Correct way to update virtual texture at runtime?


I’m trying to make a minimap displayed in the game UI, that is updated often, ideally every frame. The minimap must be an image where I can control each pixel’s color.

I followed the documentation here, and I can create a virtual texture, and display it in the game HUD. Once it is created, I can also update it with another call to its Init() function.

However there is a short period of time (<1second), during which the texture disappears, and then it appears again, updated. As I understand it is the time needed to load the texture to the graphics card. This “flashing” is annoying, and could be worked around by using 2 virtual textures drawn on top of each other, then drawing + switching one then the other. But I’m wondering if I’m doing it the way it is intended:

  • is there a better/recommended way to update a virtual texture at runtime?
  • is calling Init() on the texture multiple times (without recreating any texture data) safe memory-wise?
  • is calling Init() on the texture multiple times (without recreating any texture data) safe memory-wise?

Yes, Flax copies data from C# and streams it to the GPU.

  • is there a better/recommended way to update a virtual texture at runtime?

This flashing period is because the engine uploads the texture to the GPU over several frames (by streaming it). For dynamic textures that should be updated every frame or very frequently (like minimap), I would suggest using GPUTexture created manually and updated during rendering using GPUContext.

Here is an example of it:

public class DynamicTextureFromCode : Script
    private GPUTexture _tempTexture;
    private MaterialInstance _tempMaterialInstance;
    private byte[] _data;

    public Material Material;
    public Model Model;

    public override void OnStart()
        // Ensure that model asset is loaded

        // Create new GPU texture
        var texture = new GPUTexture();
        _tempTexture = texture;
        var desc = GPUTextureDescription.New2D(64, 64, PixelFormat.R8G8B8A8_UNorm, GPUTextureFlags.ShaderResource);
        if (texture.Init(ref desc))

        // Use a dynamic material instance with a texture to sample
        var material = Material.CreateVirtualInstance();
        _tempMaterialInstance = material;
        material.SetParameterValue("tex", texture);

        // Add a model actor and use the dynamic material for rendering
        var staticModel = Actor.GetOrAddChild<StaticModel>();
        staticModel.Model = Model;
        staticModel.SetMaterial(0, material);

        // Plug into rendering to update texture at runtime
        MainRenderTask.Instance.PreRender += OnPreRender;

    public override void OnDestroy()
        MainRenderTask.Instance.PreRender -= OnPreRender;

        // Ensure to cleanup resources
        FlaxEngine.Object.Destroy(ref _tempTexture);
        FlaxEngine.Object.Destroy(ref _tempMaterialInstance);

    private unsafe void OnPreRender(GPUContext context, RenderContext renderContext)
        if (!Enabled || !Actor.IsActiveInHierarchy)

        var desc = _tempTexture.Description;
        var size = desc.Width * desc.Height * PixelFormatExtensions.SizeInBytes(desc.Format);
        if (_data == null || _data.Length != size)
            _data = new byte[size];
        fixed (byte* dataPtr = _data)
            // Generate pixels data (linear gradient)
            var colorsPtr = (Color32*)dataPtr;
            var offset = Mathf.Cos(Time.GameTime * 3.0f) * 0.5f + 0.5f;
            for (int y = 0; y < desc.Height; y++)
                float t1 = (float)y / desc.Height;
                var c1 = Color32.Lerp(new Color32((byte)(offset * 255), 0, 0, 1), Color.Blue, t1);
                var c2 = Color32.Lerp(Color.Yellow, new Color32(0, (byte)(144 - offset * 80), 0, 1), t1);
                for (int x = 0; x < desc.Width; x++)
                    float t2 = (float)x / desc.Width;
                    colorsPtr[y * desc.Width + x] = Color32.Lerp(c1, c2, t2);

            // Update texture data on a GPU (send data)
            uint rowPitch = (uint)size / (uint)desc.Height;
            uint slicePitch = (uint)size;
            context.UpdateTexture(_tempTexture, 0, 0, new IntPtr(dataPtr), rowPitch, slicePitch);
            _tempTexture.ResidentMipLevels = 1; // Mark mip-map as available (required for normal textures only)

(I’ll put it in docs later too, as a side note: _tempTexture.ResidentMipLevels = 1 will work on the latest master - I added this property today so you can use source build or simply add RenderTarget flag to the texture so engine will deduct that there is already some data).

And for the material use GPUTexture parameter type (instead of Texture type like in tutorial from docs).

Thank you for the detailed answer! :slight_smile: I’ll try it ASAP.