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★ 练习题：操作 slice 显示图片

练习题位置： https://tour.go-zh.org/moretypes/18 练习：切片
实现 Pic。它应当返回一个长度为 dy 的切片，其中每个元素是一个长度为 dx，元素类型为 uint8 的切片。当你运行此程序时，它会将每个整数解释为灰度值（好吧，其实是蓝度值）并显示它所对应的图像。 图像的选择由你来定。几个有趣的函数包括 (x+y)/2, xy, x^y, xlog(y) 和 x%(y+1)。 （提示：需要使用循环来分配 [][]uint8 中的每个 []uint8；请使用 uint8(intValue) 在类型之间转换；你可能会用到 math 包中的函数。）

★ 代码

package main import "golang.org/x/tour/pic" func Pic(dx, dy int) [][]uint8 { img := make([][]uint8, dy) for i := 0; i < dx; i++ { img[i] = make([]uint8, dx) } for i := 0; i < dy; i++ { for j := 0; j < dx; j++ { img[i][j] = (uint8)((i+j)/2) } } return img } func main() { pic.Show(Pic) } 在网站上运行，显示效果为：
如果在命令行中运行，结果为：
注：我在cygwin中运行的。 $ ./slice02.exe IMAGE:iVBORw0KGgoAAAANSUhEUgAAAQAAAAEACAIAAADTED8xAAADKElEQVR4nOzVoRHAMAzAQCfX/VduxjDQk8di+mb+mTlnyKB3vYBc9K4XkIs6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANO+AAAA//9hKgMPVczXbQAAAABJRU5ErkJggg== 对其进行 base64 解码，可以得到图片： $ echo -n "iVBORw0KGgoAAAANSUhEUgAAAQAAAAEACAIAAADTED8xAAADKElEQVR4nOzVoRHAMAzAQCfX/VduxjDQk8di+mb+mTlnyKB3vYBc9K4XkIs6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANM6ANO+AAAA//9hKgMPVczXbQAAAABJRU5ErkJggg==" | base64.exe -d > pic.png

• (i+j)/2 显示效果：
  
• i*j 的显示效果：
  
• i^j 的效果：
  
• i*log（y） 的效果：
  
  i*log（y），代码需要改成这样：

package main import "golang.org/x/tour/pic" import "math" func Pic(dx, dy int) [][]uint8 { img := make([][]uint8, dy) for i := 0; i < dy; i++ { img[i] = make([]uint8, dx) } for i := 0; i < dy; i++ { for j := 0; j < dx; j++ { img[i][j] = (uint8)(i*int(math.Log(float64(j)))) } } return img } func main() { pic.Show(Pic) }

• i%(j+1) 的效果：