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Redis源码分析(五)--- sparkline微线图

            sparkline这个单词,我第一次看的时候,也不知道这什么意思啊,以前根本没听过啊,但是这真真实实的出现在了redis的代码中了,刚刚开始以为这也是属于普通的队列嘛,就把他分在了struct包里了。好来分析完了,与原本我所想的差太大了。sparkline英文中的意思“微线图”,这么说吧,类似于折线图,由一个一个信息点构成。所以看到这个意思,你或许就明白了sparkline.c是干什么用的了吧,就是画图用的。我们看看这个画图的内部结构是什么,画图需要的元素是哪些:

/* sparkline.h -- ASCII Sparklines header file
 *
 * ---------------------------------------------------------------------------
 *
 * Copyright(C) 2011-2014 Salvatore Sanfilippo <antirez@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef __SPARKLINE_H
#define __SPARKLINE_H

/* sparkline是一类信息体积小和数据密度高的图表。目前它被用作一些测量,
 *相关的变化的信息呈现的方式,如平均温度,股市交投活跃。sparkline常常以一组多条的形式出现在柱状图,折线图当中。
 *可以理解为一个图线信息 */
/* A sequence is represented of many "samples" */
/* 可以理解为图像上的一个信息点,有文字,有值的大小 */
struct sample {
    double value;
    char *label;
};

/* 图线信息结构体,包括n个元素点,可以据此描述出图,绘图的可不是直接按点和值直接绘制的 */
struct sequence {
	//当前元素点个数
    int length;
    //总共的文字个数,有些点没有label描述,为NULL
    int labels;
    //元素点列表
    struct sample *samples;
    //元素中的最大值,最小值
    double min, max;
};

/* 定义了一些渲染图时候一些属性操作设置 */
#define SPARKLINE_NO_FLAGS 0
#define SPARKLINE_FILL 1      /* Fill the area under the curve. */
#define SPARKLINE_LOG_SCALE 2 /* Use logarithmic scale. */

struct sequence *createSparklineSequence(void);  //创建图线序列结构体
void sparklineSequenceAddSample(struct sequence *seq, double value, char *label); //在图线序列中添加一个信息点
void freeSparklineSequence(struct sequence *seq);   //释放图线序列
sds sparklineRenderRange(sds output, struct sequence *seq, int rows, int offset, int len, int flags); //渲染图线序列为一个图,其实就是得到一个字符串组成的图
sds sparklineRender(sds output, struct sequence *seq, int columns, int rows, int flags); //方法同上,只是少可一个偏移量

#endif /* __SPARKLINE_H */

我们看到上面的sample结构体其实“信息点”元素的意思了,里面很简单,一个文字label,一个value值,简洁明了,然后sequence就自然是图线了,里面就定义了元素点列表了,里面还有线的长度,和最大值,最小值,信息还挺全面的线。后序的画图操作都是根据这个图线序列结构体操作的。结构体一点都不复杂。但是画图的实现一点都不简单,如何根据给定的一些点信息画出一个类似折线的图线呢,可别忘了,这是要在命令行窗口的图线哦,所以不会像高级语言中的GUI的操作那样很方便,我们看看redis代码中是怎么写的。

/* sparkline.c -- ASCII Sparklines
 * This code is modified from http://github.com/antirez/aspark and adapted
 * in order to return SDS strings instead of outputting directly to
 * the terminal.
 *
 * ---------------------------------------------------------------------------

在sparkline.c中的注释声明,此代码修改自 http://github.com/antirez/aspark,原来是开源的代码实现,但是一开始真的不知道还有这么个叫aspark的东西,都跟BigData里的spark搞混了,然后我点击此地址,官方解释来了:

aspark is a C program to display ASCII Sparklines.
It is completely useless in 2011.

不错,意思就是说aspark就是用来在C程序上显示图线效果的。后来,我看了下,的确代码差不多,redis的代码在上面加了自己的东西,稍稍修改,aspark的图线展现有几种形式,第一种,最简单的展示:

$ ./aspark 1,2,3,4,10,7,6,5
    `-_ 
__-`   `
第二张把行数扩展为更多行,展示更多的数据,上面的这个为2行展示,数据多的时候,调节行数,默认输出2行展示

$ ./aspark 1,2,3,4,5,6,7,8,9,10,10,8,5,3,1 --rows 4
       _-``_   
     _`        
   -`       `  
_-`          `_

当然可以更加可视化,在空白处填充字符,看起来更舒服:

$ ./aspark 1,2,3,4,5,6,7,8,9,10,10,8,5,3,1 --rows 4 --fill
       _o##_   
     _#|||||   
   o#|||||||#  
_o#||||||||||#_
用了"|"符号,很有想象力的哦,最最关键的我们看如何实现这样的效果呢,核心代码如下:

/* Render part of a sequence, so that render_sequence() call call this function
 * with differnent parts in order to create the full output without overflowing
 * the current terminal columns. */
/* 渲染出这个图线信息 */
sds sparklineRenderRange(sds output, struct sequence *seq, int rows, int offset, int len, int flags) {
    int j;
    double relmax = seq->max - seq->min;
    int steps = charset_len*rows;
    int row = 0;
    char *chars = zmalloc(len);
    int loop = 1;
    int opt_fill = flags & SPARKLINE_FILL;
    int opt_log = flags & SPARKLINE_LOG_SCALE;

    if (opt_log) {
        relmax = log(relmax+1);
    } else if (relmax == 0) {
        relmax = 1;
    }

    while(loop) {
        loop = 0;
        memset(chars,' ',len);
        for (j = 0; j < len; j++) {
            struct sample *s = &seq->samples[j+offset];
            //value派上用处了
            double relval = s->value - seq->min;
            int step;

            if (opt_log) relval = log(relval+1);
            //最后会算出相关的step
            step = (int) (relval*steps)/relmax;
            if (step < 0) step = 0;
            if (step >= steps) step = steps-1;

            if (row < rows) {
                /* Print the character needed to create the sparkline */
                /* step控制输出的字符是哪一个 */
                int charidx = step-((rows-row-1)*charset_len);
                loop = 1;
                if (charidx >= 0 && charidx < charset_len) {
                    chars[j] = opt_fill ? charset_fill[charidx] :
                                          charset[charidx];
                } else if(opt_fill && charidx >= charset_len) {
                	//用"|"填充内容,更加可视化
                    chars[j] = '|';
                }
            } else {
                /* Labels spacing */
                if (seq->labels && row-rows < label_margin_top) {
                    loop = 1;
                    break;
                }
                /* Print the label if needed. */
                if (s->label) {
                    int label_len = strlen(s->label);
                    int label_char = row - rows - label_margin_top;

                    if (label_len > label_char) {
                        loop = 1;
                        chars[j] = s->label[label_char];
                    }
                }
            }
        }
        if (loop) {
            row++;
            output = sdscatlen(output,chars,len);
            output = sdscatlen(output,"\n",1);
        }
    }
    zfree(chars);
    return output;
}

由于本人能力有限,有点不太懂里面的具体细节,大概看了下,把变量用到的地方稍稍看了下,上面的代码都是非常优秀的代码,值得我们学习,今天至少让我知道了什么叫sparkline叫什么 了,哈哈。

Redis源码分析(五)--- sparkline微线图