/// <summary>
/// Computes the weights to apply at each pixel when resizing.
/// </summary>
/// <param name="sampler">The <see cref="IResampler"/></param>
/// <param name="destinationSize">The destination size</param>
/// <param name="sourceSize">The source size</param>
/// <param name="memoryAllocator">The <see cref="MemoryAllocator"/> to use for buffer allocations</param>
/// <returns>The <see cref="KernelMap"/></returns>
public static KernelMap Calculate(
IResampler sampler,
int destinationSize,
int sourceSize,
MemoryAllocator memoryAllocator)
{
float ratio = (float)sourceSize / destinationSize;
float scale = ratio;
if (scale < 1F)
{
scale = 1F;
}
float radius = MathF.Ceiling(scale * sampler.Radius);
var result = new KernelMap(memoryAllocator, destinationSize, radius);
for (int i = 0; i < destinationSize; i++)
{
float center = ((i + .5F) * ratio) - .5F;
// Keep inside bounds.
int left = (int)MathF.Ceiling(center - radius);
if (left < 0)
{
left = 0;
}
int right = (int)MathF.Floor(center + radius);
if (right > sourceSize - 1)
{
right = sourceSize - 1;
}
float sum = 0;
ResizeKernel ws = result.CreateKernel(i, left, right);
result.Kernels[i] = ws;
ref float weightsBaseRef = ref ws.GetStartReference();
for (int j = left; j <= right; j++)
{
float weight = sampler.GetValue((j - center) / scale);
sum += weight;
// weights[j - left] = weight:
Unsafe.Add(ref weightsBaseRef, j - left) = weight;
}
// Normalize, best to do it here rather than in the pixel loop later on.
if (sum > 0)
{
for (int w = 0; w < ws.Length; w++)
{
// weights[w] = weights[w] / sum:
ref float wRef = ref Unsafe.Add(ref weightsBaseRef, w);
wRef /= sum;
}
}
protected override void AfterImageApply(Image <TPixel> source, Image <TPixel> destination, Rectangle sourceRectangle)
{
base.AfterImageApply(source, destination, sourceRectangle);
// TODO: An exception in the processing chain can leave these buffers undisposed. We should consider making image processors IDisposable!
this.horizontalKernelMap?.Dispose();
this.horizontalKernelMap = null;
this.verticalKernelMap?.Dispose();
this.verticalKernelMap = null;
}
/// <inheritdoc/>
protected override void BeforeImageApply(Image <TPixel> source, Image <TPixel> destination, Rectangle sourceRectangle)
{
if (!(this.Sampler is NearestNeighborResampler))
{
// Since all image frame dimensions have to be the same we can calculate this for all frames.
MemoryAllocator memoryAllocator = source.GetMemoryAllocator();
this.horizontalKernelMap = KernelMap.Calculate(
this.Sampler,
this.ResizeRectangle.Width,
sourceRectangle.Width,
memoryAllocator);
this.verticalKernelMap = KernelMap.Calculate(
this.Sampler,
this.ResizeRectangle.Height,
sourceRectangle.Height,
memoryAllocator);
}
}
