A different idea for helper drawing method in GBA graphics mode 4 that won't work

gfx.c

void drawPixel_mode4(int x, int y, u8 color)
{
    u16 *here = (REG_DISPCNT & BACKBUFFER ? VideoBuffer : BackBuffer) + x%(SCREEN_WIDTH/2) + y*(SCREEN_WIDTH/2);
    *here = color + (*here & 0xFF00);
}

void drawRect_mode4(int x, int y, int w, int h, u8 c)
{
    u16 *currentBackBuffer = REG_DISPCNT & BACKBUFFER ? VideoBuffer : BackBuffer;
    int ix, iy;
    for (ix = x/2; ix < (x+w)/2; ix++)
        for (iy = y; iy < y+h; iy++)
                (currentBackBuffer)[ ix%(SCREEN_WIDTH/2) + iy*(SCREEN_WIDTH/2) ] = c + (c<<8);
    if ((x+w)%2 == 1) // odd width, draw last single-pixel line (ix < (x+w)/2 in the previous loop truncated)
        for (iy = y; iy < y+h; iy++)
            drawPixel_mode4(x+w+1, iy, c);
}