Rendering Sequence

Unigine has a combination of full deferred renderer with forward rendering techniques:

All opaque (non-transparent) geometry is rendered in the deferred pass
Transparent geometry is rendered in the forward pass.

Before the deferred rendering pass, the engine performs all the necessary calculations. It specifies what nodes should be rendered, the order of rendering, how many lights on the scene and so forth.

This article introduces the detailed Unigine rendering pipeline including all the auxiliary stages which can be skipped by user.

A frame is a complex structure including a lot of different calculations and textures rendering.

Here is a rendering pipeline, all stages are performed during one frame composition. Some stages can be switched off if it is necessary: decals rendering stage, auxiliary pass, post-materials, etc.

During the rendering, the engine initializes necessary texture buffers and most of them not cleared completely (the engine cuts out the sky areas). Some passes just re-use these already created buffers. Such optimizations help to increase the rendering performance.

The schematic representation of the rendering pipeline helps you to understand the major stages of the rendering order.

The schematic representation of the rendering pipeline

During the frame rendering, we will observe the simple test scene with a variety of materials (transparent and opaque), environment probes, decals, planar reflections, different light sources.

A Common pass is the very first step of the rendering sequence. In this pass environment LUTs, Environment cubemap are rendered. These textures are rendered only once before all the geometry on the scene and will be used further for the final screen composition: for scattering rendering and non-dynamic reflections.

	Environment cubemap is composed from 6 pieces (each 256x256 px).
Schematic representation of the 1x256 LUT textures.	LUT textures are represented as 1x256 px textures taken from the current state of the loaded LUT textures for scattering.

In this step, nothing will be rendered at all. This stage prepares the scene before geometry rendering: the engine analyzes the visible part of the scene to know which objects should be drawn and which shouldn't. The engine does the following:

Checks the intersections of objects with frustum (frustum culling) and finds those which present in the frame.
Finds all the light sources on the scene.
Finds all the surfaces that should be rendered (taking into account occluder objects and sectors).
Sorts Lights and Environment Probes by size (from large to small).
Sorts Decal objects by their rendering order.
Sets the Occlusion Query flags to objects that shouldn't be rendered.
Surfaces Batching. All the opaque surfaces are grouped and rendered in batches according to materials assigned , decreasing the number of DIP calls, therefore, increasing the performance.

Occlusion Query works with a delay: it is a very performance-hit operation that requires much time. The optimization is the following: the engine checks the scene asynchronously and sets the "should not be rendered" flag during the Occlusion Query stage. That's why occlusion query runs at least 1 frame late. But the object will be hidden without "hard switching" when the FPS value is high.

After calculations, shadow maps are rendered. The way of rendering these maps depends on a type of the light source. Generated shadow maps will be used in the further rendering stages.

World Light

For the world lights, the engine creates cascaded shadow maps. World Light's shadow map is rendered into the orthographic projection.

The shadow map of the world light source is rendered into texture divided into four parts (since the 4 is the maximum quantity of shadow cascades).

Shadow map of the world light source.

Shadows near the camera have higher resolutions, while shadows that far away from the camera have fewer details.

Rectangular shadow cascades on the final scene.

Notice

You can specify the number of cascades of the World Light source in the Light World tab of the Parameters window.

Omni Light

Omni light sources use perspective projection for shadow maps. It uses 6 cameras that generate shadow maps.

Keep in mind that using a lot of Omni lights can sufficiently decrease the performance.

Proj Light

Shadow maps for Proj light sources are rendered only once because only 1 camera is used.

Notice

It is better to use Proj lights instead of Omni for better performance.

On this stage, the engine renders necessary textures for dynamic (that changed each frame) reflections: cubemaps for environment probes and 2D textures for planar reflections. To render these textures, the engine goes through all rendering pipeline (but misses some passes described below).

Cubemaps are generated by using 6 cameras, planar reflections use only 1 camera. Both render the final image (one more rendering cycle) with some hooks:

Textures use shadow maps, that were already generated in the previous shadow maps rendering pass.
All post effects are ignored.
Final image for dynamic reflections is rendered missing TAA.

The final texture of the dynamic reflections.

This one of the key passes of the rendering: all the opaque geometry is rendered during this pass one-by-one.

In the end of this pass, the engine has the texture (color texture) with all opaque geometry and scattering.

Native Depth Pre-Pass

In this pre-pass, the GPU performs a depth-test for surface culling. The pre-pass is performed only for alpha test and complex materials (like Terrain materials with a lot of layers).

The depth buffer stores native depth values z/w.

The depth data stored in a depth buffer texture format D32F

During this pass, the GPU can discard a pixel (the shading for this pixel won't be calculated).

Filling the GBuffer

During this step of rendering, the engine fills the Gbuffer (Geometry buffer) for shading.

Depth

Depth buffer contains scene objects in the current field of view (found between the near and far clipping planes). Objects are rendered as pure geometric models and stored into this buffer.

The engine also uses native depth.

The depth data stored in a depth buffer texture format D32F

Albedo

Albedo colors buffer stores pure albedo colors of all material textures:

The format of the texture is RGBA8 (RT0):

RGB channels store albedo color values
A channel stores the occlusion value. This channel is optional

Shading

Shading buffer stores the shading information of objects on the scene.

The format of the texture is RGBA8 (RT1):

R channel stores the metalness value
G channel stores the f0 (specular) value
B channel stores the translucent value
A channel stores the microfiber value

Translucency is used to simulate light shine through objects (leaves, for example).

Normal

Normal buffer stores normal vectors for each vertex of geometry which will be necessary to calculate the proper lighting.

The format of the texture is RGBA8 (RT2):

RGB channels store compressed normal values (in view space)
A channel stores the roughness value

Velocity

Velocity buffer stores information about the displacement of pixels per frame. When the image is still the buffer is filled with zero (black) values. These values are necessary to make the temporal anti-aliasing (TAA) and motion blur work correctly.

The format of the texture is RG16F (RT3):

RG channels store pixel displacement values (XY coordinates)

You can disable it if you don't need velocity-related effects: motion blur, TAA, etc.

Material Mask

Material mask texture. The first 8 bits are reserved for post effects, other bits can be used for materials.

The format of the texture is R32U (RT4):

R channel stores material mask value

Lightmap

Lightmap buffer is used to add baked light to the scene.

The format of the texture is RG11B10F (RT5):

RGB channels store lightmap values

Occlusion Query

During the Occlusion query step, the engine excludes objects (geometry, lights and decals) which have the Culled by occlusion query flag enabled from rendering sequence.

Notice

If the render_occlusion_queries console command value is set to 2, the flag won't be taken into account and all objects will be excluded from rendereing sequence.

Occlusion query is an operation with a lot of calculations (i.e. has a huge influence on performance) and it is executed asynchronously. The engine checks object bounds and sets the flag the to renderer if it is necessary. In the next frame, during the Calculation stage, the renderer excludes the object from rendering sequence.

Notice

The Occlusion Query doesn't work, when the camera is inside the object.

Decals

During this step of the deferred pass for opaque objects, the engine renders decals. Decals have been already sorted on the Calculations stage and during this stage the engine performs rendering by using this order.

Decals are rendered by using alpha blending, but since normal and shading textures' A channels are occupied by microfiber and roughness values, the engine copies necessary values into new textures and performs alpha blending.

	New Normal texture (uncompressed) that is used for alpha blending
	New Roughness texture to store Roughness value in R channel, and Microfiber value in G channel.

Notice

If the value of render_decals console variable is set to 0, the engine will skip this rendering stage.

Shoreline Wetness

This rendering stage is responsible for shoreline wetness effect of the Global Water object. The behavior of this step is like in a previous Decals rendering step. So we can call this step Post-Decal Rendering.

The effect is performed by using Compute Shaders and Unordered Access Textures techniques.

Linear Depth, Color Old Reprojection and Unpacked Normals

To perform screen-space effects, the engine renders Linear Depth, Color Old (previous frame) Reprojection and Normal Unpack (screen-space normals) textures.

These textures will be used in Screen-Space Reflections and Screen-Space Global Illumination stages.

Linear depth texture is generated by using G-buffer depth. Mips of linear depth, Color old and normal unpack textures are also created.

SSRTGI

This stage performs the Screen-Space Ray-Traced Global Illumination post-effect during which the engine fills such textures using the Ray Tracing:

SSAO, if the values of render_ssao, render_ssao_ray_tracing console variables are set to 1, defining whether should the SSAO and SSAO Ray Tracing perform.
SSGI, if the values of render_ssgi, render_ssgi_ray_tracing console variables are set to 1, defining whether should the SSGI and SSGI Ray Tracing perform.
Bent Normal, if the value of render_bent_normal_ray_tracing console variable is set to 1, which defines necessity of the Bent Normal performing.

Bent Normal is rendered in RGBA8 texture.

Bent Normal also may have own TAA depending on :

If the noise is enabled and SSRTGI is rendered in full resolution, there is no TAA in this stage.
If the noise is enabled and SSRTGI is rendered in half resolution or quarter resolution, TAA is applied.

	New Ray-Traced SSAO texture
	New Bent Normal texture

Notice

If the value of render_ssrtgi console variable is set to 0, the engine will skip this rendering stage.

Deferred Light Pass

In the deferred light pass the engine creates a buffer (Deferred Light Map) which is a 2D array of RG11B10F textures. The first layer of the array is for diffuse light, the second is for specular (which can be switched off for VR).

Light sources use already generated shadow maps.

All lights sources are rendered one-by-one in the single 2D array to be applied during the Deferred Composite.

Notice

For optimization issues, 1 world light source is always calculated during the Deferred Composite step.
If you have 2 or more world light sources, 1 world light source will always be rendered during the deferred composite, other will be rendered during this step.

	Light sources diffuse layer
	Light sources specular layer

The engine uses tile rendering technique for Omni lights without shadows. With this optimization, the omni light sources are grouped and rendered in batches, decreasing the number of DIP calls, therefore, increasing the performance.

Deferred Reflections

During this stage of rendering, the engine renders all the environment probes that had been already sorted on the calculations stage.

Environment probes are rendered into the 2D array of RGBA16F textures: the first layer contains reflections, the second layer contains ambient light.

The renderer doesn't clear the deferred reflection textures if at least one environment probe has infinite size.

Notice

If there is no environment, the RG11B10F 2D array is used.

	Reflection texture of Environment Probe
	Ambient texture of Environment Probe

Reflection Pass

In the reflection pass, planar dynamic reflections (that had been already rendered) are applied. Dynamic reflections are rendered in the same texture that was used for Deferred Reflections.

Planar dynamic reflection is applied

Auxiliary Pass

Auxiliary pass is a type of custom pass. Materials with Auxiliary pass enabled will be rendered in the auxiliary RGBA8 texture.

Auxiliary texture is often used for different post-effects. It has his own TAA stage.

Notice

The engine will skip this pass if there's no material with enabled Auxiliary pass option and during the Dynamic Reflections pass.

Auxiliary buffer texture

Refractions

On this stage of the pipeline, the refractions are rendered. They are rendered in the Refraction texture and will be applied in the transparent object stage.

Refraction is RGBA8 texture. The texture contains distortion values.

Notice

This pass is skipped during the Dynamic Reflections pass.

Refractions buffer texture

Transparent Blur Surfaces

On this stage are rendered the transparent surfaces which are used in Transparent Blur effect. They are rendered in the Transparent Blur texture and will be applied in the post effects stage.

Transparent Blur is R16F texture, it contains blurriness values.

Notice

This pass is skipped during the Dynamic Reflections pass.

Transparent Blur buffer texture

SSR

Screen-space Reflections are rendered in RGBA16F textures. It will be applied to the deferred composite stage.

SSR buffer texture

There are two different types of SSR: with importance sampling and without:

Importance Sampling is On

If the importance sampling is enabled, the rendered doesn't use linear depth texture.

In this case, SSR color texture and SSR velocity texture are rendered. Velocity is used for avoiding artifacts whilst the camera or objects are moving.

SSR has its own TAA stage.

Importance Sampling is Off

In this case, three textures are rendered: SSR velocity, SSR color texture, and ray-length texture. After that, the renderer applies TAA for the SSR.

Three textures mentioned above are used to perform blurring to provide realistic reflection behavior.

SSAO

Screen-space Ambient Occlusion is rendered in its own R8 texture. It will be applied in the deferred composite stage.

SSAO can be rendered with or without noise. This option has influence on TAA:

If the noise is enabled and SSAO is rendered in full resolution, there is no TAA in this stage.
If the noise is enabled and SSAO is rendered in half resolution, this stage has its own TAA.

SSAO texture

Notice

If the value of render_ssrtgi console variable is set to 1 and the SSAO texture had been already filled on the SSRTGI stage, the engine will skip this step.

SSGI

Screen-space Global Illumination is rendered in 1 RG11B10F texture.

SSGI stage also has own TAA.

Notice

If the value of render_ssrtgi console variable is set to 1 and the SSGI texture had been already filled on the SSRTGI stage, the engine will skip this step.

Underwater Fog

In this step, the Underwater Fog texture is initialized and cleared.

The renderer does it here to perform the underwater world lighting correctly.

Deferred Composite

During this stage, the engine uses all the necessary textures from the previous stages and passes to create the final texture with opaque geometry. The engine combines buffers and calculates shading for the final texture of this pass.

In this stage, the renderer calculates the light of the 1 World light and applies it. Environment reflections, ambient, haze (scattering) are also rendered here.

The final image of deferred pass for opaque geometry (excluding the Emission pass and SSS)

NoticeThe final deferred composite texture can be RGBA16F or RG11B10F, depending on the corresponding option enabled.

Emission

Emission pass goes after the deferred composite image created. It applies emission effect over the deferred composite image.

Emission applied

SSS

Subsurface Scattering changes the final deferred texture: it applies the exponential blur.

SSS applied

Almost all transparent objects are rendered in the forward rendering pass.

During the forward pass, the renderer fills the deferred buffers to let forward transparent object participate in post-effects.

Refraction

During this stage of rendering sequence, the refraction texture (which had been already rendered) is applied

Refraction applied

Volumetric Clouds

On this step all the layers of procedural Volumetric Clouds are rendered into the RGBA16F texture using parameters of the clouds_base material.

An example of the Clouds texture content

Due to optimization, the Volumetric Clouds will be rendered in the certain order depending on a couple of states:

Before Water and Transparent Objects - if the value of the render_clouds_transparent_order console command is set to 0 and the current camera is below the water highest point or under the surface.
Between Water and Transparent Objects - if the value of the render_clouds_transparent_order console command is set to 0 and the current camera is placed over the water highest point.
After Water and Transparent Objects - if the value of the render_clouds_transparent_order console command is set to 1.

Water

Water rendering in Unigine is really complex thing: it has its own deferred buffer (called WBuffer) with light and environment probes passes.

FieldHeigth and FieldShoreline

First, FieldHeight and Field Shoreline textures are rendered.

Height

Field Height textures are rendered in a 2D array of R16F or R32F textures (depends on settings). All Field Height textures are packed into 2D array to pass the data to the shader.

Notice

You can specify the format of the texture in the array by using the render_field_precision console command

Shoreline

All Field Shoreline textures are also are packed into 2D array (of RGBA8) to pass the data to the shader.

WBuffer

The renderer initializes the WBuffer.

Notice

The Underwater Fog texture has been already initialized.

Diffuse

The diffuse color of the water is black, and diffuse texture is necessary for decals, that will be displayed over the water surface.

The format of the texture is RGBA8:

RGB channels store decal diffuse values
A channel stores foam values