/// <summary>
/// Determine the real size of the layer, i.e., the smallest rectangle
/// that includes all non-transparent pixels.
/// </summary>
private static Rectangle FindImageRectangle(Surface surface)
{
var rectPos = new Util.RectanglePosition
{
Left = surface.Width,
Top = surface.Height,
Right = 0,
Bottom = 0
};
unsafe
{
// Search for top non-transparent pixel
bool fPixelFound = false;
for (int y = 0; y < surface.Height; y++)
{
if (ExpandImageRectangle(surface, y, 0, surface.Width, ref rectPos))
{
fPixelFound = true;
break;
}
}
// Narrow down the other dimensions of the image rectangle
if (fPixelFound)
{
// Search for bottom non-transparent pixel
for (int y = surface.Height - 1; y > rectPos.Bottom; y--)
{
if (ExpandImageRectangle(surface, y, 0, surface.Width, ref rectPos))
{
break;
}
}
// Search for left and right non-transparent pixels. Because we
// scan horizontally, we can't just break, but we can examine fewer
// candidate pixels on the remaining rows.
for (int y = rectPos.Top + 1; y < rectPos.Bottom; y++)
{
ExpandImageRectangle(surface, y, 0, rectPos.Left, ref rectPos);
ExpandImageRectangle(surface, y, rectPos.Right + 1, surface.Width, ref rectPos);
}
}
else
{
rectPos.Left = 0;
rectPos.Top = 0;
}
}
Debug.Assert(rectPos.Left <= rectPos.Right);
Debug.Assert(rectPos.Top <= rectPos.Bottom);
var result = new Rectangle(rectPos.Left, rectPos.Top,
rectPos.Right - rectPos.Left + 1, rectPos.Bottom - rectPos.Top + 1);
return(result);
}
/// <summary>
/// Check for non-transparent pixels in a row, or portion of a row.
/// Expands the size of the image rectangle if any were found.
/// </summary>
/// <returns>True if non-transparent pixels were found, false otherwise.</returns>
unsafe private static bool ExpandImageRectangle(Surface surface, int y,
int xStart, int xEnd, ref Util.RectanglePosition rectPos)
{
bool fPixelFound = false;
ColorBgra *rowStart = surface.GetRowAddress(y);
ColorBgra *pixel = rowStart + xStart;
for (int x = xStart; x < xEnd; x++)
{
if (pixel->A > 0)
{
// Expand the rectangle to include the specified point.
if (x < rectPos.Left)
{
rectPos.Left = x;
}
if (x > rectPos.Right)
{
rectPos.Right = x;
}
if (y < rectPos.Top)
{
rectPos.Top = y;
}
if (y > rectPos.Bottom)
{
rectPos.Bottom = y;
}
fPixelFound = true;
}
pixel++;
}
return(fPixelFound);
}