void Tessel::PolygonVertex(Vector V)
{
int index = Mesh::AddVertex(V);
PolygonVertex(index);
}
bool PhysicsInterface::convertImageAlphaTo2DPolygons(const Image& image, Vector<Vector<Vec2>>& outPolygons,
bool flipHorizontally, bool flipVertically)
{
// Check image is valid
if (!image.isValid2DImage())
{
LOG_ERROR << "The passed image is not a valid 2D image: " << image;
return false;
}
auto bitmap = Bitmap(image.getWidth(), image.getHeight());
// Setup bitmap contents
auto width = int(image.getWidth());
for (auto i = 0U; i < bitmap.data.size(); i++)
bitmap.set(i % width, i / width, image.getPixelColor(i % width, i / width).a > 0.5f);
// Find all the edge pixels
auto edgePixels = Vector<PolygonVertex>();
for (auto y = 0; y < bitmap.height; y++)
{
for (auto x = 0; x < bitmap.width; x++)
{
if (bitmap.get(x, y) && (!bitmap.get(x - 1, y - 1) || !bitmap.get(x - 1, y) || !bitmap.get(x - 1, y + 1) ||
!bitmap.get(x, y - 1) || !bitmap.get(x, y + 1) || !bitmap.get(x + 1, y - 1) ||
!bitmap.get(x + 1, y) || !bitmap.get(x + 1, y + 1)))
edgePixels.emplace(x, y);
}
}
while (!edgePixels.empty())
{
// Start the next polygon at an unused edge pixel
auto polygon = Vector<PolygonVertex>(1, edgePixels.popBack());
// Each pixel that is put onto polygon can be backtracked if it leads to a dead end, this fixes problems with
// pointy angles that can cause the edge walking to get stuck.
auto hasBacktracked = false;
while (true)
{
// Continue building this polygon by finding the next adjacent edge pixel
auto adjacentPixel = 0U;
for (; adjacentPixel < edgePixels.size(); adjacentPixel++)
{
if (bitmap.isAdjacent(polygon.back(), edgePixels[adjacentPixel]))
break;
}
// If there was no adjacent edge pixel then this polygon is malformed, so skip it and keep trying to build
// more
if (adjacentPixel == edgePixels.size())
{
if (!hasBacktracked)
{
polygon.popBack();
hasBacktracked = true;
if (polygon.empty())
break;
continue;
}
else
break;
}
// Add the adjacent edge pixel to this polygon
polygon.append(edgePixels[adjacentPixel]);
edgePixels.erase(adjacentPixel);
hasBacktracked = false;
// Check whether this polygon is now complete, at least 4 points are required for a valid polygon
if (polygon.size() < 4 || !bitmap.isAdjacent(polygon[0], polygon.back()))
continue;
// Now that a complete polygon has been constructed it needs to be simplified down as much as possible while
// retaining key features such as large straight edges and right angles
// Simplify perfectly horizontal and vertical edges as much as possible
for (auto i = 0; i < int(polygon.size()); i++)
{
const auto& a = polygon[i];
const auto& b = polygon[(i + 1) % polygon.size()];
const auto& c = polygon[(i + 2) % polygon.size()];
if ((a.x == b.x && a.x == c.x) || (a.y == b.y && a.y == c.y))
polygon.erase((i-- + 1) % polygon.size());
}
// Identify horizontal and vertical edges that are on the outside edge of the bitmap and mark their vertices
// as important
for (auto i = 0U; i < polygon.size(); i++)
{
auto& a = polygon[i];
auto& b = polygon[(i + 1) % polygon.size()];
if ((a.x == 0 || a.x == int(image.getWidth() - 1) || a.y == 0 || a.y == int(image.getHeight() - 1)) &&
a.isAxialEdge(b))
{
a.keep = true;
b.keep = true;
}
}
// Identify axial right angles and flag the relevant vertices as important
for (auto i = 0U; i < polygon.size(); i++)
{
const auto& a = polygon[i];
const auto& c = polygon[(i + 2) % polygon.size()];
auto& b = polygon[(i + 1) % polygon.size()];
if (a.isAxialEdge(b) && b.isAxialEdge(c) && (a - b).isRightAngle(c - b))
b.keep = true;
}
// The ends of straight edges that are not part of a right angle shape are pulled inwards by inserting new
// vertices one pixel apart, this allows the ends of straight edges to undergo subsequent simplification.
// The 'body' of the straight edge is then flagged as important to avoid any further simplification, which
// will preserve the straight edge in the final result.
const auto straightEdgePullBackSize = straightEdgeLength / 3;
for (auto i = 0U; i < polygon.size(); i++)
{
auto a = polygon[i];
auto b = polygon[(i + 1) % polygon.size()];
if (a.isAxialEdge(b))
{
auto xSign = Math::getSign(b.x - a.x);
auto ySign = Math::getSign(b.y - a.y);
if (!a.keep)
{
for (auto j = 0U; j < straightEdgePullBackSize; j++)
polygon.insert(i++, PolygonVertex(a.x + xSign * (j + 1), a.y + (j + 1) * ySign));
polygon[i].keep = true;
}
if (!b.keep)
{
for (auto j = 0U; j < straightEdgePullBackSize; j++)
{
polygon.insert(i++, PolygonVertex(b.x - (straightEdgePullBackSize - j) * xSign,
b.y - (straightEdgePullBackSize - j) * ySign));
}
polygon[i - straightEdgePullBackSize + 1].keep = true;
}
}
}
// This is the main simplification loop, it works by trying to do progressively larger and larger
// simplifcations on the polygon
auto simplificationThreshold = 1.5f;
while (polygon.size() > 3)
{
for (auto i = 0U; i < polygon.size(); i++)
{
const auto& a = polygon[i];
const auto& b = polygon[(i + 1) % polygon.size()];
const auto& c = polygon[(i + 2) % polygon.size()];
// If b is important then don't try to get rid of it
if (b.keep)
continue;
// Get rid of point b if the line a-c is connected by an edge in the bitmap
if (a.distance(c) < simplificationThreshold && bitmap.arePixelsConnectedByEdge(a, c))
polygon.erase((i + 1) % polygon.size());
}
simplificationThreshold += 1.0f;
if (simplificationThreshold >= std::max(image.getWidth(), image.getHeight()))
break;
}
if (polygon.size() < 3)
break;
outPolygons.enlarge(1);
auto& outPolygon = outPolygons.back();
// Scale to the range 0-1
for (const auto& vertex : polygon)
outPolygon.append(vertex.toVec2() / Vec2(float(image.getWidth() - 1), float(image.getHeight() - 1)));
// Apply horizontal and vertical flips if requested
if (flipHorizontally)
{
for (auto& vertex : outPolygon)
vertex.setXY(1.0f - vertex.x, vertex.y);
}
if (flipVertically)
{
for (auto& vertex : outPolygon)
vertex.setXY(vertex.x, 1.0f - vertex.y);
}
// Order vertices clockwise
auto center = outPolygon.getAverage();
if ((Vec3(outPolygon[0]) - center).cross(Vec3(outPolygon[1]) - center).z > 0.0f)
outPolygon.reverse();
break;
}
}
return !outPolygons.empty();
}
