Dynamically generates impostor textures from given mesh object(Skateboard). The impostor texture is updated due to relative movement of impostor target object from the viewing camera.

Impostor mesh is not updated when the camera viewing angle to the impostor does not exceed the defined threshold(Angle Threshold). Original threshold is set to 0.02. As the threshold is increased, the impostor does not be updated frequently and cause some artifacts which comes from angle difference between the camera angle of current view and camera angle of render texture.

Target object which is to be rendered with the impostor is initially set to the Skateboard object, but you can change the target object using parameter box of Inspector or source code of ImpostorController.cs.

• Angle Threshold(float) : Threshold for selective update. Until the angle difference of impostor view is exceed this threshold, rendering update is not processed.
• Texture Size(int) : Size of RenderTexture

• TextureManager.cs : Container class of RenderTexture and Camera for Texture rendering
• ImpostorController.cs : Main Controller class which assigns TextureManager and update camera position
• AlphaShader.shader : Alpha shader for the render texture composition

1. Create Quad object to be rendered with impostor
2. Link the ImpostorController.cs script to the quad object. (If you don't want to many objects, disable "MultiImposer" class.
3. Set the parameter and excute

When the camera is closer than certain distance, imposter rendered object can be vanished. This is due to the render texture property of unity engine, but this does not happens when at least 2m distance is allowed(which is mentioned in problem condition).

If you set the texture resolution too low, some artifact like aliasing and blur can be seen. In my calculation, over than 400 pixels render texture does not show distinct artifacts.

Enhancement of performance for rendering massive objects using Impostor rendering and selectively update policy. In this part, the massive number of objects can be rendered with the impostor rendering to test performance of massive rendering. Additional methods for performance enhancement are applied and test the result of performance.

Rendering performance enhancement is performed while only rendering necessary impostor and using pre-rendered impostor cache. Detailed policy applied is as below.

• Adaptive Resolution : In rendering massive objects, far objects from view position does not requires high-resolutional impostor texture. With calculation of viewing angle from view point, the impostor texture resolution in far object is reduced. This operation does not support dynamic resolution change since dynamic resizing of RenderTexture in Unity Engine requires additional performance burden.
• Angle Threshold : The same method which is applied to previous single impostor. Skip impostor rendering update when movement of view position is lower than the threshold.
• Frustum Culling : Check if the certain impostor are in the camera frustum and if not, do not update the impostor runtime.
• Pre-rendered Texture Caching : Loads pre-generated texture and use for the impostor rendering instead of dynamically rendering online.

• Target Obj : A mesh object to be rendered with impostor. Default value is the Skateboard object.
• Adaptive Resolution : Turn on/off adaptive resolution method. This method only effect when the program start.
• View Angle Update : View angle threshold method for selective update of impostor.
• Use Cache : loading a pre-rendered texture image and texture mapping instead of dynamic generation.
• Falling Object : Check if the massive objects are falling or not.
• Angle Threshold(float) : Threshold for selective update.
• Cache Angle Threhold : Threshold for texture cache.
• Object Number : The number of objects to be rendered with impostor
• Positioning Method : The way of massive objects positioning. Uniform : uniformly positioned / Random2D : randomly positioned in ground plane / Random3D : randomly positioned in 3D space

• MultiImpostorController.cs : Impostor Controller Class which assigns Multiple TextureManager and update camera position
• UtilFun.cs : Function implementation for additional utility function and parameter setting
• PrintoutImpostorTexture.cs : Pre-generate cache texture for impostor

1. Texture Generation_(Optional)_ : Turn on the Printout Texture of GenerateCacheTex.cs which is attached to GenerateCacheTex game object. The code will generate impostorCacheTex.png file to the home location. Please beware that the pre-generation of impostor rendering requires much time. Texture cache properties are listed in UtilFun.cs TextureCacheInfo class. Texture Size and Cache range, cache resolution are defined.
2. Massive Object Rendering : Input the number of objects to rendered in Object Number at MultiImpostorController script and choose the positioning method among the Uniform/Random2D/Random3D
3. Enhancement Feature Selection : select additional enhancement for the performance and excute it : Adaptive Resolution / View Angle Update / Frustum Culling / Use Cache

• Enhancement Efficiency : Adaptive Resolution enhance efficiency significantly and View Angle Update increases performance of impostor rendering. However, Frustum Culling does not shows distinct difference in framerate. That's because unity3D engine does culling algorithm by itself and manual culling does not effects well.
• Cache Resolution : The pre-rendered texture is used for cache of impostor rendering, but there exists popping artifacts when the pre-rendered angle and current angle has difference. I set the angle threhold for caching as 1.0, but it can be increased when you want to get more performance.

• Scene Files from AltspaceVR

All the source code are from Jong Pil Park([email protected])