# Dazzling Light¶

In the previous project, we learned to use some simple functions to make RGB Matrix HAT work. So here, we will use the `draw_line()` function with different colors to make RGB Matrix HAT make more cool effects. Run the code

As the program runs, you will see the colors on the RGB Matrix HAT changing from right to left.

```cd /home/pi/rgb_matrix/raspberrypi
sudo python3 dazzling_lights.py
```

Code

Note

You can Modify/Reset/Copy/Run/Stop the code below. But before that, you need to go to source code path like `rgb_matrix/raspberrypi`. After modifying the code, you can run it directly to see the effect.

```from rgb_matrix import RGB_Matrix
import time

def ColorHSV(hue):

if hue < 510:  # Red to Green-1
b = 0
if hue < 255:  #   Red to Yellow-1
r = 255
g = hue  #     g = 0 to 254
else:  #   Yellow to Green-1
r = 510 - hue  #     r = 255 to 1
g = 255

elif hue < 1020:  # Green to Blue-1
r = 0
if hue < 765:  #   Green to Cyan-1
g = 255
b = hue - 510  #     b = 0 to 254
else:  #   Cyan to Blue-1
g = 1020 - hue  #     g = 255 to 1
b = 255

elif hue < 1530:  # Blue to Red-1
g = 0
if hue < 1275:  #   Blue to Magenta-1
r = hue - 1020  #     r = 0 to 254
b = 255
else:  #   Magenta to Red-1
r = 255
b = 1530 - hue  #     b = 255 to 1

else:  # Last 0.5 Red (quicker than % operator)
r = 255
g = b = 0

list = [r, g, b]
return list

def flash():
list = [[0, 0, 0, 7],
[1, 0, 1, 7],
[2, 0, 2, 7],
[3, 0, 3, 7],
[4, 0, 4, 7],
[5, 0, 5, 7],
[6, 0, 6, 7],
[7, 0, 7, 7]]

firsthue = 0
hue = 0
while firsthue < 1530:
j = 0
for i in list:
hue = firsthue + j * 95
j = j + 1
if hue > 1530:
hue = hue - 1530
temp = ColorHSV(hue)
#print(temp,temp,temp)
#time.sleep(2)
rr.draw_line(i, (temp, temp, temp))
rr.display()
firsthue = firsthue + 11

if __name__ == "__main__":
rr = RGB_Matrix(0X74)

while True:
flash()
```

How it works?

In reality, there are three primary colors of red, yellow, and blue, and there are generally three primary colors of red, green, and blue in the display screen, that is, RGB. Their values ​​are generally used FF0000,00FF00,0000FF means, converted to decimal is (255,0,0),(0,255,0),(0,0,255). This website can help us better understand the three primary colors.

```def ColorHSV(hue):

if hue < 510:  # Red to Green-1
b = 0
if hue < 255:  #   Red to Yellow-1
r = 255
g = hue  #     g = 0 to 254
else:  #   Yellow to Green-1
r = 510 - hue  #     r = 255 to 1
g = 255

elif hue < 1020:  # Green to Blue-1
r = 0
if hue < 765:  #   Green to Cyan-1
g = 255
b = hue - 510  #     b = 0 to 254
else:  #   Cyan to Blue-1
g = 1020 - hue  #     g = 255 to 1
b = 255

elif hue < 1530:  # Blue to Red-1
g = 0
if hue < 1275:  #   Blue to Magenta-1
r = hue - 1020  #     r = 0 to 254
b = 255
else:  #   Magenta to Red-1
r = 255
b = 1530 - hue  #     b = 255 to 1

else:  # Last 0.5 Red (quicker than % operator)
r = 255
g = b = 0

list = [r, g, b]
return list
```

Because red is centered on the rollover point (the +32768 above, essentially a fixed-point +0.5), the above actually yields 0 to 1530, where 0 and 1530 would yield the same thing. Rather than apply a costly modulo operator, 1530 is handled as a special case below.

So you’d think that the color “hexcone” (the thing that ramps from pure red, to pure yellow, to pure green and so forth back to red, yielding six slices), and with each color component having 256 possible values (0-255), might have 1536 possible items (6*256), but in reality there’s 1530. This is because the last element in each 256-element slice is equal to the first element of the next slice, and keeping those in there this would create small discontinuities in the color wheel. So the last element of each slice is dropped…we regard only elements 0-254, with item 255 being picked up as element 0 of the next slice. Like this:

• Red to not-quite-pure-yellow is: 255, 0, 0 to 255, 254, 0

• Pure yellow to not-quite-pure-green is: 255, 255, 0 to 1, 255, 0

• Pure green to not-quite-pure-cyan is: 0, 255, 0 to 0, 255, 254

• and so forth.

Hence, 1530 distinct hues (0 to 1529), and hence why the constants below are not the multiples of 256 you might expect.

```def flash():
list = [[0,0,0,7],
[1,0,1,7],
[2,0,2,7],
[3,0,3,7],
[4,0,4,7],
[5,0,5,7],
[6,0,6,7],
[7,0,7,7]]
```

The list `list` stores the starting and ending coordinates of the 8 vertical lines (from left to right), so that each line can be given a different color in the code later to achieve the colorful effect.

```firsthue = 0
hue = 0
while firsthue < 1530:
j = 0
for i in list:
hue = firsthue + j*95
j = j + 1
if hue > 1530:
hue = hue-1530
temp = ColorHSV(hue)
rr.draw_line(i,(temp,temp,temp))
rr.display()
firsthue = firsthue + 11
```

`firshue` and `hue` are passed to `ColorHSV()` as parameters.

Define a two-layer loop, the inner for loop is to draw eight lines in eight different colors, The outer while loop is to add 11 to the `hue` values ​​of the eight colors to achieve the effect of color flow.

For example, in the first for loop, 0, 95, 190, 285, 380, 475, 570, 665 are used as the `hue` value of the initial color of the 8 lines, and then enter the outer loop to increase the `hue` value of each line color by 11 to become 11, 106, 201, 296, 391, 486, 581, 676 to achieve the effect of line color sliding.