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Fix ellipse plotter, adhere to sounder invariants this time.

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elasota
2020-01-21 00:09:38 -05:00
parent f5b0ef3698
commit 5e3e666765
2 changed files with 23 additions and 4 deletions
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19
PortabilityLayer/EllipsePlotter.cpp
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@@ -10,6 +10,11 @@ namespace
{
return v * v;
}
static int64_t SquareInt64(int64_t v)
{
return v * v;
}
}
namespace PortabilityLayer
@@ -46,9 +51,9 @@ namespace PortabilityLayer
#if PL_DEBUG_ELLIPSE_PLOTTER
{
const int32_t diameterSq = SquareInt32(m_diameters.m_x*m_diameters.m_y);
const int32_t sqDistX = SquareInt32(m_2offsetFromCenter.m_x*m_diameters.m_y);
const int32_t sqDistY = SquareInt32(m_2offsetFromCenter.m_y*m_diameters.m_x);
const int64_t diameterSq = SquareInt64(m_diameters.m_x*m_diameters.m_y);
const int64_t sqDistX = SquareInt64(m_2offsetFromCenter.m_x*m_diameters.m_y);
const int64_t sqDistY = SquareInt64(m_2offsetFromCenter.m_y*m_diameters.m_x);
assert(m_sqDistFromEdge >= 0);
assert(sqDistX + sqDistY >= diameterSq);
@@ -407,5 +412,13 @@ namespace PortabilityLayer
m_xChangeCostDynamicFactor = offsetFromCenterTimes2.m_x * xCostMultiplier;
m_yChangeCostDynamicFactor = offsetFromCenterTimes2.m_y * yCostMultiplier;
// On very wide ellipses (like 36x4), the point in the last column below the center may not be the first point in the row
// that is outside of the ellipse.
// Since the algorithm here is based on cost minimization, it is allowed to intersect the ellipse if the start and end points
// are both on or outside of the ellipse, so this violates the invariants.
// Therefore, we need to decrement X until this is not the case.
while (m_xChangeCostDynamicFactor - m_xChangeCostStaticFactor < m_sqDistFromEdge)
DecrementX();
}
}