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diff --git a/src/livarot/AlphaLigne.h b/src/livarot/AlphaLigne.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/** @file
+ * TODO: insert short description here
+ *//*
+ * Authors:
+ * see git history
+ * Fred
+ *
+ * Copyright (C) 2018 Authors
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#ifndef my_alpha_ligne
+#define my_alpha_ligne
+
+#include "LivarotDefs.h"
+
+/*
+ * pixel coverage of a line, libart style: each pixel coverage is obtained from the coverage of the previous one by
+ * adding a delta given by a step. the goal is to have only a limited number of positions where the delta != 0, so that
+ * you only have to store a limited number of steps.
+ */
+
+// a step
+struct alpha_step {
+	int           x;     // position
+	float         delta; // increase or decrease in pixel coverage with respect to the coverage of the previous pixel
+};
+
+
+class AlphaLigne {
+public:
+  // bounds of the line
+  // necessary since the visible portion of the canvas is bounded, and you need to compute
+  // the value of the pixel "just before the visible portion of the line"
+	int          min,max;
+	int          length;
+
+  // before is the step containing the delta relative to a pixel infinitely far on the left of the line
+  // thus the initial pixel coverage is before.delta
+	alpha_step   before,after;
+  // array of steps
+	int          nbStep,maxStep;
+	alpha_step*  steps;
+	
+  // bounds of the portion of the line that has received some coverage
+	int          curMin,curMax;
+
+  // iMin and iMax are the bounds of the visible portion of the line
+	AlphaLigne(int iMin,int iMax);
+    virtual ~AlphaLigne();
+
+  // empties the line
+	void             Reset();
+  
+  // add some coverage.
+  // pente is (eval-sval)/(epos-spos), because you can compute it once per edge, and thus spare the
+  // CPU some potentially costly divisions
+	int              AddBord(float spos,float sval,float epos,float eval,float iPente);
+  // version where you don't have the pente parameter
+	int              AddBord(float spos,float sval,float epos,float eval);
+
+  // sorts the steps in increasing order. needed before you raster the line
+	void             Flatten();
+	
+  // debug dump of the steps
+	void						 Affiche();
+
+  // private
+	void             AddRun(int st,float pente);
+
+  // raster the line in the buffer given in "dest", with the rasterization primitive worker
+  // worker() is given the color parameter each time it is called. the type of the function is 
+  // defined in LivarotDefs.h
+	void             Raster(raster_info &dest,void* color,RasterInRunFunc worker);
+	
+  // also private. that's the comparison function given to qsort()
+	static int       CmpStep(const void * p1, const void * p2) {
+		alpha_step* d1=(alpha_step*)p1;
+		alpha_step* d2=(alpha_step*)p2;
+		return  d1->x - d2->x ;
+	};
+};
+
+
+#endif
+