如何在Java中繪製RGB色輪

Question

我想繪製Java中的RGB色輪，但無法通過圓形獲得漸變。我只是想在屏幕上繪製它，根本沒有用戶交互。

這是我對現在：

public void paint (Graphics g){ 
     super.paint(g); 

     int red = 255; 
     int green = 0; 
     int blue = 0; 
     int x1 = 500; 
     int y1 = 305; 
     int x2 = 500; 
     int y2 = 50; 

     while (green != 255){ 
      g.setColor(new Color(red, green, blue)); 
      green++; 
      g.drawLine(x1, y1, x2, y2); 
      x2++; 
      if (y2 < y1){ 
       y2++; 
      } 
     } 
     while (red != 0){ 
      g.setColor(new Color(red, green, blue)); 
      red--; 
      g.drawLine(x1, y1, x2, y2); 
      x2--; 
      y2++; 
     } 
     x2 = 500; 
     while (blue != 255){ 
      g.setColor(new Color(red, green, blue)); 
      blue++; 
      g.drawLine(x1, y1, x2, y2); 
      x2--; 
      if (y2 > y1){ 
       y2--; 
      } 
     } 

     while (red != 255){ 
      green--; 
      g.setColor(new Color(red, green, blue)); 
      red++; 
      g.drawLine(x1, y1, x2, y2); 
      x2++; 
      y2--; 
     } 
    }     
} 

Which draws the gradient like this

這是what I want

Answer 1

這是我在Java畫一個RGB色輪的解決方案：

public class Main { 

    public static void main(String[] args) { 
     int rad = 1024; 
     BufferedImage img = new BufferedImage(rad, rad, BufferedImage.TYPE_INT_RGB); 

     // Center Point (MIDDLE, MIDDLE) 
     int centerX = img.getWidth()/2; 
     int centerY = img.getHeight()/2; 
     int radius = (img.getWidth()/2) * (img.getWidth()/2); 

     // Red Source is (RIGHT, MIDDLE) 
     int redX = img.getWidth(); 
     int redY = img.getHeight()/2; 
     int redRad = img.getWidth() * img.getWidth(); 

     // Green Source is (LEFT, MIDDLE) 
     int greenX = 0; 
     int greenY = img.getHeight()/2; 
     int greenRad = img.getWidth() * img.getWidth(); 

     // Blue Source is (MIDDLE, BOTTOM) 
     int blueX = img.getWidth()/2; 
     int blueY = img.getHeight(); 
     int blueRad = img.getWidth() * img.getWidth(); 

     for (int i = 0; i < img.getWidth(); i++) { 
      for (int j = 0; j < img.getHeight(); j++) { 
       int a = i - centerX; 
       int b = j - centerY; 

       int distance = a * a + b * b; 
       if (distance < radius) { 
        int rdx = i - redX; 
        int rdy = j - redY; 
        int redDist = (rdx * rdx + rdy * rdy); 
        int redVal = (int) (255 - ((redDist/(float) redRad) * 256)); 

        int gdx = i - greenX; 
        int gdy = j - greenY; 
        int greenDist = (gdx * gdx + gdy * gdy); 
        int greenVal = (int) (255 - ((greenDist/(float) greenRad) * 256)); 

        int bdx = i - blueX; 
        int bdy = j - blueY; 
        int blueDist = (bdx * bdx + bdy * bdy); 
        int blueVal = (int) (255 - ((blueDist/(float) blueRad) * 256)); 

        Color c = new Color(redVal, greenVal, blueVal); 

        float hsbVals[] = Color.RGBtoHSB(c.getRed(), c.getGreen(), c.getBlue(), null); 

        Color highlight = Color.getHSBColor(hsbVals[0], hsbVals[1], 1); 

        img.setRGB(i, j, RGBtoHEX(highlight)); 
       } else { 
        img.setRGB(i, j, 0xFFFFFF); 
       } 
      } 
     } 

     try { 
      ImageIO.write(img, "png", new File("wheel.png")); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
    } 

    public static int RGBtoHEX(Color color) { 
     String hex = Integer.toHexString(color.getRGB() & 0xffffff); 
     if (hex.length() < 6) { 
      if (hex.length() == 5) 
       hex = "0" + hex; 
      if (hex.length() == 4) 
       hex = "00" + hex; 
      if (hex.length() == 3) 
       hex = "000" + hex; 
     } 
     hex = "#" + hex; 
     return Integer.decode(hex); 
    } 
} 

Answer 2

改變亮度

From here，這似乎是最簡單的方法來提亮顏色是通過將其轉換爲HSB。

float hsbVals[] = Color.RGBtoHSB(originalColor.getRed(), 
            originalColor.getGreen(), 
            originalColor.getBlue(), null); 

    Color highlight = Color.getHSBColor(hsbVals[0], hsbVals[1], 
     0.5f * (1f + hsbVals[2])); // Play with this part to modify rate of change 

使其成爲圓形

從你所擁有的，它看起來像你基本上需要清除所有，但一個圓形區域在中間。

從this answer看來，Area類似乎是最簡單的。

public void paintComponent(Graphics g) { 
     Graphics2D g2 = (Graphics2D)g.create(); 
     Rectangle2D rectangleNotToDrawIn = new Rectangle2D.Double(100, 100, 20, 30); 
      // You will need to find out what size ellipse you need 
     Area outside = calculateOutside(rectangleNotToDrawIn); 

     // draw color wheel here 

     g2.setPaint(Color.black); // assuming you want black 
     g2.setClip(outside); 
     g2.drawLine(0, 0, getWidth(), getHeight()); 

    } 

// Change this method to take in an ellipse shape. 
    private Area calculateOutside(Rectangle2D r) { 
     Area outside = new Area(new Rectangle2D.Double(0, 0, getWidth(), getHeight())); 
     outside.subtract(new Area(r)); 
     return outside; 
    }