Hi Matt,
On 26-11-11 03:55, mattschinkel wrote:
I just wanted to mention that the below is not always correct. Some
glcd's may use 0 for black and 1 for white. Seb and I actually
discussed this :)
const byte GLCD_BACKGROUND_COLOR = 0 -- white
const GLCD_PEN_COLOR = 1 -- black
I didn't follow with much interest the discussions about glcd libraries
because at that time I had none (and I didn't look back).
What I understand by reading glcd_common library is that these are the
defaults, unless the device-dependent glcd_library hasn't declared 'm.
These names are declared in the glcd_ks0108 library. And these are
decalred as variables such that the application can change them, which I
also do in the samples I provided.
I see the same in the libraries for Nokia_3310 and Stm-32qvt.
So I don't see the problem.
Also, your sbyte*3 may not always be needed. Is your glcd> 256 pixels
for both X and Y? See constants GLCD_X_SIZE& GLCD_Y_SIZE. I think
this was mentioned in the issue as well.
The glcd_ellipse procedure uses formula like
x_change = yr * yr * (1- 2 * xr)
stopping_x = two_b_square * xr
When using swords (with 15 significant bits) the maximum radious of a
circle that would guaranteed not to cause overflow is only 25! So even
on a 64x64 display you cannot draw a circle touching the edges of the
display.
When using sbyte*3 (23 significant bits) the maximum radious of a circle
would be 161.
Note: I think my calculations are correct, but please check (your math
may be a little more up to date than mine!).
The limits for ellipses are somewhat more difficult to calculate because
of the mix of xr and yr in the intermediate results.
Maybe the variables could be optimized a little more like some sbyte*3,
some sword. But is it really so helpful? The variables are local to the
procedure, so the RAM can be re-used outside the procedure.
Maybe use a if statement, or even try something like this:
var sbyte*(2+GLCD_X_SIZE) x = 1234
It is not as easy as that! Firstly the minimum for GLCD_X_SIZE is 1, so
this formula would result in sbyte*3, which is what we already have now.
Better would be (1+GLCD_X_SIZE). Secondly the required size depends on
both on the desired x and y radii. Thirdly when you want to draw part of
a circle or ellipse the x or y radius could be larger than half of the
physical x- or y-dimension of the display.
To be continued.....
Regards, Rob.
--
R. Hamerling, Netherlands --- http://www.robh.nl
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