Blit multiple RTHandle textures and draw them on the screen

This page describes a blit operation that involves multiple RTHandle textures and a custom shader effect. The description uses the DistortTunnel scene from the URP package samples as an example.

The code samples on the page are from the following Scene from the URP Package Samples:

* Assets > Samples > Universal RP > 14.0.9 > URP Package Samples > RendererFeatures > DistortTunnel

The sample Scene uses the following assets to perform the blit operation:

Import URP Package Samples to access the complete source code and the Scene.

For general information on the blit operation, refer to URP blit best practices.

Define the render passes in the Scriptable Renderer Feature

The Renderer Feature defines the render passes necessary for rendering the intermediate textures and for the blit operation.

private DistortTunnelPass_CopyColor m_CopyColorPass;
private DistortTunnelPass_Tunnel m_TunnelPass;
private DistortTunnelPass_Distort m_DistortPass;

The RTHandle variables

Each of three render passes and the renderer feature declare the RTHandle variables to create and process the textures for the sample effect.

For example, the DistortTunnelRendererFeature class declares the RTHandle variables, which it first passes as arguments to the render passes, and then uses the resulting textures in the final render pass (DistortTunnelPass_Distort).

The Distort shader, which the example uses for the final effect, uses the textures from the following code sample.

private RTHandle m_CopyColorTexHandle;
private const string k_CopyColorTexName = "_TunnelDistortBgTexture";
private RTHandle m_TunnelTexHandle;
private const string k_TunnelTexName = "_TunnelDistortTexture";

To create temporary render textures within the RTHandle system, the SetupRenderPasses method in the Renderer Feature uses the ReAllocateIfNeeded method:

RenderingUtils.ReAllocateIfNeeded(ref m_CopyColorTexHandle, desc, FilterMode.Bilinear,
    TextureWrapMode.Clamp, name: k_CopyColorTexName );
RenderingUtils.ReAllocateIfNeeded(ref m_TunnelTexHandle, desc, FilterMode.Bilinear,
    TextureWrapMode.Clamp, name: k_TunnelTexName );

Configure the input and output textures

In this example, the SetRTHandles methods in render passes contain code for configuring the input and output textures.

For example, here is the SetRTHandles method from the DistortTunnelPass_Distort render pass:

public void SetRTHandles(ref RTHandle copyColorRT, ref RTHandle tunnelRT, RTHandle dest)
{
    if (m_Material == null)
        return;
    
    m_OutputHandle = dest;
    m_Material.SetTexture(copyColorRT.name,copyColorRT);
    m_Material.SetTexture(tunnelRT.name,tunnelRT);
}

Perform the blit operation

There are two blit operations in this example.

The first example blit operation is in the DistortTunnelPass_CopyColor render pass. The pass blits the texture rendered by the camera to the RTHandle texture called _TunnelDistortBgTexture.

using (new ProfilingScope(cmd, m_ProfilingSampler))
{
    Blitter.BlitCameraTexture(cmd, m_Source, m_OutputHandle, 0);
}

The second example blit operation is the DistortTunnelPass_Distort render pass.

Before performing the blit, the pass binds two source textures directly to the Material in the SetRTHandles method:

m_Material.SetTexture(copyColorRT.name,copyColorRT);
m_Material.SetTexture(tunnelRT.name,tunnelRT);

And then the pass performs the blit operation:

using (new ProfilingScope(cmd, m_ProfilingSampler))
{
    Blitter.BlitCameraTexture(cmd, m_OutputHandle, m_OutputHandle, m_Material, 0);
}

Additional resources