emit light in all directions from their position in space; rotation and scale are ignored except for their effect on the inherited node position. The brightness of the light attenuates in a physically correct manner as distance increases from the light's position (i.e. brightness goes like the inverse square of the distance). Point light intensity is defined in candela, which is lumens per square radian (lm/sr).

樱花视频网站 - Spot

Spot lights emit light in a cone in the direction of the local -z axis. The angle and falloff of the cone is defined using two numbers, the innerConeAngle and outerConeAngle. As with point lights, the brightness also attenuates in a physically correct manner as distance increases from the light's position (i.e. brightness goes like the inverse square of the distance). Spot light intensity refers to the brightness inside the innerConeAngle (and at the location of the light) and is defined in candela, which is lumens per square radian (lm/sr). Engines that don't support two angles for spotlights should use outerConeAngle as the spotlight angle (leaving innerConeAngle to implicitly be 0).

A spot light's position and orientation are inherited from its node transform. Inherited scale does not affect cone shape, and is ignored except for its effect on position and orientation.

When a light's type is spot, the spot property on the light is required. Its properties (below) are optional.

PropertyDescriptionRequired
innerConeAngleAngle, in radians, from centre of spotlight where falloff begins. Must be greater than or equal to 0 and less than outerConeAngle.No, Default: 0
outerConeAngleAngle, in radians, from centre of spotlight where falloff ends. Must be greater than innerConeAngle and less than or equal to PI / 2.0.No, Default: PI / 4.0
"extensions": {
    "KHR_lights_punctual" : {
        "lights": [
            {
                "spot": {
                    "innerConeAngle": 0.785398163397448,
                    "outerConeAngle": 1.57079632679,
                },
                "color": [
                    1.0,
                    1.0,
                    1.0
                ],
                "type": "spot"
            }
        ]
    }
}

Inner and Outer Cone Angles

There should be a smooth attenuation of brightness between the innerConeAngle and outerConeAngle angles. In reality, this "angular" attenuation is very complex as it depends on the physical size of the spotlight and the shape of the sheath around the bulb.

Conforming implementations will model this angular attenuation with a curve that follows a steeper decline in brightness before leveling off when moving from the inner to the outer angle.

It is common to model this falloff by interpolating between the cosine of each angle. This is an efficient approximation that provides decent results.

Reference code:

// These two values can be calculated on the CPU and passed into the shader
float lightAngleScale = 1.0f / max(0.001f, cos(innerConeAngle) - cos(outerConeAngle));
float lightAngleOffset = -cos(outerConeAngle) * lightAngleScale;

// Then, in the shader:
float cd = dot(spotlightDir, normalizedLightVector);
float angularAttenuation = saturate(cd * lightAngleScale + lightAngleOffset);
angularAttenuation *= angularAttenuation;

樱花视频 - Appendix: Full Khronos Copyright Statement

Copyright 2017-2018 The Khronos Group Inc.

Some parts of this Specification are purely informative and do not define requirements necessary for compliance and so are outside the Scope of this Specification. These parts of the Specification are marked as being non-normative, or identified as Implementation Notes.

Where this Specification includes normative references to external documents, only the specifically identified sections and functionality of those external documents are in Scope. Requirements defined by external documents not created by Khronos may contain contributions from non-members of Khronos not covered by the Khronos Intellectual Property Rights Policy.

This specification is protected by copyright laws and contains material proprietary to Khronos. Except as described by these terms, it or any components may not be reproduced, republished, distributed, transmitted, displayed, broadcast or otherwise exploited in any manner without the express prior written permission of Khronos.

This specification has been created under the Khronos Intellectual Property Rights Policy, which is Attachment A of the Khronos Group Membership Agreement available at www.khronos.org/files/member_agreement.pdf. Khronos grants a conditional copyright license to use and reproduce the unmodified specification for any purpose, without fee or royalty, EXCEPT no licenses to any patent, trademark or other intellectual property rights are granted under these terms. Parties desiring to implement the specification and make use of Khronos trademarks in relation to that implementation, and receive reciprocal patent license protection under the Khronos IP Policy must become Adopters and confirm the implementation as conformant under the process defined by Khronos for this specification; see https://www.khronos.org/adopters.

Khronos makes no, and expressly disclaims any, representations or warranties, express or implied, regarding this specification, including, without limitation: merchantability, fitness for a particular purpose, non-infringement of any intellectual property, correctness, accuracy, completeness, timeliness, and reliability. Under no circumstances will Khronos, or any of its Promoters, Contributors or Members, or their respective partners, officers, directors, employees, agents or representatives be liable for any damages, whether direct, indirect, special or consequential damages for lost revenues, lost profits, or otherwise, arising from or in connection with these materials.

Vulkan is a registered trademark and Khronos, OpenXR, SPIR, SPIR-V, SYCL, WebGL, WebCL, OpenVX, OpenVG, EGL, COLLADA, glTF, NNEF, OpenKODE, OpenKCAM, StreamInput, OpenWF, OpenSL ES, OpenMAX, OpenMAX AL, OpenMAX IL, OpenMAX DL, OpenML and DevU are trademarks of The Khronos Group Inc. ASTC is a trademark of ARM Holdings PLC, OpenCL is a trademark of Apple Inc. and OpenGL and OpenML are registered trademarks and the OpenGL ES and OpenGL SC logos are trademarks of Silicon Graphics International used under license by Khronos. All other product names, trademarks, and/or company names are used solely for identification and belong to their respective owners.