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//------------------------------------------------------------------------------
// Microsoft Avalon
// Copyright (c) Microsoft Corporation, 2001
//
// File: MatrixStack.cs
//------------------------------------------------------------------------------
using System;
using System.Diagnostics;
using System.Collections;
using MS.Internal;
using System.Security;
using System.Security.Permissions;
namespace System.Windows.Media
{
/// <summary> MatrixStack class implementation</summary>
internal class MatrixStack
{
private Matrix[] _items;
private int _size;
#if DEBUG
private static readonly int s_initialSize = 4;
#else
private static readonly int s_initialSize = 40; // sizeof(Matrix) * 40 = 2240 bytes. Must be > 4
#endif
private static readonly int s_growFactor = 2;
private static readonly int s_shrinkFactor = s_growFactor + 1;
// The following members are used to lazily manage the memory allocated by the stack.
private int _highWaterMark;
private int _observeCount;
private static readonly int s_trimCount = 10;
public MatrixStack()
{
_items = new Matrix[s_initialSize];
}
/// <summary>
/// Ensures that there is space for at least one more element.
/// </summary>
private void EnsureCapacity()
{
// If we reached the capacity of the _items array we need to increase
// the size. We use an exponential growth to keep Push in average O(1).
if (_size == _items.Length)
{
Matrix[] newItems = new Matrix[s_growFactor * _size];
Array.Copy(_items, newItems, _size);
_items = newItems;
}
}
/// <summary>
/// Push new matrix on the stack.
/// </summary>
/// <param name="matrix">The new matrix to be pushed</param>
/// <param name="combine">Iff true, the matrix is multiplied with the current
/// top matrix on the stack and then pushed on the stack. If false the matrix
/// is pushed as is on top of the stack.</param>
public void Push(ref Matrix matrix, bool combine)
{
EnsureCapacity();
if (combine && (_size > 0))
{
// Combine means that we push the product of the top matrix and the new
// one on the stack. Note that there isn't a top-matrix if the stack is empty.
// In this case the top-matrix is assumed to be identity. See else case.
_items[_size] = matrix;
// _items[_size] = _items[_size] * _items[_size-1];
MatrixUtil.MultiplyMatrix(ref _items[_size], ref _items[_size - 1]);
}
else
{
// If the stack is empty or we are not combining, we just assign the matrix passed
// in to the next free slot in the array.
_items[_size] = matrix;
}
_size++;
// For memory optimization purposes we track the max usage of the stack here.
// See the optimze method for more details about this.
_highWaterMark = Math.Max(_highWaterMark, _size);
}
/// <summary>
/// Pushes a transformation on the stack. The transformation is multiplied with the top element
/// on the stack and then pushed on the stack.
/// </summary>
/// <param name="transform">2D transformation.</param>
/// <param name="combine">The combine argument indicates if the transform should be pushed multiplied with the
/// current top transform or as is.</param>
/// <remark>
/// The code duplication between Push(ref Matrix, bool) and Push(Transform, bool) is not ideal.
/// However, we did see a performance gain by optimizing the Push(Transform, bool) method
/// minimizing the copies of data.
/// </remark>
public void Push(Transform transform, bool combine)
{
EnsureCapacity();
if (combine && (_size > 0))
{
// Combine means that we push the product of the top matrix and transform
// on the stack. Note that there isn't a top-matrix if the stack is empty.
// In this case the top-matrix is assumed to be identity. See else case.
// _items[_size] is the new top of the stack, _items[_size - 1] is the
// previous top.
transform.MultiplyValueByMatrix(ref _items[_size], ref _items[_size - 1]);
}
else
{
// If we don't combine or if the stack is empty.
_items[_size] = transform.Value;
}
_size++;
// For memory optimization purposes we track the max usage of the stack here.
// See the optimze method for more details about this.
_highWaterMark = Math.Max(_highWaterMark, _size);
}
/// <summary>
/// Pushes the offset on the stack. If the combine flag is true, the offset is applied to the top element before
/// it is pushed onto the stack.
/// </summary>
public void Push(Vector offset, bool combine)
{
EnsureCapacity();
if (combine && (_size > 0))
{
// In combine mode copy the top element, but only if the stack is not empty.
_items[_size] = _items[_size-1];
}
else
{
// If combine is false, initialize the new top stack element with the identity
// matrix.
_items[_size] = Matrix.Identity;
}
// Apply the offset to the new top element.
MatrixUtil.PrependOffset(ref _items[_size], offset.X, offset.Y);
_size++;
// For memory optimization purposes we track the max usage of the stack here.
// See the optimze method for more details about this.
_highWaterMark = Math.Max(_highWaterMark, _size);
}
/// <summary>
/// Pops the top stack element from the stack.
/// </summary>
public void Pop()
{
Debug.Assert(!IsEmpty);
#if DEBUG
_items[_size-1] = new Matrix();
#endif
_size--;
}
/// <summary>
/// Peek returns the matrix on the top of the stack.
/// </summary>
public Matrix Peek()
{
Debug.Assert(!IsEmpty);
return _items[_size-1];
}
///<value>
/// This is true iff the stack is empty.
///</value>
public bool IsEmpty { get { return _size == 0; } }
/// <summary>
/// Instead of allocating and releasing memory continuously while pushing on
/// and popping off the stack, we call the optimize method after each frame
/// to readjust the internal stack capacity.
/// </summary>
public void Optimize()
{
Debug.Assert(_size == 0); // The stack must be empty before this is called.
Debug.Assert(_highWaterMark <= _items.Length);
// After s_trimCount calls to this method we check the past usage of the stack.
if (_observeCount == s_trimCount)
{
int newSize = Math.Max(_highWaterMark, s_initialSize);
if (newSize * (s_shrinkFactor) <= _items.Length)
{
// If the water mark is less or equal to capacity divided by the shrink
// factor, then we shrink the stack. Usually the shrink factor is greater
// than the grow factor. This avoids an oscillation of shrinking and growing
// the stack if the high water mark goes only slightly up and down.
// Note that we don't need to copy the array because the stack is empty.
_items = new Matrix[newSize];
}
_highWaterMark = 0;
_observeCount = 0;
}
else
{
// Keep incrementing our observe count
_observeCount++;
}
}
}
}
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