Draw anti-aliased lines as LED gamma correction test

[LAutour]

`
#ifndef _swap_int16_t
#define _swap_int16_t(a, b)
{
int16_t t = a;
a = b;
b = t;
}
#endif

//private
void MatrixPanel_I2S_DMA::_steepDrawPixelRGB(bool steep, int16_t x, int16_t y, uint8_t r, uint8_t g, uint8_t b)
{
if (steep) drawPixelRGB888(y,x,r,g,b);
else drawPixelRGB888(x,y,r,g,b);
}

//public
//Wu's line algorithm, fix point version
void MatrixPanel_I2S_DMA::writeLineAA(int16_t x0, int16_t y0, int16_t x1, int16_t y1, uint16_t color)
{
int32_t dx = x1 - x0;
if (dx < 0) dx = -dx;
int32_t dy = y1 - y0;
if (dy < 0) dy = -dy;
if (dx == 0)
{
drawFastVLine(x0, min(y0,y1), dy, color);
return;
}
if (dy == 0)
{
drawFastHLine(min(x0,x1), y0, dx, color);
return;
}
if (dy == dx)
{
drawLine(x0,y0,x1,y1, color);
return;
}

bool steep = dy > dx;
if (steep)
{
_swap_int16_t(x0, y0);
_swap_int16_t(x1, y1);
}
if (x0 > x1)
{
_swap_int16_t(x0, x1);
_swap_int16_t(y0, y1);
}
uint8_t r,g,b;
color565to888(color, r, g, b);

_steepDrawPixelRGB(steep, x0, y0, r, g, b);
_steepDrawPixelRGB(steep, x1, y1, r, g, b);

int32_t gradient = ((y1-y0)<< 16)/(x1-x0);
int32_t y = (y0 << 16) + gradient;
int16_t gcolor;
uint8_t _r,_g,_b;
for (int x = x0 + 1; x <= x1 - 1; x++)
{
gcolor = (y >> 8)& 255;
_r = (r * gcolor) >> 8;
_g = (g * gcolor) >> 8;
_b = (b * gcolor) >> 8;
int16_t _y = y >> 16;
_steepDrawPixelRGB(steep, x, _y, r-_r, g-_g, b-_b);
_steepDrawPixelRGB(steep, x, _y + 1, _r, _g, _b);
y += gradient;
}
}
`
If not correct gamma-table (one pixel with a value of 255 will be noticeably different from two adjacent pixels with a value of 127):

[mrcodetastic]

can you raise a pull request? Please note I've just merged a huge pull into the master branch so things have changed drastically now.