漸層填充色演算法

方法一：
雙線性插值的方法

1.首先計算縮放比例..bl=2/w...2是原圖寬度(因為只有2個顏色)...w是放大後的寬度
2.開始迴圈,從1迴圈到目標寬度w,假設迴圈變數為i...就用n=i*bl
3.取出n的小數部分存到變數p中..然後合成顏色,目標色R=R1*(1-p)+R2*p  G=G1*(1-P)+G2*p  B=B1*(1-P)+B2*p....R1/G1/B1是起始色的紅/綠/藍色,R2/G2/B2是結束色的紅/綠/藍色.

 

color g_color[3] = {{255, 0, 0, 255}, {0, 255, 0, 255}, {0, 0, 255, 255}};
U8 g_perc[2] = {30, 70};
gradient_color g_gc = {g_color, g_perc, 3};

void fill_gradient_color(S32 x1, S32 y1, S32 x2, S32 y2)
{
 S32 i;
 S32 done = 0;
 S32 w;
 S32 p;
 S32 fill_width;
 S32 x_start = 0, x_end;
 S32 x;
 FLOAT bl;
 FLOAT n, m;
 FLOAT tr, tg, tb;
 color start_color, end_color, c;
 
 gradient_color *gc = &g_gc;

 fill_width = x2 - x1;
 
 for (i = 0; (i < (gc->n - 1) && !done); i++)
 {
  start_color = gc->c[i];
  end_color = gc->c[i + 1];
  p = gc->p[i];
  x_end = x_start + pixtel_percent(fill_width, p);
  if (x_end > fill_width - 1)
  {
   x_end = fill_width - 1;
   done = 1;
  }

  w = x_end - x_start;
  bl = 1.0 / (FLOAT)w;

  c.r = start_color.r;
  c.g = start_color.g;
  c.b = start_color.b;
  c.alpha = start_color.alpha;
  for (x = 1; x <= w; x++)
  {
   S32 tmp;
   n = (FLOAT)x * bl;
   tmp = (S32)n;
   m = n - (FLOAT)tmp;
   gui_draw_vertical_line(y1, y2, x1 + x_start + x, c);

   tr = start_color.r * (1.0 - m) + end_color.r * m;
   tg = start_color.g * (1.0 - m) + end_color.g * m;
   tb = start_color.b * (1.0 - m) + end_color.b * m;
   c.r = (S8) tr;
   c.g = (S8) tg;
   c.b = (S8) tb;   
  }
  x_start = x_end - 1;
 }
}

 

 

方法二：
divisor為漸層寬度，ir,ig,ib 為各色值分量的增量，ir = (R2 - R1) / divisor, ig = (G2 - G1) / divisor, ib = (B2 - B1) / divisor, R1/G1/B1是起始色的紅/綠/藍色,R2/G2/B2是結束色的紅/綠/藍色.然後從初始色值開始，每次繪畫都將色值分量各增加ir,ig,ib。

            for (i = 0; (i < (gc->n - 1) && !done); i++)
            {
                start_color = gc->c[i];
                end_color = gc->c[i + 1];
                p = gc->p[i];
                x_end = x_start + pixtel_percent(fill_width, p);
                if (x_end > fill_width - 1)
                {
                    x_end = fill_width - 1;
                    done = 1;
                }
                divisor = (FLOAT) (x_end - x_start) + 1;
                if (divisor == 0)
                {
                    divisor = 1;
                }
                ir = -(start_color.r - end_color.r) / divisor;
                ig = -(start_color.g - end_color.g) / divisor;
                ib = -(start_color.b - end_color.b) / divisor;
                tr = c.r = start_color.r;
                tg = c.g = start_color.g;
                tb = c.b = start_color.b;
                c.alpha = start_color.alpha;
                for (x = x_start; x <= x_end; x++)
                {
                    gui_draw_vertical_line(y1, y2, x + x1, c);
                    tr += ir;
                    tg += ig;
                    tb += ib;
                    c.r = (S8) tr;
                    c.g = (S8) tg;
                    c.b = (S8) tb;
                }
                x_start = x_end + 1;
            }