采摘＆＃34;很好＆＃34;图表标记/规则中的数字超出给定的规则位置集

Question

使用question about picking nice rule/marker interval中的代码我创建了一个代码，用于在图表上呈现规则。

它有0.1的间隔。但我不想显示所有数字，相反，我想增加规则密度，但只标记每一条规则。像这样：

我创建了一个算法，通过将规则间隔乘以一个数字，然后突出显示可以除以结果的规则。我使用fmod因为值当然可以是浮点数：

    // See https://stackoverflow.com/q/361681/607407 for algorithms
    double rule_spacing = tickSpacing(pixels_per_rule);
    // These are the highlighted rules - currently it should be every 2nd rule
    double important_steps = rule_spacing*2.0;
    // Getting the stard draw offset which should be bellow bottom graph corner
    double start = graph_math::roundTo(begin.y, rule_spacing);
    LOGMTRTTIINFO("Legend from "<<start<<" to "<<values.maxYValue<<" by "<<rule_spacing<<", numbers: "<<important_steps<<'\n');
    //Loop until on top
    while(start<=values.maxYValue) {
        int y = pixelForYValue(start);
        // HERE: calculating whether this is the NTH rule!
        float remainder = fmod(start, important_steps);
        LOGMTRTTIINFO("        "<<" legend at px"<<y<<" with marker "<<start<<" Marker remainder:"<<remainder<<'\n');
        if(remainder==0) {
            // Draw highlighted rule
        }
        else {
            // Draw normal rule
        }
    }

问题是fmod相当不可靠。检查此日志输出，其中可以除以0.1 的值0.1中返回fmod：

Legend from 95.9 to 96.3097 by 0.05, numbers (important_steps): 0.1
         legend at px240 with marker 95.9 Marker remainder:3.60822e-16
         legend at px211 with marker 95.95 Marker remainder:0.05
         legend at px181 with marker 96 Marker remainder:0.1
         legend at px152 with marker 96.05 Marker remainder:0.05
         legend at px123 with marker 96.1 Marker remainder:0.1
         legend at px93 with marker 96.15 Marker remainder:0.05
         legend at px64 with marker 96.2 Marker remainder:0.1
         legend at px35 with marker 96.25 Marker remainder:0.05
         legend at px5 with marker 96.3 Marker remainder:0.1

我想我可以通过添加important_steps==remainder来表达这一点，但如果它实际上返回分母，那么函数是否有缺陷，%（模数）不应该发生？

如何充分肯定地克服这个问题？ Testing snippet available.

顺便说一句，important_steps大于或等于1后，这是多么好用：

Answer 1

也许最好的方法是舍入到整数，然后检查差异，如下所示：

float quotient = start / important_step;
int quot_int = round(quotient);
if (abs(quotient - quot_int) < 1e-10)
{
    // Draw highlighted rule
}
else
{
    // Draw normal rule
}

编辑：圆形功能

int round(double x){return floor(x + 0.5);}