Release v0.6.25: recognize pencil strokes as straight lines

tests/stroke_improvement.h

@@ -1,6 +1,35 @@
 #pragma once
 inline void testStrokeImprovement() {
     auto require=[](bool ok,const char *message){if(!ok) throw std::runtime_error(message);};
+    for(double angle:{0.0,.37,1.57079632679,2.8}) for(bool reverse:{false,true}) {
+        std::vector<POINT> p;
+        for(int i=0;i<=20;++i) {
+            double x=i*10,y=i==0 || i==20?0:(i%3)-1;
+            p.push_back({LONG(std::lround(300+x*std::cos(angle)-y*std::sin(angle))),
+                         LONG(std::lround(300+x*std::sin(angle)+y*std::cos(angle)))});
+        }
+        if(reverse) std::reverse(p.begin(),p.end());
+        bool line=false; ks::ScreenshotShape shape{};
+        auto result=ks::improveScreenshotStroke(p,&shape,&line);
+        require(line && shape==ks::ScreenshotShape::None && result.size()==2 &&
+                result.front().x==p.front().x && result.front().y==p.front().y &&
+                result.back().x==p.back().x && result.back().y==p.back().y,
+                "recognize noisy lines at arbitrary angles and preserve directed endpoints");
+    }
+    for(auto p:std::vector<std::vector<POINT>>{
+        {{0,0},{50,1},{100,0}}, {{0,0},{0,0},{50,0},{100,0}}}) {
+        bool line=false;
+        require(ks::improveScreenshotStroke(p,nullptr,&line).size()==2 && line,
+                "recognize sparsely sampled lines and repeated mouse positions");
+    }
+    for(auto p:std::vector<std::vector<POINT>>{
+        {{0,0},{8,1},{16,0}}, {{0,0},{50,0},{40,0},{80,0},{100,0}},
+        {{0,0},{25,8},{50,12},{75,8},{100,0}},
+        {{0,0},{50,0},{51,10},{52,0},{100,0}}, {{0,0},{0,0},{0,0}}}) {
+        bool line=true;
+        ks::improveScreenshotStroke(p,nullptr,&line);
+        require(!line,"do not straighten short strokes, retracing, curves, spikes or stationary input");
+    }
     auto path=[](std::vector<POINT> corners) {
         std::vector<POINT> p;
         for(size_t i=1;i<corners.size();++i) for(int j=0;j<25;++j) {