iOS在两种颜色之间的点处查找颜色 [英] iOS Find Color at Point Between Two Colors

问题描述

我遇到了一个问题：我需要能够采用两种颜色并从中制作出虚拟渐变。然后我需要能够在这一行的任何一点找到颜色。我目前的做法是：

I have a problem: I need to be able to take two colors and make a 'virtual gradient' out of them. I then need to be able to find the color at any point on this line. My current approach is this:

if (fahrenheit < kBottomThreshold)
{
    return [UIColor colorWithRed:kBottomR/255.0f green:kBottomG/255.0f blue:kBottomB/255.0f alpha:1];
}
if (fahrenheit > kTopThreshold)
{
    return [UIColor colorWithRed:kTopR/255.0f green:kTopG/255.0f blue:kTopB/255.0f alpha:1];
}

double rDiff = kTopR - kBottomR;
double gDiff = kTopG - kBottomG;
double bDiff = kTopB - kBottomB;

double tempDiff = kTopThreshold - kBottomThreshold;

double rValue;
double gValue;
double bValue;

rValue = kBottomR + ((rDiff/tempDiff) * fahrenheit);
gValue = kBottomG + ((gDiff/tempDiff) * fahrenheit);
bValue = kBottomB + ((bDiff/tempDiff) * fahrenheit);

return [UIColor colorWithRed:rValue/255.0f green:gValue/255.0f blue:bValue/255.0f alpha:1];

变量：

• fahrenheit 是一个传递给我的函数的变量，它是我要为其找到颜色的虚拟行上的数字。


• kTopR ， kTopB ， kTopG 是RGB渐变的一端的值。他们的 kBottom 同行相同。


• kBottomThreshold 和 kTopThreshold 是渐变的终点。

• fahrenheit is a variable passed into my function that is the number on this virtual line that I want to find the color for.
• kTopR, kTopB, and kTopG are the RGB values for one end of the gradient. Same for their kBottom counterparts.
• kBottomThreshold and kTopThreshold are the endpoints of my gradient.

这是我的问题： 当 fahrenheit 越过渐变的任一端时，渐变似乎跳到不同的值。

Here's my problem: When fahrenheit goes over either end of the gradient, the gradient seems to 'jump' to a different value.

我已经在我的S3服务器上托管了一个示例项目，这里。

I've included an example project, hosted on my S3 server, here.

您真的需要下载项目并在模拟器/设备上尝试看看我的意思 （除非你很聪明，只能通过查看代码来判断）

You really need to download the project and try it on the simulator/device to see what I mean (unless you are crazy smart and can tell just by looking at the code)

推荐答案

问题是你没有从 farenheit 中减去 kBottomThreshold 。

The problem is that you're not subtracting kBottomThreshold from farenheit.

但是让我们简化。

F.首先，我们要将输入温度映射到[0 ... 1]范围内的参数 t 。然后，我们要将 t 映射到[ kBottomR ... 范围内的输出kTopR ]，以及[ kBottomG ... kTopG 范围内的输出]，以及[ kBottomB ... kTopB ]范围内的输出。

First, we want to map the input temperature to a parameter t in the range [0 ... 1]. Then, we want to map t to an output in the range [kBottomR ... kTopR], and also to an output in the range [kBottomG ... kTopG], and also to an output in the range [kBottomB ... kTopB].

UIColor *colorForDegreesFahrenheit(double fahrenheit) {
    double t = (fahrenheit - kBottomThreshold) / (kTopThreshold - kBottomThreshold);

    // Clamp t to the range [0 ... 1].
    t = MAX(0.0, MIN(t, 1.0));

    double r = kBottomR + t * (kTopR - kBottomR);
    double g = kBottomG + t * (kTopG - kBottomG);
    double b = kBottomB + t * (kTopB - kBottomB);

    return [UIColor colorWithRed:r/255 green:g/255 blue:b/255 alpha:1];
}

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