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Improve gdispDrawThickLine() when the line length is short.

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This commit is contained in:
Joel Bodenmann 2013-12-14 23:30:39 +01:00
parent f624df29e8
commit 87a7658b57
1 changed files with 23 additions and 2 deletions
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25
src/gdisp/gdisp.c
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@ -2587,18 +2587,39 @@ void gdispGDrawBox(GDisplay *g, coord_t x, coord_t y, coord_t cx, coord_t cy, co
/* Normalize the normal vector to length width.
* This uses Newton-Raphson to avoid the need for floating point sqrt.
* We try to solve f(div) = div^2 - len/width^2.
* We try to solve f(div) = div^2 - len/width^2 = 0.
* The closed-form solution is div = sqrt(len) / width.
*/
{
int32_t div, len, tmp;
uint8_t i;
len = nx*nx + ny*ny;
len = (int32_t)nx*nx + (int32_t)ny*ny;
div = 100; /* Initial guess for divider; not critical */
/* If the line length is quite short, premultiply the vector
* in order to get better accuracy in width. */
if (len < 1024)
{
nx <<= 8;
ny <<= 8;
len <<= 16;
}
else if (len < 65536)
{
nx <<= 4;
ny <<= 4;
len <<= 8;
}
int prev = div;
for (i = 0; i < 5; i++) {
tmp = width * width * div;
div -= (tmp * div - len) / (2 * tmp);
if (div == prev)
break; // No change, iteration complete
prev = div;
}
nx = rounding_div(nx, div);