Image-based lighting (IBL) uses a cube map of the environment to define the lighting in a scene.

The property Texture defines the used environment map. This property must be set to valid cube map- otherwise, the ImageBasedLight is disabled. The texture can be a normal sRGB texture or an RGBM encoded HDR texture; see Encoding. The cube map must contain mipmaps.

When a mesh is shaded, the normal vector is used to look up a color value in the environment map to use for diffuse lighting. Reflection vectors are used to look up color values for specular lighting. This allows a mesh to reflect the environment, like a mirror. The mipmap levels are used to create reflections on materials with different glossiness. Materials with a high SpecularPower, like mirrors, use high resolution mipmap levels. Diffuse lighting and dull materials use low resolution mipmap levels.

ImageBasedLights have a Shape, which can be Infinite or a BoxShape. Lights with an infinite shape cover the whole scene. Usually a level contains only one image-based light with an infinite shape. Lights with a box shape cover only the volume inside the box. This allows to set different image-based lights for different rooms or zones of a level.

The BlendMode determines if the diffuse light contribution of an image-based light is added to the scene (additive blending, BlendMode = 0) or replaces the ambient lighting and other image-based lights (alpha blending, BlendMode = 1). The default is BlendMode = 1, which means that an diffuse light replaces the ambient lighting and other image-based lights.

Note: Image-based lights are usually applied after the ambient light of the scene and before the other lights of the scene. Image-based lights never replace other lights, like directional lights or point lights.

The property FalloffRange can be used to let an image-based light fade out to create smooth blending between different image-based lights or between an image-based light and an area which contains no image-based lights. (Only relevant for box-shaped lights. Infinite lights never fade out.)

Image-based lights have color and intensity, which are used to tint and scale the colors of the environment map. The color of the Texture, the Color, DiffuseIntensity/SpecularIntensity and HdrScale are multiplied to get the final diffuse and specular light intensities which can be used in the lighting equations.

Diffuse only: The SpecularIntensity can be set to NaN to disable the specular light contribution. This creates a pure diffuse light. As mentioned above, the BlendMode determines whether the diffuse light is added to the scene (BlendMode = 0) or replaces the ambient light and other image-based lights (BlendMode = 1).

Specular only: The DiffuseIntensity can be set to NaN to disable the diffuse light contribution. This creates a pure specular light, which can be used for reflections only.

Localized reflections:Usually, environment maps are treated as if the scene in the environment map is infinitely far away. If an image-based light is used to create reflection of a box-shaped room, the reflections will not properly align with the walls of the room. To correct the reflections, EnableLocalizedReflection can be set to . In this case the reflections are computed to fit a given box. This box is either equal to the BoxShape of the light (property Shape) or to an axis-aligned box defined by LocalizedReflectionBox. The box is always aligned with the local space of the LightNode.

Cloning:When the ImageBasedLight is cloned the Encoding and the Texture are not duplicated. These properties are copied by reference.

Usage tips:

• If you only want to add environment map reflections to a game level, add one infinite image-based light with diffuse intensity set to NaN. This way the light only adds reflections and does not influence the ambient light of the scene.
• Image-based lights with a diffuse intensity can be used to replace ambient lighting. Ambient lighting is usually very "flat", e.g. an ambient light adds only one color. An image-based light can create more interesting ambient lighting. For example, if the environment map contains the blue sky and a brown ground, then objects lit by the image-based light will be blue on top and brown at the bottom.
• Image-based lights can also be used to add "light bounces". For example, if the environment map contains a yellow wall, objects near the yellow wall will receive a yellow "bounce light".
• Environment maps defined by image-based lights can be used in effects using the environment map semantics, see e.g. EnvironmentMap.
• To get proper reflections in rooms, create one image-based light per room. Set EnableLocalizedReflection to . Set an AABB in LocalizedReflectionBox which is aligned with the floor, ceiling and walls of the room. LightNodes can be rotated to align with rooms which are not axis-aligned with the world space.
• It is recommended to position the image-based lights at the eye-level of the player and to capture the environment maps from this position.
• If you want to smoothly fade out an image-based light over time, you can fade the BlendMode from 1 (alpha-blend) to 0 (additive), and at the same time fade the DiffuseIntensity and SpecularIntensity to 0. This creates a smooth change in lighting.

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