Scale UV by area ration

src/uvunwrap.cpp

@@ -57,6 +57,7 @@ void uvUnwrap(const Outcome &outcome,
     simpleuv::UvUnwrapper uvUnwrapper;
     uvUnwrapper.setMesh(inputMesh);
     uvUnwrapper.unwrap();
+    qDebug() << "Texture size:" << uvUnwrapper.textureSize();
     const std::vector<simpleuv::FaceTextureCoords> &resultFaceUvs = uvUnwrapper.getFaceUvs();
     const std::vector<QRectF> &resultChartRects = uvUnwrapper.getChartRects();
     const std::vector<int> &resultChartSourcePartitions = uvUnwrapper.getChartSourcePartitions();

thirdparty/simpleuv/simpleuv/chartpacker.cpp

@@ -82,11 +82,12 @@ bool ChartPacker::tryPack(float textureSize)
     return true;
 }
 
-void ChartPacker::pack()
+float ChartPacker::pack()
 {
+    float textureSize = 0;
     float initialGuessSize = std::sqrt(calculateTotalArea() * m_initialAreaGuessFactor);
     while (true) {
-        float textureSize = initialGuessSize * m_textureSizeFactor;
+        textureSize = initialGuessSize * m_textureSizeFactor;
         ++m_tryNum;
         if (tryPack(textureSize))
             break;
@@ -96,6 +97,7 @@ void ChartPacker::pack()
             break;
         }
     }
+    return textureSize;
 }
 
 }

thirdparty/simpleuv/simpleuv/chartpacker.h

@@ -11,7 +11,7 @@ class ChartPacker
 public:
     void setCharts(const std::vector<std::pair<float, float>> &chartSizes);
     const std::vector<std::tuple<float, float, float, float, bool>> &getResult();
-    void pack();
+    float pack();
     bool tryPack(float textureSize);
 
 private:
@@ -25,7 +25,6 @@ private:
     size_t m_tryNum = 0;
     float m_textureSizeFactor = 1.0;
     size_t m_maxTryNum = 100;
-    float m_texelSizePerUnit = 1.0f;
 };
 
 }

thirdparty/simpleuv/simpleuv/uvunwrapper.cpp

@@ -316,6 +316,20 @@ void UvUnwrapper::makeSeamAndCut(const std::vector<Vertex> &verticies,
     }
 }
 
+float UvUnwrapper::areaOf3dTriangle(const QVector3D &a, const QVector3D &b, const QVector3D &c)
+{
+    auto ab = b - a;
+    auto ac = c - a;
+    return 0.5 * QVector3D::crossProduct(ab, ac).length();
+}
+
+float UvUnwrapper::areaOf2dTriangle(const QVector2D &a, const QVector2D &b, const QVector2D &c)
+{
+    return areaOf3dTriangle(QVector3D(a.x(), a.y(), 0),
+        QVector3D(b.x(), b.y(), 0),
+        QVector3D(c.x(), c.y(), 0));
+}
+
 void UvUnwrapper::calculateSizeAndRemoveInvalidCharts()
 {
     auto charts = m_charts;
@@ -333,15 +347,35 @@ void UvUnwrapper::calculateSizeAndRemoveInvalidCharts()
             qDebug() << "Found invalid chart size:" << size.first << "x" << size.second;
             continue;
         }
+        float surfaceArea = 0;
+        for (const auto &item: chart.first) {
+            const auto &face = m_mesh.faces[item];
+            surfaceArea += areaOf3dTriangle(QVector3D(m_mesh.vertices[face.indices[0]].xyz[0],
+                    m_mesh.vertices[face.indices[0]].xyz[1],
+                    m_mesh.vertices[face.indices[0]].xyz[2]),
+                QVector3D(m_mesh.vertices[face.indices[1]].xyz[0],
+                    m_mesh.vertices[face.indices[1]].xyz[1],
+                    m_mesh.vertices[face.indices[1]].xyz[2]),
+                QVector3D(m_mesh.vertices[face.indices[2]].xyz[0],
+                    m_mesh.vertices[face.indices[2]].xyz[1],
+                    m_mesh.vertices[face.indices[2]].xyz[2]));
+        }
+        float uvArea = 0;
         for (auto &item: chart.second) {
             for (int i = 0; i < 3; ++i) {
                 item.coords[i].uv[0] -= left;
                 item.coords[i].uv[1] -= top;
             }
+            uvArea += areaOf2dTriangle(QVector2D(item.coords[0].uv[0], item.coords[0].uv[1]),
+                QVector2D(item.coords[1].uv[0], item.coords[1].uv[1]),
+                QVector2D(item.coords[2].uv[0], item.coords[2].uv[1]));
         }
         //qDebug() << "left:" << left << "top:" << top << "right:" << right << "bottom:" << bottom;
         //qDebug() << "width:" << size.first << "height:" << size.second;
+        float ratioOfSurfaceAreaAndUvArea = uvArea > 0 ? surfaceArea / uvArea : 1.0;
+        float scale = ratioOfSurfaceAreaAndUvArea * m_texelSizePerUnit;
         m_chartSizes.push_back(size);
+        m_scaledChartSizes.push_back(std::make_pair(size.first * scale, size.second * scale));
         m_charts.push_back(chart);
         m_chartSourcePartitions.push_back(chartSourcePartitions[chartIndex]);
     }
@@ -350,8 +384,8 @@ void UvUnwrapper::calculateSizeAndRemoveInvalidCharts()
 void UvUnwrapper::packCharts()
 {
     ChartPacker chartPacker;
-    chartPacker.setCharts(m_chartSizes);
-    chartPacker.pack();
+    chartPacker.setCharts(m_scaledChartSizes);
+    m_resultTextureSize = chartPacker.pack();
     m_chartRects.resize(m_chartSizes.size());
     const std::vector<std::tuple<float, float, float, float, bool>> &packedResult = chartPacker.getResult();
     for (decltype(m_charts.size()) i = 0; i < m_charts.size(); ++i) {
@@ -505,6 +539,11 @@ void UvUnwrapper::parametrizeSingleGroup(const std::vector<Vertex> &verticies,
     m_chartSourcePartitions.push_back(sourcePartition);
 }
 
+float UvUnwrapper::textureSize() const
+{
+    return m_resultTextureSize;
+}
+
 void UvUnwrapper::unwrap()
 {
     partition();

thirdparty/simpleuv/simpleuv/uvunwrapper.h

@@ -4,6 +4,8 @@
 #include <map>
 #include <QRectF>
 #include <simpleuv/meshdatatype.h>
+#include <QVector3D>
+#include <QVector2D>
 
 namespace simpleuv 
 {
@@ -16,6 +18,7 @@ public:
     const std::vector<FaceTextureCoords> &getFaceUvs() const;
     const std::vector<QRectF> &getChartRects() const;
     const std::vector<int> &getChartSourcePartitions() const;
+    float textureSize() const;
 
 private:
     void partition();
@@ -38,6 +41,8 @@ private:
     void buildEdgeToFaceMap(const std::vector<Face> &faces, std::map<std::pair<size_t, size_t>, size_t> &edgeToFaceMap);
     double distanceBetweenVertices(const Vertex &first, const Vertex &second);
     double dotProduct(const Vertex &first, const Vertex &second);
+    float areaOf3dTriangle(const QVector3D &a, const QVector3D &b, const QVector3D &c);
+    float areaOf2dTriangle(const QVector2D &a, const QVector2D &b, const QVector2D &c);
     void triangulateRing(const std::vector<Vertex> &verticies,
         std::vector<Face> &faces, const std::vector<size_t> &ring);
     void calculateFaceTextureBoundingBox(const std::vector<FaceTextureCoords> &faceTextureCoords,
@@ -48,10 +53,13 @@ private:
     std::map<int, std::vector<size_t>> m_partitions;
     std::vector<std::pair<std::vector<size_t>, std::vector<FaceTextureCoords>>> m_charts;
     std::vector<std::pair<float, float>> m_chartSizes;
+    std::vector<std::pair<float, float>> m_scaledChartSizes;
     std::vector<QRectF> m_chartRects;
     std::vector<int> m_chartSourcePartitions;
     bool m_segmentByNormal = true;
     float m_segmentDotProductThreshold = 0.00;
+    float m_texelSizePerUnit = 1.0;
+    float m_resultTextureSize = 0;
 };
 
 }