add 3dplot example, small doc fixes

examples/3dplot.pas

@@ -0,0 +1,97 @@
+program threedeeplot;
+const w = 640;
+      h = 400;
+
+var u0,v0:integer;
+
+function fun(x0,y0:real):real;
+const vscale = 50.0;
+      hscale = 20.0;
+
+var x,y,f:real;
+begin
+	x := x0 / hscale;
+	y := y0 / hscale;
+	f := sin(sqrt(x*x + y*y));
+
+	fun := f * vscale;
+end;
+
+procedure plot;
+var maxV,minV:array [0..w] of real;
+    shift:integer;
+    x,y,z:integer;
+    lastZ:integer;
+    numLines:integer;
+    i:integer;
+    u,v,lastU,lastV:integer;
+    color:integer;
+
+  procedure resetCurve;
+  begin
+  	lastU := -1;
+  	lastV := -1;
+  end;
+
+begin
+	for i := 0 to w do
+	begin
+		maxV[i] := -10000;
+		minV[i] :=  10000;
+	end;
+
+	color := 1;
+	shift := 4;
+	x := 0;
+	numLines := 80;
+	u0 := w div 2;
+	v0 := h div 2;
+
+	for i := -(numLines div 2) to numLines do
+	begin
+		resetCurve;
+		x := i * (w div numLines);
+		for y := -w to w do
+		begin
+			z := round(fun(x,y));
+			u := round(y + u0 + i * shift);
+			v := round(-z + v0 - i * shift);
+
+			if (u >= 0) and (u < w) then
+			begin
+				if (v < maxV[u]) and (v > minV[u]) then
+					resetCurve
+				else
+				begin	
+					if (u >= 0) and (u < w) and (v > maxV[u]) then
+						maxV[u] := v;
+					if (u >= 0) and (u < w) and (v < minV[u]) then
+						minV[u] := v;
+
+					if lastZ < z then
+						color := 8
+					else
+						color := 1;
+
+					if (u >= w) or (u < 0) or (v >= h) or (v < 0) then
+						resetCurve
+					else
+					begin				
+						if lastU = -1 then
+							putpixel(u,v,color)
+						else
+							drawline(lastU,lastV,u,v,color);
+					end;
+					lastU := u;
+					lastV := v;
+					lastZ := z;
+				end;
+			end;
+		end;
+	end;
+end;
+
+begin
+	initgraphics;
+	plot;
+end.