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EdgeTable: Avoid integer truncation when rendering paths with large coordinates

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Previously, if the PathFlatteningIterator returned a line segment with
very large x or y positions, the result of
    roundToInt (iter.y1 * 256.0f)
could be incorrect, if the result was too large to fit in an int.

Using int64_t to store intermediate results, converting to int when
updating the edge table itself produces accurate results for a wider
range of inputs.
This commit is contained in:
reuk 2023-05-30 16:48:40 +01:00
parent 059d98507c
commit 4f67a18a3f
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GPG key ID: FCB43929F012EE5C
1 changed files with 10 additions and 14 deletions
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24
modules/juce_graphics/geometry/juce_EdgeTable.cpp
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@ -46,17 +46,17 @@ EdgeTable::EdgeTable (Rectangle<int> area, const Path& path, const AffineTransfo
t += lineStrideElements;
}
auto leftLimit = scale * bounds.getX();
auto topLimit = scale * bounds.getY();
auto rightLimit = scale * bounds.getRight();
auto heightLimit = scale * bounds.getHeight();
auto leftLimit = scale * static_cast<int64_t> (bounds.getX());
auto topLimit = scale * static_cast<int64_t> (bounds.getY());
auto rightLimit = scale * static_cast<int64_t> (bounds.getRight());
auto heightLimit = scale * static_cast<int64_t> (bounds.getHeight());
PathFlatteningIterator iter (path, transform);
while (iter.next())
{
auto y1 = roundToInt (iter.y1 * 256.0f);
auto y2 = roundToInt (iter.y2 * 256.0f);
auto y1 = static_cast<int64_t> (iter.y1 * 256.0f);
auto y2 = static_cast<int64_t> (iter.y2 * 256.0f);
if (y1 != y2)
{
@ -82,19 +82,15 @@ EdgeTable::EdgeTable (Rectangle<int> area, const Path& path, const AffineTransfo
{
const double startX = 256.0f * iter.x1;
const double multiplier = (iter.x2 - iter.x1) / (iter.y2 - iter.y1);
auto stepSize = jlimit (1, 256, 256 / (1 + (int) std::abs (multiplier)));
auto stepSize = static_cast<int64_t> (jlimit (1, 256, 256 / (1 + (int) std::abs (multiplier))));
do
{
auto step = jmin (stepSize, y2 - y1, 256 - (y1 & 255));
auto x = roundToInt (startX + multiplier * ((y1 + (step >> 1)) - startY));
auto x = static_cast<int64_t> (startX + multiplier * static_cast<double> ((y1 + (step >> 1)) - startY));
auto clampedX = static_cast<int> (jlimit (leftLimit, rightLimit - 1, x));
if (x < leftLimit)
x = leftLimit;
else if (x >= rightLimit)
x = rightLimit - 1;
addEdgePoint (x, y1 / scale, direction * step);
addEdgePoint (clampedX, static_cast<int> (y1 / scale), static_cast<int> (direction * step));
y1 += step;
}
while (y1 < y2);