Re: a graphics issue I can not figure out

On Mar 4, 2020, at 3:58 PM, Nathan smith <[email protected]> wrote:
> 
> My goal was to create a grid and then plot some lines upon it.
> 
> I have got the grid working, but I can not seem to position a triangle correctly.

I have a bad habit of making stylistic comments about submitted code.

You should not be storing “dc” and “pen” in a member.  That is, you should use “dc” and “pen”, not “self.dc” and “self.pen”.  You need those objects to evaporate when the function returns, otherwise things don’t get cleaned up.

You can draw the horizontal and vertical grid lines in a single loop:

x0 = g.center_point[0]-6*38
y0 = g.center_point[1]-6*38
x1 = g.center_point[0]+5*38
y1 = g.center_point[1]+5*38
for x in range(11):
    dc.DrawLine( x0, y0+x*38, x1, y0+x*38 )
    dc.DrawLine( x0+x*38, y0, x0+x*38, y1 )

Rufus nailed your other issue.  (0,0) in Windows, X, and MacOS is the upper left and Y increases going down.  In Postscript and OS/2, (0,0) is the lower left and Y increases going up.

I hope you realize that 38 pixels per centimeter is only a rough approximation.  Windows lies about the actual pixel size, because in reality it has no idea how large your monitor is physically.  38 per centimeter maps to 96 pixels per inch.  A 22” monitor running full HD would be 96 dpi, but most people have pixels bigger than that.
— 
Tim Roberts, [email protected]
Providenza & Boekelheide, Inc.

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