I'm having an issue with drawing Arcs with AggPas, and I can't quite put my
finger on it... What's happening is that small arc segments are just not
being drawn... they are not super tiny segments, they should end up being at
least 100 pixels long, but they have a pretty big radius, but the radius itself
is not the issue because I can draw larger arc segments with even larger radii
and they have no issues. It seems to be some combination of parameters.
Basically I am scaling my drawing with a multiplier and when I cross a certain
point, these arcs disappear from the drawing. But I notice this only happens
with the Arc() function, not ArcTo() but I'm using both at the same time.. I'm
using MoveTo(), LineTo, and ArcTo() to draw a highlighted path, and at the same
time Line() and Arc() to draw a centerline so what happens is that as I zoom
out, decreasing the scale, the highlighted path is there, but the centerline
disappears for these arc segments. I've reduced this down to trying to just
draw the arc in question and I still have the same issue, so I know it doesn't
have anything to do with any other functions.
It would not be easy to just use ArcTo() for the centerline as well, because it
would break the path I am building, and if I try to draw the path so far, then
use ArcTo for the centerline, then start another path, I end up with a quite
noticeable overlap in my highlighting where the overlap is highlighted twice...
so it would be nice if I could figure out what's going on with ArcTo()
Here is some test data for one of the arcs that just will not draw with AggPas:
Here is how I am implementing the arc command:
agg^.arc(Drawinfo.gi*pixelscale+Draw_X_offset,Drawinfo.gj*pixelscale+Draw_Y_offset,Drawinfo.r*pixelscale,Drawinfo.r*pixelscale,Drawinfo.ea,Drawinfo.sa);
If Pixelscale drops below a certain point, the arc will not draw. I ran
several tests, then tried it with just hard coded values as follows:
agg^.arc(-600470.258096880350,168254.083748858280,624074.001867781300,624074.001867781300,6.011216001395,6.010880670454);
//Draws Arc
agg^.arc(-540359.532287192330,151479.575373972450,561666.601681003190,561666.601681003190,6.011216001395,6.010880670454);
//Draws Arc
agg^.arc(-486259.879058473110,136382.517836575210,505499.941512902880,505499.941512902880,6.011216001395,6.010880670454);
//Does Not Draw Arc
Any Pixel scales smaller than this result in no arc being drawn.
Now I can draw the same arc with the following code:
total_arc_angle:=Drawinfo.ea-Drawinfo.sa;
If Total_Arc_angle<0 then
Total_Arc_Angle:=Total_Arc_Angle+(2*Pi);
agg^.resetpath;
agg^.moveto(Drawinfo.px*pixelscale+Draw_X_offset,Drawinfo.py*pixelscale+Draw_Y_offset);
If Total_arc_angle > Pi then
agg^.arcto(Drawinfo.r*pixelscale,Drawinfo.r*pixelscale,Total_Arc_Angle,True,True,Drawinfo.gx*pixelscale+Draw_X_offset,Drawinfo.gy*pixelscale+Draw_Y_offset)
Else
agg^.arcto(Drawinfo.r*pixelscale,Drawinfo.r*pixelscale,Total_Arc_Angle,False,True,Drawinfo.gx*pixelscale+Draw_X_offset,Drawinfo.gy*pixelscale+Draw_Y_offset);
agg^.drawPath(StrokeOnly);
With this I also performed the same 3 tests as above with the following:
agg^.moveto(609.165546484752,409.256438718313);
agg^.arcto(624074.001867781300,624074.001867781300,0.000335330941,False,True,665.125058651162,609.784932227478);
// Draws Arc
agg^.moveto(611.948991836276,419.230794846482);
agg^.arcto(561666.601681003190,561666.601681003190,0.000335330941,False,True,662.312552786046,599.706439004730);
//Draws Arc
agg^.moveto(614.454092652649,428.207715361834);
agg^.arcto(505499.941512902880,505499.941512902880,0.000335330941,False,True,659.781297507441,590.635795104257);
//Draws Arc
With MoveTo and ArcTo, I can draw the arc any size, even reducing the pixel
scale down so far that the entire drawing is 1 pixel
Does anyone know what's going on with this? It seems like the kind of thing
where some internal calculation does not have enough precision, or something is
overflowing.. but it's strange that ArcTo always works to draw the same exact
arc.
James
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