We often implement processes that dynamically create and destroy RenderTexture in real time from Unity scripts. However, if this creation and destruction are not properly considered, the GPU's video memory (VRAM) will accumulate over time after the game is started, eventually causing a memory leak problem that will cause the app to crash due to out of memory.

In this article, we will explain in detail the mechanism by which "silent leak" occurs in dynamic RenderTexture processing and the correct cleanup method to safely reclaim memory.

For beginners: How would you describe this problem in real life?

Let's compare this RenderTexture memory leak problem to "disposable paper cups and trash cans" at a restaurant.

Creating a render texture by writing new RenderTexture(...) in C# is like a store clerk preparing a new paper cup to hold a drink (drawing data). After drinking, the paper cup must be disposed of by throwing it in the trash.

However, RenderTexture is not stored in heap memory, but in a special location called GPU memory (VRAM).

If you just assign null to the variable in the script when discarding it, this is the same as ``The finished glass is left on the table and only the owner (variable) returns home.'' Since there is no owner, no one knows whose cup it belongs to, and the garbage collector does not clean up the top of the GPU, so used cups accumulate on the table. Eventually, the tables will be filled with cups, and the store (game) will be full and will stop operating (crash). To prevent this, before throwing away the cup, you need to ``empty the contents and declare that you no longer want to use it (Release),'' and then ``physically dispose of the cup in the trash can (Destroy).''

Problem symptoms and specific phenomena

When a RenderTexture memory leak occurs, the following symptoms are observed.

  • The RenderTexture usage and VRAM graphs in the Memory item of Profiler keep rising and never go down.
  • When playing on a real device (especially a smartphone or Quest with severe memory limitations), as certain effects are repeated, the game becomes extremely slow and eventually the app crashes.
  • At first glance, it appears to be an unknown bug because VRAM on the GPU side is not released even when normal GC runs.

Possible cause: Why is memory not freed?

RenderTexture consists of two things: a C# wrapper object and a hardware buffer (texture entity) on the GPU side. If a reference is lost in a normal C# class, it will be recovered by GC, but since the GPU-side buffer belongs to an unmanaged area, it will remain allocated if you just cut the C# reference.

To release the GPU-side buffer, you must explicitly call Release() to send a notification to the graphics card that ``this buffer will no longer be used.'' It is also necessary to call Destroy() to free the wrapper memory on the C# side, and unless you do both, memory will continue to leak.

Specific solutions and approaches

This is an example of correct cleanup implementation for dynamically generating RenderTexture and completely erasing it from memory when it is no longer needed.

1. Implementing the correct cleanup function

using UnityEngine;

public class DynamicTextureManager : MonoBehaviour
{
    private RenderTexture dynamicRT;

    void CreateTexture()
    {
        ReleaseRenderTexture();
        dynamicRT = new RenderTexture(1024, 1024, 16, RenderTextureFormat.ARGB32);
        dynamicRT.Create();
    }

    private void ReleaseRenderTexture()
    {
        if (dynamicRT != null)
        {
            // 1. Immediately release allocated buffers on the GPU side
            dynamicRT.Release();

            // 2. Discard the wrapper object on the C# side
            if (Application.isPlaying)
            {
                Destroy(dynamicRT);
            }
            else
            {
                DestroyImmediate(dynamicRT);
            }

            dynamicRT = null;
            Debug.Log("RenderTexture has been safely released.");
        }
    }

    void OnDestroy()
    {
        ReleaseRenderTexture();
    }
}

2. Considering buffer reuse with RenderTexture.GetTemporary

If you want to use a temporary texture for a short period of time, instead of new every frame, borrow from the temporary buffer pool (RenderTexture.GetTemporary). After use, be sure to return it to the pool with RenderTexture.ReleaseTemporary. 

// Borrow a temporary texture from the pool
RenderTexture tempRT = RenderTexture.GetTemporary(512, 512, 0);

// Execution of drawing processing, etc.

// Be sure to return it to the pool after use (*Do not discard it)
RenderTexture.ReleaseTemporary(tempRT);

Confirmation checklist useful in practice

This is a practical checklist for preventing memory leaks caused by RenderTexture.

If you use
Confirmation items Confirmation/remedy procedure
Release on OnDestroy When a GameObject with a script is destroyed, is the release process running within OnDestroy?
GetTemporary vs. ReleaseGetTemporary, are you sure that ReleaseTemporary is called using the equivalent route?
Monitoring with Profiler Run Profiler's Memory and check whether the number of RenderTexture continues to increase over time.

Summary

Dynamic generation of RenderTexture is essential for rich graphics representation, but it is the developer's responsibility to free memory from unmanaged areas. Build a game without VRAM leaks with a two-step cleanup using Release() and Destroy() or thorough pool management with RenderTexture.GetTemporary.