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ShootRefreshView is a refresh animation. In fact, It's an animation that opens the shutter. the main point of this animation is how to draw the five line of the shutter. Mainly related to the formula of the circle and line.

Note: the following uses the 'Shutter line' represent the six lines of the shutter.

Step 1: Rotate the 'Shutter line', but the shutter does not open.
The red arc indicates the rotation of the 'Shutter line'

Step 2: Rotate the 'Shutter Line' and open the shutter.
The core idea is how to calculate the intersection of two lines on the following picture.

The following is the formula

Step3: Take the center of the 'Shutter Line' as the base point, and zoom 'Shutter Line'
The core idea is how to calculate the intersection of a lines and a circle on the following picture.

The following is the formula

Step4: Perform a refresh animation, rotate the gradient ring
The last step is easy to implement, just set the SweepGradient to the Paint and draw a circle.

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