簡單的代碼 - 錯誤讓我瘋了......浮到2個字節，回

Question

不知道我是如何完成的學校不能夠解決這個小問題...

下面的代碼會產生意想不到的輸出：

public Color getPixel(int x, int y){ 
    return img.getPixelReader().getColor(x, y); 
} 
public float colorToHeight(Color c){ 
    int b =(int)(c.getBlue()*256); 
    int r =(int)(c.getRed()*256*256); 
    float h = (b+r)/2; 
    h-=10000; 
    return h; 
} 
public Color heightToColor(float h){ 
    h+=10000; 
    h*=2;   
    double r= (int)(h/(256)); 
    double b = h-(r*256); 
    return new Color(r/256,0,b/256,1f); 
} 
public void debugPixel(int x, int z){ 

    System.out.println("test 424->Color: "+heightToColor(424f)); 
    System.out.println("test Color->424: "+colorToHeight(heightToColor(424f))); 
    System.out.println("test Color->424->Color: "+heightToColor(colorToHeight(heightToColor(424f)))); 
    System.out.println("check A: "+getPixel(x,z) + " Height: "+colorToHeight(getPixel(x,z))); 
    System.out.println("check B: "+heightToColor(colorToHeight(getPixel(x,z)))); 
    System.out.println("check C: "+getPixel(x,z)); 
} 

輸出：

test 424->Color: 0x510070ff 
test Color->424: 424.0 
test Color->424->Color: 0x510070ff 
check A: 0x5200cbff Height: 638.0 
check B: 0x53001cff 
check C: 0x5200cbff 

我絕對不找原因【檢查B]的原因= [查看A] ....謝謝！

Answer 1

首先，固定師：

float h = (b + r)/2f; 

原代碼首先執行整數除法，然後將其轉換爲浮動，例如(1 + 2)/2 == 1.0。修復後，它評估爲(1 + 2)/2.0 == 1.5。

因此，在第二個測試案例的高度應爲：

red = 83 
blue = 29 
height = 638.5 

雖然與不正確的整數除法：

height = 638.0 // 0.5 truncated off 
red = 83 
blue = 28 // while 29 is expected 

關於RGB邊界，如果Color類的範圍內操作0..255，定影時，由於需要2不同常量—一個RGB上LIMIT，並且該組合物照顧：

private static final int LIMIT = 255; 
private static final int SHIFT = 256; // or whatever > LIMIT, e.g. 1000 

public float colorToHeight(Color c){ 
    int b = (int) Math.round(c.getBlue() * LIMIT); 
    int r = (int) Math.round(c.getRed() * LIMIT); 
    float h = (b + r * SHIFT)/2f; 
    h -= 10000; 
    return h; 
} 

public Color heightToColor(float h){ 
    h += 10000; 
    h *= 2;   
    double r = (int) (h/SHIFT); 
    double b = h - (r * SHIFT); 
    return new Color(r/LIMIT, 0, b/LIMIT, 1f); 
} 

Answer 2

由於後面的操作（colorToHeight或heightToColor）涉及浮點操作，因此無法確定您獲得的值是否相同，因此會發生精度損失。

你可以重寫你的方法，而無需使用浮點，不是因爲所有的部門，甚至可以用轉移來完成。

public int colorToHeight(Color c){ 
    int b = c.getBlue()>>8; 
    int r = c.getRed()>>16; 
    int h = (b+r)/2; // will be an integer, b and r are even 
    h-=10000; 
    return h; 
} 
public Color heightToColor(int h){ 
    h+=10000; 
    h*=2;   
    int r= h>>8; 
    int b = h-(r<<8); 
    return new Color(r>>8,0,b>>8,1f); 
}