private void MeasureForward(ref MeasureContext context)
{
var firstContainerDesiredSize = new RadSize();
var lastContainerDesiredSize = new RadSize();
using (var itemInfos = this.layout.GetLines(context.FirstVisibleIndex, true).GetEnumerator())
{
if (itemInfos.MoveNext())
{
firstContainerDesiredSize = this.GenerateContainer(itemInfos.Current);
context.ForwardGeneratedLength += context.GetLength(firstContainerDesiredSize);
context.MaxLength = Math.Max(context.MaxLength, context.GetOppositeLength(firstContainerDesiredSize));
// Take the length portion of the indexed element that is not currently in viewport.
this.HiddenPixels = GridModel.DoubleArithmetics.Floor(context.GetLength(firstContainerDesiredSize) * (context.Index % 1));
context.ForwardGeneratedLength -= this.HiddenPixels;
context.ForwardGeneratedLength = GridModel.DoubleArithmetics.Ceiling(context.ForwardGeneratedLength);
lastContainerDesiredSize = firstContainerDesiredSize;
this.ViewportItemCount++;
}
while (GridModel.DoubleArithmetics.IsLessThan(context.ForwardGeneratedLength, context.AvailableLength) && itemInfos.MoveNext())
{
context.LastVisibleIndex++;
lastContainerDesiredSize = this.GenerateContainer(itemInfos.Current);
context.ForwardGeneratedLength += context.GetLength(lastContainerDesiredSize);
context.MaxLength = Math.Max(context.MaxLength, context.GetOppositeLength(lastContainerDesiredSize));
this.ViewportItemCount++;
}
}
}
private int GenerateBottomBufferItems(int startGenerateIndex, double viewportLength, MeasureContext context)
{
var buffer = viewportLength * context.BufferScale;
var startIndex = startGenerateIndex + 1;
var lastGeneratedIndex = startIndex;
var generatedLengthContext = this.GeneratedLengthContext;
using (var itemInfos = this.Layout.GetLines(startIndex, true).GetEnumerator())
{
var generatedLength = 0.0;
var generatedLengthForward = context.ForwardGeneratedLength;
while (ListViewModel.DoubleArithmetics.IsLessThan(generatedLength - generatedLengthForward, buffer) && itemInfos.MoveNext())
{
var size = this.GenerateContainer(itemInfos.Current, context);
// generatedLength += this.IsHorizontal ? size.Width : size.Height;
generatedLength += generatedLengthContext.GenerateLength(context.GetLength(size));
lastGeneratedIndex++;
}
}
return(lastGeneratedIndex == startIndex ? startGenerateIndex : lastGeneratedIndex + 1);
}
private int GenerateTopBufferItems(int startGenerateIndex, double viewportLength, double startOffset, MeasureContext context)
{
if (startGenerateIndex == 0)
{
return(startGenerateIndex);
}
var buffer = viewportLength * context.BufferScale;
var startBufferOffset = Math.Max(0, startOffset - buffer);
var startIndex = Math.Min((int)this.Layout.SlotFromPhysicalOffset(startBufferOffset), startGenerateIndex);
if (startIndex > 0)
{
startIndex -= 1;
}
var endIndex = startIndex - 1;
var generatedLengthContext = this.GeneratedLengthContext;
using (var itemInfos = this.Layout.GetLines(startIndex, true).GetEnumerator())
{
var generatedLength = 0.0;
while (ListViewModel.DoubleArithmetics.IsLessThan(generatedLength, buffer) && itemInfos.MoveNext())
{
var size = this.GenerateContainer(itemInfos.Current, context);
// generatedLength += this.IsHorizontal ? size.Width : size.Height;
generatedLength += generatedLengthContext.GenerateLength(context.GetLength(size));
endIndex++;
}
}
return(endIndex == startIndex - 1 ? startGenerateIndex : endIndex + 1);
}
private MeasureContext MeasureHorizontalFrozenElements(RadSize availableSize, int frozenContainersCount)
{
var context = new MeasureContext();
context.InitializeForHorizontalMeasure(this, availableSize);
if (frozenContainersCount == 0)
{
return(context);
}
var firstContainerDesiredSize = new RadSize();
var lastContainerDesiredSize = new RadSize();
using (var itemInfos = this.layout.GetLines(context.FirstVisibleIndex, true).GetEnumerator())
{
if (itemInfos.MoveNext())
{
firstContainerDesiredSize = this.GenerateContainer(itemInfos.Current);
context.ForwardGeneratedLength = context.GetLength(firstContainerDesiredSize);
context.MaxLength = Math.Max(context.MaxLength, context.GetOppositeLength(firstContainerDesiredSize));
// Take the length portion of the indexed element that is not currently in viewport.
this.HiddenPixels = GridModel.DoubleArithmetics.Floor(context.ForwardGeneratedLength * (context.Index % 1));
context.ForwardGeneratedLength -= this.HiddenPixels;
context.ForwardGeneratedLength = GridModel.DoubleArithmetics.Ceiling(context.ForwardGeneratedLength);
lastContainerDesiredSize = firstContainerDesiredSize;
this.ViewportItemCount++;
}
while (frozenContainersCount - 1 > context.LastVisibleIndex && GridModel.DoubleArithmetics.IsLessThan(context.ForwardGeneratedLength, context.AvailableLength) && itemInfos.MoveNext())
{
context.LastVisibleIndex++;
lastContainerDesiredSize = this.GenerateContainer(itemInfos.Current);
context.ForwardGeneratedLength += context.GetLength(lastContainerDesiredSize);
context.MaxLength = Math.Max(context.MaxLength, context.GetOppositeLength(lastContainerDesiredSize));
this.ViewportItemCount++;
}
}
return(context);
}
private void MeasureBackwards(ref MeasureContext context)
{
if (context.AvailableLength - context.ForwardGeneratedLength > GridModel.DoubleArithmetics.Ceiling(1d / IndexStorage.PrecisionMultiplier))
{
if (context.FirstVisibleIndex + this.ViewportItemCount < this.layout.VisibleLineCount)
{
var firstContainerDesiredSize = new RadSize();
using (var itemInfos = this.layout.GetLines(context.FirstVisibleIndex - 1, false).GetEnumerator())
{
while (GridModel.DoubleArithmetics.IsLessThan(context.GeneratedLength, context.AvailableLength) && itemInfos.MoveNext())
{
context.FirstVisibleIndex--;
firstContainerDesiredSize = this.GenerateContainer(itemInfos.Current);
context.BackwardGeneratedLength += context.GetLength(firstContainerDesiredSize);
context.MaxLength = Math.Max(context.MaxLength, context.GetOppositeLength(firstContainerDesiredSize));
this.ViewportItemCount++;
}
}
}
}
}
