I'm trying to create a bitmap image, and have the following code:
RenderTargetBitmap renderTargetBitmap = new RenderTargetBitmap();
await renderTargetBitmap.RenderAsync(uielement);
IBuffer pixels = await renderTargetBitmap.GetPixelsAsync();
. . .
var pixelArray = pixels.ToArray();
In order to get a ToArray()
extension, I came across this question. So I added:
using System.Runtime.InteropServices.WindowsRuntime; // For ToArray
To my code. However, when I run, I get the following error:
Exception thrown: 'System.ArgumentException' in System.Runtime.WindowsRuntime.dll
Additional information: The specified buffer index is not within the buffer capacity.
When I drill into the details, it says in the Stack Trace:
at >System.Runtime.InteropServices.WindowsRuntime.WindowsRuntimeBufferExtensions.ToArray(IBuffer source, UInt32 sourceIndex, Int32 count) at >System.Runtime.InteropServices.WindowsRuntime.WindowsRuntimeBufferExtensions.ToArray(IBuffer source)
Is this method of extracting a pixel array still applicable to the UWP? If it is, is there any way to get more detail from this error message?
That method of extracting a pixel array is definitely applicable to UWP. As for the error, the decompiled ToArray()
goes like this:
public static byte[] ToArray(this IBuffer source)
{
if (source == null)
throw new ArgumentNullException("source");
return WindowsRuntimeBufferExtensions.ToArray(source, 0U, checked ((int) source.Length));
}
In other words, it calls the ToArray
overload that takes a start index and a length:
public static byte[] ToArray(this IBuffer source, uint sourceIndex, int count)
{
if (source == null)
throw new ArgumentNullException("source");
if (count < 0)
throw new ArgumentOutOfRangeException("count");
if (sourceIndex < 0U)
throw new ArgumentOutOfRangeException("sourceIndex");
if (source.Capacity <= sourceIndex)
throw new ArgumentException(SR.GetString("Argument_BufferIndexExceedsCapacity"));
if ((long) (source.Capacity - sourceIndex) < (long) count)
throw new ArgumentException(SR.GetString("Argument_InsufficientSpaceInSourceBuffer"));
byte[] destination = new byte[count];
WindowsRuntimeBufferExtensions.CopyTo(source, sourceIndex, destination, 0, count);
return destination;
}
The line(s) almost certainly causing your problem:
if (source.Capacity <= sourceIndex)
throw new ArgumentException(SR.GetString("Argument_BufferIndexExceedsCapacity"));
...and since sourceIndex
is necessarily 0, that would mean that source.Capacity
is also 0.
I suggest you add some instrumentation to your code to inspect the IBuffer
:
RenderTargetBitmap rtb = new RenderTargetBitmap();
await rtb.RenderAsync(element);
IBuffer pixelBuffer = await rtb.GetPixelsAsync();
Debug.WriteLine($"Capacity = {pixelBuffer.Capacity}, Length={pixelBuffer.Length}");
byte[] pixels = pixelBuffer.ToArray();
I think it likely that your problem occurs before the ToArray
call. I'm using the exact same sequence in my own UWP app, getting debug output like so:
Capacity = 216720, Length=216720
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