看了一下 GUILite 的代码，其中的画线没有乘法操作，很好，其实他的一个除以 2 的操作也可以去掉，现在也写一个画圆的程序，尽量少用乘法。后来看到 Bresenham 做图法，更通用更好，都是一个学习的过程。
Bresenham //draw_pixel 中间的乘法应该可以简化， //不过这个里主要是画圆，这里不考虑 int draw_pixel(unsigned char *data, int width , int height, int x0, int y0, int x, int y, int color) { int y2 = y + y0; int x2 = x + x0; if(y2 < 0 || y2 > height){ return -1; } if(x2 < 0 || x2 > width){ return -1; } int offset = y2 * width; unsigned char *p = data + offset + x2 ; p[0] = color; return 0; } int draw_circle(unsigned char *data, int width, int height, int x0, int y0, int r, int color) { int x, y; int r2 = r*r; int prev = 0; int y2 = r2; for(x = 0, y = r; x <= r && y >= 0; x++){ int diff; int diff2; int x2 = prev;// = x^2 int x21 = x2 + x + x + 1;// = (x + 1)^2 prev = x21; while(y >= 0){ diff = x2 + y2 - r2; diff2 = x21 + y2 - r2; draw_pixel(data, width, height, x0, y0, x, y, color); draw_pixel(data, width, height, x0, y0, -x, y, color); draw_pixel(data, width, height, x0, y0, x, -y, color); draw_pixel(data, width, height, x0, y0, -x, -y, color); if(abs(diff) <= abs(diff2)){ y2 = y2 - y - y + 1; // = (y - 1) ^ 2 y--; }else{ break; } } } return 0; }
