MonoGame/MonoGame · error · ArgumentException

startIndex must be at least zero and smaller than data.Lengt

Error message

startIndex must be at least zero and smaller than data.Length.

What it means

ArgumentException('startIndex') from Texture3D.ValidateParams when startIndex < 0 or startIndex >= data.Length. The read/write window must start inside the array before the volume copy proceeds.

Source

Thrown at MonoGame.Framework/Graphics/Texture3D.cs:418

            var width = right - left;
            var height = bottom - top;
            var depth = back - front;

            if (left < 0 || top < 0 || back < 0 || right > texWidth || bottom > texHeight || front > texDepth)
                throw new ArgumentException("Area must remain inside texture bounds");
            // Disallow negative box size
            if (left >= right || top >= bottom || front >= back)
                throw new ArgumentException("Neither box size nor box position can be negative");
            if (level < 0 || level >= LevelCount)
                throw new ArgumentException("level must be smaller than the number of levels in this texture.");
            if (data == null)
                throw new ArgumentNullException("data");
            var tSize = ReflectionHelpers.FastSizeOf<T>();
            var fSize = Format.GetSize();
            if (tSize > fSize || fSize % tSize != 0)
                throw new ArgumentException("Type T is of an invalid size for the format of this texture.", "T");
            if (startIndex < 0 || startIndex >= data.Length)
                throw new ArgumentException("startIndex must be at least zero and smaller than data.Length.", "startIndex");
            if (data.Length < startIndex + elementCount)
                throw new ArgumentException("The data array is too small.");

            var dataByteSize = width*height*depth*fSize;
            if (elementCount * tSize != dataByteSize)
                throw new ArgumentException(string.Format("elementCount is not the right size, " +
                                            "elementCount * sizeof(T) is {0}, but data size is {1}.",
                                            elementCount * tSize, dataByteSize), "elementCount");
        }
	}
}

View on GitHub (pinned to 1d71bbd0ff)

Solutions

1. Clamp or verify startIndex to [0, data.Length - 1] before the call.
2. Ensure data has at least one element when elementCount > 0.
3. Recompute the offset whenever the buffer is resized or sliced.

Example fix

// before
texture.SetData(0, l, t, r, b, f, bk, data, offset, count); // offset may be out of range

// after
int start = Math.Clamp(offset, 0, data.Length - 1);
texture.SetData(0, l, t, r, b, f, bk, data, start, count);

if (data == null || data.Length == 0)
    throw new InvalidOperationException("data must be non-empty");
if (startIndex < 0 || startIndex >= data.Length)
    throw new ArgumentOutOfRangeException(nameof(startIndex));
texture.SetData(level, l, t, r, b, f, bk, data, startIndex, elementCount);

try
{
    texture.SetData(level, l, t, r, b, f, bk, data, startIndex, elementCount);
}
catch (ArgumentException ex) when (ex.ParamName == "startIndex")
{
    // clamp and retry
}

When it happens

Trigger: Calling a box-level SetData/GetData with startIndex < 0, startIndex >= data.Length, or with an empty array (data.Length == 0 fails every startIndex >= 0).

Common situations: Off-by-one offset into a shared volume buffer; negative index; zero-length array; offset not reset after resizing the buffer.

Related errors

• Neither box size nor box position can be negative
• The data array is too small.
• startIndex must be at least zero and smaller than data.Lengt
• The data array is too small.
• Area must remain inside texture bounds

AI-assisted analysis of MonoGame/MonoGame@1d71bbd0ff (2026-08-13). Data as JSON: /api/errors/203a6086fe2f46b0. Report an issue: GitHub.