From e87107e89eee4747a9208f5de7b9ee0f0cb19832 Mon Sep 17 00:00:00 2001
From: KoroLion <korolion31@yandex.ru>
Date: Sun, 21 Jun 2020 16:24:54 +0300
Subject: [PATCH] Critical fix: incorrect function conversion

---
 src/function_imaging.pas | 35 +++++++++++++++++++++--------------
 src/gui/gui.pas          |  2 +-
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/src/function_imaging.pas b/src/function_imaging.pas
index 85c2335..8eb9566 100644
--- a/src/function_imaging.pas
+++ b/src/function_imaging.pas
@@ -78,24 +78,33 @@ var
   pxData: TPxData;
   fParser: TFPExpressionParser;
   argX, argY: TFPExprIdentifierDef;
+  fStr: string;
   x, y, intense: integer;
   convX, convY, fRes1, fRes2, pixelRadius: extended;
   dfDx, dfDy, delta, gradLen: extended;
-  ineq: boolean;
+  isInequality, hasEqualSign: boolean;
 begin
   setLength(pxData, args.width, args.height);
-  fParser := TFPExpressionParser.create(nil);
+  fStr := args.f;
   pixelRadius := 1 / args.zoom;
+  delta := 0.00001;
   
-  try
+  isInequality := (pos('>', fStr) <> 0) or (pos('>=', fStr) <> 0) or (pos('<', fStr) <> 0) or (pos('<=', fStr) <> 0); 
+  // line is drawn in point (x, y) if f(x, y) ~= 0
+  // so we changing y = x - 10 to y - (x - 10)
+  hasEqualSign := pos('=', fStr) <> 0; 
+  if (hasEqualSign) then begin
+    fStr := stringReplace(fStr, '=', '-(', []);
+    fStr := fStr + ')';
+  end;
+  
+  try     
+    fParser := TFPExpressionParser.create(nil);
     fParser.builtIns := [bcMath];
     argX := fParser.identifiers.addFloatVariable('x', 0.0);
     argY := fParser.identifiers.addFloatVariable('y', 0.0);
-    //fParser.expression := 'sin(x*x*x * y*y) - cos(x*x * y*y*y)';
-    fParser.expression := args.f;
-    
-    ineq := (pos('>', fParser.expression) <> 0) or (pos('>=', fParser.expression) <> 0) or (pos('<', fParser.expression) <> 0) or (pos('<=', fParser.expression) <> 0); 
-    
+    fParser.expression := fStr;
+              
     for y := 0 to args.height - 1 do begin
       for x := 0 to args.width - 1 do begin
         convX := (x - args.width / 2) / args.zoom + args.centerX;
@@ -107,30 +116,28 @@ begin
           try
             argX.asFloat := convX;
             argY.asFloat := convY;
-            if (ineq) then begin
+            if (isInequality) then begin
               if (fParser.evaluate().resBoolean) then begin
                 pxData[x][y].set_color(0, 0, 0);
               end else begin
                 pxData[x][y].set_color(255, 255, 255);
               end;
             end else begin
-              fParser.expression := stringReplace(fParser.expression, '=', '-', []);
               fRes1 := fParser.evaluate().resFloat;
               
-              // finding derivative of a function at this point (numeric)
-              delta := 0.00001;
-              
+              // calculating df(convX, convY)/dx
               argX.asFloat := convX + delta;
               argY.asFloat := convY;
               fRes2 := fParser.evaluate().resFloat;
               dfDx := (fRes2 - fRes1) / delta;
               
+              // calculating df(convX, convY)/dy
               argX.asFloat := convX;
               argY.asFloat := convY + delta;
               fRes2 := fParser.evaluate().resFloat;
               dfDy := (fRes2 - fRes1) / delta;
               
-              // calculating length of a gradient at this point
+              // calculating length of a gradient at (convX, convY)
               gradLen := sqrt(sqr(dfDx) + sqr(dfDy));
               
               if (abs(fRes1) > (gradLen * pixelRadius)) then begin
diff --git a/src/gui/gui.pas b/src/gui/gui.pas
index 642ed72..329a185 100644
--- a/src/gui/gui.pas
+++ b/src/gui/gui.pas
@@ -222,7 +222,7 @@ begin
     width := '512';
     height := '512';
     fn := 'sin(x*x*x * y*y) = cos(x*x * y*y*y)';
-    zoom := '10';
+    zoom := '100';
     centerX := '0';
     centerY := '0';
   end;