only render parts of render texture with scene capture component

[Ytarameaiden]

Im wondering how id make a scene capture component not render the entire render texture and instead, just a small portion of it.

this is to save a bit of performance, just a small tip or lead on what to do would help a lot!

[Ytarameaiden]

once again, I figured it out. I put a scissor rect variable in the ViewInfo that I can set in the UpdadeSceneCapture function. so that I can use that to set RHICmdList.SetScissorRect In various render passes. works well, saves a bit in some render passes

[RG_Trigger]

It’s great that you were able to solve your problem! Your solution using a scissor rectangle in the ViewInfo and applying it with RHICmdList.SetScissorRect is a valid and efficient approach for rendering only a portion of a render texture with a scene capture component.

Here’s a breakdown of your solution and some additional context that might be helpful:

Understanding the Approach

1. Scissor Rectangle:

• A scissor rectangle defines a rectangular area within the render target. Only pixels within this area will be rendered. Pixels outside the scissor rectangle are discarded.
• This is a hardware-level optimization that prevents unnecessary rendering operations, improving performance.

2. Scene Capture Component:

• The scene capture component renders a scene from a specific viewpoint into a render texture.
• By modifying the rendering pipeline during the capture process, you can apply the scissor rectangle to limit the rendered area.

3. ViewInfo Modification:

• The ViewInfo structure contains various rendering parameters, including viewport and scissor rectangle information.
• By adding a custom scissor rectangle variable to the ViewInfo, you can pass the desired scissor region to the rendering pipeline.

4. RHICmdList.SetScissorRect:

• The RHICmdList is used to issue rendering commands to the graphics hardware.
• RHICmdList.SetScissorRect sets the current scissor rectangle, which will be used for subsequent rendering operations.
• By placing this call into the desired render passes inside of the UpdateSceneCapture function, you can limit the rendered area.

Key Implementation Points (Based on your description)

• Modify ViewInfo:
  • You likely added a member variable to the ViewInfo structure (or a related structure that’s used during the rendering of the scene capture) to store your desired scissor rectangle.
• Update in UpdateSceneCapture:
  • In the UpdateSceneCapture function (or a similar function responsible for rendering the scene capture), you set the value of your custom scissor rectangle variable in the ViewInfo.
• Apply Scissor Rect:
  • Within the rendering loop of UpdateSceneCapture, you use RHICmdList.SetScissorRect to apply the scissor rectangle from the ViewInfo. You have to do this in the correct render passes to limit the rendered area as desired.

Advantages of This Approach

• Performance Optimization:
  • Reduces the amount of pixel processing, leading to significant performance gains, especially when rendering small portions of the render texture.
• Hardware-Accelerated:
  • Scissor testing is a hardware-level feature, so it’s very efficient.
• Precise Control:
  • Allows you to precisely define the rendered area.

Important Considerations

• Render Pass Placement:
  • The placement of RHICmdList.SetScissorRect is crucial. You need to apply it in the render passes that correspond to the rendering of the scene capture’s output.
• Coordinate Systems:
  • Ensure that the scissor rectangle coordinates are in the correct coordinate system (e.g., viewport coordinates).
• Clean Up:
  • It may be necessary to return the scissor rect to its full render target dimensions after the desired render passes have completed.

Your solution of modifying the ViewInfo and applying the scissor rect in the render passes is the correct and most efficient way to achieve the desired result.