/// <summary>
/// Virtually expands the atlas from its initial size to its maximum size.
/// </summary>
/// <remarks>
/// The areas are built by doubling horizontally and vertically, over and over. Consider the following example,
/// where the initial atlas size is 64x64 and the maximum size is 256x256. The resulting 5 areas would be:
/// 1: First area determined by the initial atlas size
/// 2: Area generated by horizontal expansion
/// 3: Area generated by vertical expansion
/// 4: Area generated by horizontal expansion
/// 5: Area generated by vertical expansion - final expansion
/// _______________________
/// | |
/// | |
/// | 5 |
/// | |
/// | |
/// |_______________________|
/// | | |
/// | 3 | |
/// |___________| 4 |
/// | | | |
/// | 1 | 2 | |
/// |_____|_____|___________|
///
/// Because of the exponential nature of this process, we don't need to worry about very large textures. For
/// example, from 64x64 to 4096x4096, only 12 iterations are required, leading to 13 areas.
/// </remarks>
private void BuildAreas()
{
AreaNode current = m_FirstUnpartitionedArea;
while (virtualWidth < maxAtlasSize || virtualHeight < maxAtlasSize)
{
RectInt newArea;
if (virtualWidth > virtualHeight)
{
// Double Vertically.
newArea = new RectInt(0, virtualHeight, virtualWidth, virtualHeight);
virtualHeight *= 2;
}
else
{
// Double Horizontally.
newArea = new RectInt(virtualWidth, 0, virtualWidth, virtualHeight);
virtualWidth *= 2;
}
var newAreaNode = AreaNode.Acquire(newArea);
newAreaNode.AddAfter(current);
current = newAreaNode;
}
}
/// <param name="initialAtlasSize">Initial size of the atlas (POT).</param>
/// <param name="maxAtlasSize">Maximum size of the atlas (POT).</param>
public UIRAtlasAllocator(int initialAtlasSize, int maxAtlasSize, int sidePadding = 1)
{
// Validate Size Coherence.
Assert.IsTrue(initialAtlasSize > 0 && initialAtlasSize <= maxAtlasSize);
// Validate POT
Assert.IsTrue(initialAtlasSize == Mathf.NextPowerOfTwo(initialAtlasSize));
Assert.IsTrue(maxAtlasSize == Mathf.NextPowerOfTwo(maxAtlasSize));
m_1SidePadding = sidePadding;
m_2SidePadding = sidePadding << 1;
this.maxAtlasSize = maxAtlasSize;
maxImageWidth = maxAtlasSize;
maxImageHeight = (initialAtlasSize == maxAtlasSize) ? maxAtlasSize / 2 + m_2SidePadding : maxAtlasSize / 4 + m_2SidePadding;
virtualWidth = initialAtlasSize;
virtualHeight = initialAtlasSize;
int maxOpenRows = GetLog2OfNextPower(maxAtlasSize) + 1;
m_OpenRows = new Row[maxOpenRows];
var area = new RectInt(0, 0, initialAtlasSize, initialAtlasSize);
m_FirstUnpartitionedArea = AreaNode.Acquire(area);
BuildAreas();
}
