/// <summary>
/// Computes the weights to apply at each pixel when resizing.
/// </summary>
/// <param name="destinationSize">The destination size</param>
/// <param name="sourceSize">The source size</param>
/// <returns>The <see cref="WeightsBuffer"/></returns>
// TODO: Made internal to simplify experimenting with weights data. Make it protected again when finished figuring out how to optimize all the stuff!
internal unsafe WeightsBuffer PrecomputeWeights(int destinationSize, int sourceSize)
{
float ratio = (float)sourceSize / destinationSize;
float scale = ratio;
if (scale < 1F)
{
scale = 1F;
}
IResampler sampler = this.Sampler;
float radius = MathF.Ceiling(scale * sampler.Radius);
var result = new WeightsBuffer(sourceSize, destinationSize);
for (int i = 0; i < destinationSize; i++)
{
float center = ((i + .5F) * ratio) - .5F;
// Keep inside bounds.
int left = (int)Math.Ceiling(center - radius);
if (left < 0)
{
left = 0;
}
int right = (int)Math.Floor(center + radius);
if (right > sourceSize - 1)
{
right = sourceSize - 1;
}
float sum = 0;
WeightsWindow ws = result.GetWeightsWindow(i, left, right);
result.Weights[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;
}
// Normalise, 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 = wRef / sum;
}
}
/// <inheritdoc/>
protected override unsafe void OnApply(ImageBase <TColor> source, Rectangle sourceRectangle)
{
// Jump out, we'll deal with that later.
if (source.Width == this.Width && source.Height == this.Height && sourceRectangle == this.ResizeRectangle)
{
return;
}
int width = this.Width;
int height = this.Height;
int sourceX = sourceRectangle.X;
int sourceY = sourceRectangle.Y;
int startY = this.ResizeRectangle.Y;
int endY = this.ResizeRectangle.Bottom;
int startX = this.ResizeRectangle.X;
int endX = this.ResizeRectangle.Right;
int minX = Math.Max(0, startX);
int maxX = Math.Min(width, endX);
int minY = Math.Max(0, startY);
int maxY = Math.Min(height, endY);
if (this.Sampler is NearestNeighborResampler)
{
// Scaling factors
float widthFactor = sourceRectangle.Width / (float)this.ResizeRectangle.Width;
float heightFactor = sourceRectangle.Height / (float)this.ResizeRectangle.Height;
using (PixelAccessor <TColor> targetPixels = new PixelAccessor <TColor>(width, height))
{
using (PixelAccessor <TColor> sourcePixels = source.Lock())
{
Parallel.For(
minY,
maxY,
this.ParallelOptions,
y =>
{
// Y coordinates of source points
int originY = (int)(((y - startY) * heightFactor) + sourceY);
for (int x = minX; x < maxX; x++)
{
// X coordinates of source points
targetPixels[x, y] = sourcePixels[(int)(((x - startX) * widthFactor) + sourceX), originY];
}
});
}
// Break out now.
source.SwapPixelsBuffers(targetPixels);
return;
}
}
// Interpolate the image using the calculated weights.
// A 2-pass 1D algorithm appears to be faster than splitting a 1-pass 2D algorithm
// First process the columns. Since we are not using multiple threads startY and endY
// are the upper and lower bounds of the source rectangle.
// TODO: Using a transposed variant of 'firstPassPixels' could eliminate the need for the WeightsWindow.ComputeWeightedColumnSum() method, and improve speed!
using (PixelAccessor <TColor> targetPixels = new PixelAccessor <TColor>(width, height))
{
using (PixelAccessor <TColor> sourcePixels = source.Lock())
using (Buffer2D <Vector4> firstPassPixels = new Buffer2D <Vector4>(width, source.Height))
{
firstPassPixels.Clear();
Parallel.For(
0,
sourceRectangle.Bottom,
this.ParallelOptions,
y =>
{
// TODO: Without Parallel.For() this buffer object could be reused:
using (Buffer <Vector4> tempRowBuffer = new Buffer <Vector4>(sourcePixels.Width))
{
BufferSpan <TColor> sourceRow = sourcePixels.GetRowSpan(y);
BulkPixelOperations <TColor> .Instance.ToVector4(
sourceRow,
tempRowBuffer,
sourceRow.Length);
if (this.Compand)
{
for (int x = minX; x < maxX; x++)
{
WeightsWindow window = this.HorizontalWeights.Weights[x - startX];
firstPassPixels[x, y] = window.ComputeExpandedWeightedRowSum(tempRowBuffer);
}
}
else
{
for (int x = minX; x < maxX; x++)
{
WeightsWindow window = this.HorizontalWeights.Weights[x - startX];
firstPassPixels[x, y] = window.ComputeWeightedRowSum(tempRowBuffer);
}
}
}
});
// Now process the rows.
Parallel.For(
minY,
maxY,
this.ParallelOptions,
y =>
{
// Ensure offsets are normalised for cropping and padding.
WeightsWindow window = this.VerticalWeights.Weights[y - startY];
if (this.Compand)
{
for (int x = 0; x < width; x++)
{
// Destination color components
Vector4 destination = window.ComputeWeightedColumnSum(firstPassPixels, x);
destination = destination.Compress();
TColor d = default(TColor);
d.PackFromVector4(destination);
targetPixels[x, y] = d;
}
}
else
{
for (int x = 0; x < width; x++)
{
// Destination color components
Vector4 destination = window.ComputeWeightedColumnSum(firstPassPixels, x);
TColor d = default(TColor);
d.PackFromVector4(destination);
targetPixels[x, y] = d;
}
}
});
}
source.SwapPixelsBuffers(targetPixels);
}
}
